Perovskite Heterostructures for Optoelectronic Applications

ABSTRACT

Perovskite heterostructures, which integrate two or more functional materials into one coupled system, have emerged as an important strategy for stabilizing perovskite materials and enabling high‐performance optoelectronic devices. Through rational design of composition and interfaces, these heterostructures can reduce defect density, suppress ion migration, relieve structural strain, and improve resistance to moisture, heat, and light. They can also combine the complementary advantages of different components in structural and optoelectronic properties. These features give perovskite heterostructures clear benefits for both material stability and device operation. In solar cells, they enhance interfacial stability and device durability, while supporting efficient charge extraction. In light‐emitting diodes, they help maintain phase and emission stability, suppress non‐radiative losses, and extend operational lifetime. In this Review, we summarize recent advances in the design, compositional engineering, interfacial mechanisms, and optoelectronic applications of perovskite heterostructures. We also discuss the key challenges and future directions in this field.

Perovskite heterostructures play a central role in enabling next‐generation high‐performance optoelectronic devices, yet balancing efficiency and long‐term stability remains challenging. This Review summarizes composition and dimensionality strategies to optimize band alignment, lattice strain, interfacial defects, carrier dynamics, and ion migration, thereby boosting efficiency and long‐term stability against light, heat, and moisture.

1. Introduction

Metal halide perovskites have emerged as one of the most promising semiconductor families for optoelectronic applications [1, 2, 3, 4]. Their success arises from a unique combination of properties, including strong optical absorption, tunable bandgaps, high charge‐carrier mobility, long carrier diffusion lengths, and remarkable defect tolerance [5, 6, 7]. Over the past decade, these advantages have driven rapid progress in perovskite solar cells (PSCs), perovskite light‐emitting diodes (PeLEDs), photodetectors (PDs), and other optoelectronic devices [8, 9, 10, 11, 12]. In several cases, the device performance has approached that of established inorganic semiconductors [13].

Despite this progress, stability remains a central challenge for perovskite materials and devices [14]. The soft ionic lattice of perovskites makes them vulnerable to moisture, heat, light, and electric fields [15]. Under these conditions, they can undergo ion migration, lattice distortion, phase segregation, and interfacial degradation. These processes reduce efficiency and limit device lifetime. In addition, defects, grain boundaries, and poorly matched interfaces often introduce severe non‐radiative recombination and further undermine operational stability [16]. Therefore, improving stability without sacrificing optoelectronic performance has become a key objective in perovskite research.

Perovskite heterostructures provide an effective route to address this challenge. In general, perovskite heterostructures are formed by integrating two or more materials with different compositions, dimensionalities, phases, or functions into one coupled system [17, 18]. Owing to the structural and compositional versatility of perovskites, heterostructure engineering offers a powerful platform to tailor interfacial chemistry, lattice coupling, and energy landscapes [19, 20]. Properly designed heterostructures can passivate defects, suppress ion migration, relieve strain, and protect perovskites from environmental degradation [21, 22]. At the same time, they can maintain or enhance device performance by optimizing charge extraction, carrier confinement, and recombination pathways [23]. This combination of structural stabilization and efficient operation highlights heterostructure engineering as a key strategy for advancing perovskite optoelectronics [24].

Recent years have witnessed rapid development of perovskite heterostructures across a wide range of material systems and device architectures [25]. These include heterostructures based on compositional engineering, dimensional engineering, and hybrid‐systems that couple perovskites with organic, inorganic, or low‐dimensional materials [26]. For solar cells, perovskite heterostructures can enhance interfacial robustness, improve device durability, and facilitate efficient carrier extraction. For light‐emitting diodes, perovskite heterostructures can stabilize emissive phases, suppress non‐radiative losses, and extend operational lifetime [27, 28]. For photodetectors, they can improve environmental tolerance and operational reliability while enabling broader functionality. These advances highlight the key role of perovskite heterostructures in enabling efficient and stable perovskite optoelectronics [29].

In this Review, we first introduce the definition, classification, and interfacial regulation mechanisms of perovskite heterostructures. We then summarize recent progress in their design strategies from the perspectives of compositional engineering and dimensional engineering and hybrid‐systems. Next, we discuss how heterostructures regulate stability and optoelectronic properties, with an emphasis on their roles in solar cells, light‐emitting diodes, and photodetectors. Finally, we outline the key challenges and future directions in this field.

2. Definition and Classification of Perovskite Heterostructures

Perovskite heterostructures refer to coupled system formed by integrating two or more semiconductor materials with distinct band structures, chemical compositions, or structural dimensionalities through lattice coherent or van der Waals interactions.

To address the intrinsic instability of perovskites, constructing heterostructures has become an important approach to enhance stability [24, 30, 31]. Based on their architecture, heterostructure strategies for perovskite stabilization can be mainly divided into three categories: compositional heterostructures, dimensional heterostructures, and hybrid heterostructures [30]. Compositional heterostructures focus on modulating A‐site cations and X‐site halide ions to further construct spatially tailored or compositionally graded interfaces, thereby achieving simultaneous defect passivation and strain regulation in both the bulk and the surface (Figure 1a) [30, 32]. Dimensional heterostructures focus on the composite construction of mixed‐dimensional perovskites, such as 2D/3D perovskite heterostructures, 2D/2D perovskite heterostructures, and 0D/2D perovskite heterostructures (Figure 1b). Hybrid heterostructures involve the combination of perovskites with functional materials such as 2D materials, colloidal quantum dots (CQDs), and metal‐organic frameworks (MOFs) (Figure 1c). By rationally designing heterostructures via the above strategies and integrating them into devices such as PSCs, LEDs, and PDs, synergistic improvements can be achieved. These improvements include enhanced device stability and better optoelectronic performance. Furthermore, from the perspective of spatial distribution, perovskite heterostructures can be classified into three types (Figure 2): i) Vertical heterostructures, which form compositional or dimensional gradients along the film thickness direction, establishing built‐in electric fields to promote directional charge collection. ii) Lateral heterostructures, which create heterointerfaces within the film plane through selective growth or diffusion, suitable for micro/nano optoelectronic integration. iii) Bulk heterostructures, where heterointerfaces are uniformly distributed throughout the entire film, maximizing defect passivation and suppressing long‐range ion migration. The construction strategies for the three types of heterostructures that can stabilize perovskite materials are detailed below [3].

FIGURE 1.

Three types of heterostructure strategies for perovskite stabilization classified by architecture. (a) Schematic illustration of compositional heterostructure engineering. (b) Schematic illustration of dimensional heterostructures. (c) Schematic illustration of hybrid heterostructures. In this figure, “PVSK” refers to perovskite, “CQDs” refers to colloid quantum dots, and “TMD” refers to transition metal dichalcogenides.

FIGURE 2.

Heterostructures with vertical (a), lateral (b), and bulk (c) spatial phase distributions.

The construction of compositional heterostructures mainly involves A‐site cation modulation and X‐site halide anion modulation within the 3D bulk perovskite system, creating heterostructures at the perovskite bulk or interfaces. On the one hand, regarding A‐site cations, by introducing two or more organic/inorganic cations, such as cesium (Cs⁺), rubidium (Rb⁺), methylammonium (CH₃NH₃ ⁺, MA⁺), formamidinium (CH (NH₂)₂ ⁺, FA⁺), etc., and utilizing their ionic radius differences, heterostructures can be constructed to effectively tune octahedral tilting and improve crystal quality [33, 34]. On the other hand, regarding X‐site halide anions, due to the large differences in ionic radii among halide ions (chloride (Cl⁻), bromide (Br⁻), iodide (I⁻)), the corresponding perovskite lattice constants differ significantly. When heterostructures are constructed using different halide perovskites, substantial lattice strain forms at the interface, thereby affecting perovskite performance.

Dimensional engineering mainly includes three types: 2D/3D heterostructures, 2D/2D heterostructures, and 0D/2D heterostructures. Among these, 2D/3D heterostructures, which integrate 2D perovskites with 3D bulk perovskites, are the most widely studied type. By changing the organic ligand molecules, the properties of 2D/3D heterostructures can be effectively tuned. 2D/2D heterostructures assemble different types of 2D perovskites in‐plane or out‐of‐plane, enabling the construction of vertical heterostructures, lateral heterostructures, or mosaic heterostructures. Furthermore, 0D/2D heterostructures assemble 0D perovskite nanocrystals with 2D perovskites, utilizing the physical protection of the 2D component to isolate moisture and oxygen erosion, suppressing phase transition and surface degradation of the 0D material.

Hybrid‐system heterostructures combine perovskites with non‐perovskite functional materials. They utilize mechanisms such as physical blocking, lattice anchoring, and spatial confinement to construct high‐quality heterointerfaces. This effectively suppresses perovskite degradation, phase transition, and ion migration, significantly enhancing their environmental stability and operational lifetime. Depending on the functional material, there are three main types of heterostructures: conventional 2D material/perovskite heterostructures, CQD/perovskite heterostructures, and MOF/perovskite heterostructures. Among them, typical 2D materials like transition metal dichalcogenides (TMD), such as tungsten diselenide (WSe₂), feature atomic‐level thickness, dangling‐bond‐free surfaces and superior compactness. They can form ultra‐thin physical barriers on perovskite surfaces, and build atomically sharp interfaces via van der Waals interaction or solution self‐assembly. Colloidal quantum dots, with their rigid inorganic lattices, form coherent or semi‐coherent interfaces with perovskites, kinetically suppressing phase transition and ion migration through lattice anchoring effects. MOFs, through the spatial confinement of their 3D frameworks, isolate perovskite nanocrystals from each other, blocking agglomeration and long‐range ion diffusion.

Epitaxial heterostructure represents a key route for constructing high‐quality perovskite heterointerfaces, enabling atomically ordered growth on substrates or templates through lattice matching or well‐defined interfacial orientation relationships. It is characterized by periodic atomic arrangement and controllable heterointerface. Its role will be further systematically discussed in the context of compositional, dimensional, and hybrid‐system heterostructures.

As discussed above, by integrating materials with distinct lattice structures and functional properties, perovskite heterostructures can overcome the limitations of single‐component systems and offer expanded opportunities for performance enhancement and functional diversifications in perovskite optoelectronic devices. In the following, we systematically review recent progress in structural design, interfacial mechanisms, and optoelectronic device applications of perovskite heterostructures, and highlight the key challenges and future perspectives.

3. Strategies for Modulating Perovskite Heterostructures

3.1. Compositional Heterostructure Engineering

Metal halide perovskites are typical ionic compounds. Both A‐site and X‐site ions can be extensively substituted or mixed with other ions, endowing exceptional tunability to modulate lattice parameters and band structures via compositional engineering [24, 28, 35]. To quantitatively characterize the structural stability of perovskites, the tolerance factor (t) is commonly adopted for evaluation. Its formula is

$$t=\frac{\left(R_A+R_B\right)}{\sqrt{2}\left(R_A+R_X\right)}$$ (1)

where R _A, R _B and R _X represent the ionic radii of A‐site, B‐site and X‐site ions respectively. Studies and practical experience prove that perovskite crystals maintain stable structures when t ranges from 0.78 to 1.05 [34, 36]. Currently, a prevalent strategy to enhance crystal structural stability is constructing alloyed perovskites by introducing A‐site and X‐site ions with varied sizes, so as to bring the tolerance factor into a favorable range [37, 38]. Nevertheless, compositional segregation tends to occur frequently in practical applications [39, 40, 41]. We notice that recent studies have constructed compositional heterostructures based on lattice constant differences between diverse perovskite systems. Local strain is thereby introduced into target perovskites to raise the phase transition barrier, which effectively improves phase stability. Herein, we elaborate the strategies for fabricating compositional heterostructures and their stabilization mechanisms from cation and halogen regulation perspectives.

3.1.1. Cation Engineering

Modulation of A‐site cation composition can effectively boost perovskite stability without introducing extra interfacial layers. Nevertheless, mixed cation approaches fail to fully relieve residual stress in films. Given that substrates such (glass/ Indium Tin Oxide (ITO)) possess a much lower thermal expansion coefficient, tensile stress accumulates in the in‐plane direction of perovskites during annealing and cooling. Zhao et al. found that tensile stress elongates lead (Pb)‐I bonds and reduces the activation energy for ion migration, accelerating the decomposition of perovskite into PbI₂ under illumination [42]. This accelerates the photodegradation of perovskites. To offset residual tensile stress, researchers introduce compressive stress deliberately via interfacial lattice mismatch.

Researchers introduce lattice‐matched buffer layers at the buried interfaces of polycrystalline films to release interfacial strain in device‐oriented configurations. In mesoporous metal halide perovskite solar cells, coexisting tetragonal and cubic phases trigger structural strain at the mesoporous TiO₂ (mp‐TiO₂)/perovskite heterointerface, inducing structural defects and degrading material stability. To address this issue, Ye et al. inserted a lattice‐compatible cubic CsPbBr₃ buffer layer between mesoporous TiO₂ and MAPbI₃ [43]. Due to the lattice matching between α‐CsPbBr₃ and β‐MAPbI₃, the CsPbBr₃ buffer layer can serve as an epitaxial template to induce the relaxed growth of MAPbI₃ in a pure tetragonal phase, thereby releasing the tensile strain at the interface. High‐resolution transmission electron microscopy (HRTEM) analysis shows that only a single, highly ordered tetragonal phase is observed in the CsPbBr₃‑modified sample, indicating effective release of the interfacial strain. This method significantly alleviates the lattice mismatch strain at the interface while yielding high‐purity tetragonal‑phase (β‑phase) MAPbI₃, greatly improving device efficiency and stability. This work demonstrates that inserting a lattice‑matched buffer layer at the buried interface of polycrystalline thin films is an effective route to release residual tensile stress. The method does not require special substrates, is compatible with conventional solution‑based fabrication processes, and is suitable for planar polycrystalline thin‑film devices that need moderate stress relief. The work by Ye et al. shows that constructing heterostructures to introduce stress is an effective strategy for stabilizing perovskites.

To better harness strain for constructing stable heterostructure structures, it becomes essential to achieve controllable stress introduction. Liu et al. reported a representative work in this regard [44]. They introduced a composition‐tunable buried buffer 3D perovskite layer of CsPbCl₃ between a silicon substrate with a pyramid‐textured surface and an overlying photoactive 3D perovskite (Cs_xFA_1‐xPb(I_yBr_1‐y)₃), achieving precise control over the magnitude of compressive stress at the buried interface (Figure 3a). First, by screening all‐inorganic perovskites (CsPbI₃, CsPbBr₃, CsPbCl₃) with different lattice constants as the buried buffer layer, they found that CsPbCl₃, having the smallest lattice constant, can apply a large compressive stress, effectively counteracting the inherent residual tensile stress in the film and achieving overall stress balance inside the perovskite film (Figure 3b). Grazing incidence X‐ray diffraction (GIXRD) confirmed that the introduction of CsPbCl₃ brings the stress nearly to zero. They further tuned the thickness of the CsPbCl₃ layer to quantify the magnitude of the stress and found that both single‐junction and tandem devices performed best at a thickness of 20 nm. This thickness dependence indicates that the stress magnitude is adjustable, opening new avenues for achieving tunable stress in future work. Ultimately, fully textured perovskite/silicon tandem solar cells based on this strategy achieved a certified steady‐state efficiency of 31.5% and retained over 95% of their initial efficiency after 800 h of continuous operation. However, the limitation of this method is the high cost of vacuum deposition equipment and the need for precise control of the buffer layer thickness. Therefore, further exploration is still needed on how to better exploit compositional heterostructures to enhance the stability of the desired perovskite phase.

FIGURE 3.

Stress regulation and stability enhancement via 3D/3D heterostructures constructed by cation engineering. (a) Schematic illustration of a buried 3D/3D strained heterostructure [44]. Reproduced with permission [44]. Copyright 2024, Elsevier Inc. (b) Schematic diagram showing the application of compressive strain to the upper 3D perovskite film by adjusting the lattice parameter of the buried buffer 3D perovskite layer [44]. Reproduced with permission [44]. Copyright 2024, Elsevier Inc.

3.1.2. Halide Regulation

Due to the significant differences in ionic radii among different halogens, the lattice parameters of perovskites are directly altered. Therefore, by adjusting the halogen ratio, the lattice stress within compositional heterostructures can be precisely tuned. At room temperature, perovskite materials readily undergo a transition from the photoactive phase to the inactive phase. Studies have shown that this phase transition is closely related to the intrinsic tensile stress present in the lattice. This tensile stress lowers the activation energy for the transition from the active phase to the inactive phase, causing the material to degrade within hours to days [36]. To suppress the phase transition, researchers attempt to introduce compressive stress into perovskites by exploiting differences in lattice constants, thereby counteracting tensile stress. On one hand, compressive stress can effectively offset the tensile stress induced by the phase transition, relieving lattice stress in the photoactive phase of the perovskite and suppressing its degradation. On the other hand, compressive stress also increases the difficulty of ion migration within the lattice, thereby delaying the formation and diffusion of defects [45]. Based on the above considerations, Chen et al. stabilized the active phase of FAPbI₃ by constructing halogen‐composition heterostructures. Specifically, they selected a series of mixed‐halide single crystals of MAPbCl_xBr_3‐x with lattice constants smaller than those of α‐FAPbI₃ as the growth substrate [36]. When α‐FAPbI₃ thin films were epitaxially grown on these substrates, the in‐plane lattice dimensions of the substrates were smaller than the natural lattice dimensions of the films. The films were forced to contract to better match the substrates, thereby generating an in‐plane compressive strain of up to 2.4% within the films. The direction of this strain opposes the intrinsic tensile stress in the α phase, and the two cancel each other out. Experimental evidence shows that the strained films retain a pure black α phase after 360 days of storage in air, whereas the same film, once peeled off from the substrate, completely transforms into the yellow δ phase within 24 h. This work validates the feasibility of introducing compressive strain through lattice mismatch and provides a unique stabilization pathway for perovskite systems that are prone to phase transitions, such as α‐FAPbI₃ and CsPbI₃.

In summary, the core of compositional heterostructure engineering lies in exploiting the size and electronegativity differences of A‐site cations and X‐site halide ions to construct compositional heterointerfaces at perovskite film interfaces, introducing compressive stress to suppress phase transitions and ion migration, thereby achieving perovskite stabilization [34, 38, 46].

Although preliminary success has been achieved with this strategy, under real operating conditions, how to effectively suppress ion diffusion and maintain a sharp heterointerface to stably apply lattice stress remains a key challenge limiting its practical application [44, 45]. Therefore, the next step should focus on developing more precise stress regulation techniques and scalable interface engineering strategies, which will fully unlock the application potential of compositional heterostructure engineering and facilitate the development of efficient and stable perovskite optoelectronic devices.

3.2. Dimensionality Engineering

Compared to 3D perovskites, low‐dimensional perovskites exhibit stronger phase stability and greater resistance to external stresses such as environmental, thermal, and light stresses [24, 47]. By introducing organic cations of different sizes, the 3D bulk inorganic framework can be precisely tailored into low‐dimensional organic‐inorganic perovskite structures, including 2D (or quasi‐2D) layered structures, 1D nanowires/nanoribbons, and 0D quantum dots (Figure 4a). Among these, the most common type in quasi‐2D perovskites is the Ruddlesden‐Popper (RP) phase, which uses monoammonium organic cations (e.g., n‐butylammonium, BA⁺) as spacers, with van der Waals gaps between adjacent inorganic layers [48]. The Dion‐Jacobson (DJ) phase, on the other hand, uses diammonium organic cations (e.g., ethylenediammonium, EDA²⁺) to directly bridge adjacent inorganic layers (Figure 4b) [24]. Here, n represents the number of inorganic octahedral layers in an ideal single crystal, whereas in actual polycrystalline films, due to the coexistence of multiple phases and the volatilization of organic cations, the overall average layer number is denoted as ⟨n⟩ (Figure 4c). 1D perovskite nanowires feature grain‐boundary‐free, one‐directional charge transport channels and radial spatial confinement effects [49]. 0D quantum dots, through quantum confinement effects, achieve strong exciton binding energies and tunable bandgaps, exhibiting unique optoelectronic properties [25].

FIGURE 4.

Dimensional regulation of metal halide perovskites. (a) Typical crystal structures of metal halide perovskites, from left to right: 3D, 2D, 1D, and 0D [23]. Reproduced with permission [23]. Copyright 2025, Wiley‐VCH GmbH. (b) Regulation of perovskite phase types (e.g., RP phase, DJ phase) by adjusting different ligands [23]. Reproduced with permission [23]. Copyright 2025, Wiley‐VCH GmbH. (c) Layer thickness control achieved by varying the number of octahedral layers between organic spacers [23]. Reproduced with permission [23]. Copyright 2025, Wiley‐VCH GmbH.

Based on the categories of low‐dimensional perovskites, common dimensional heterostructures mainly include three types: 2D/3D perovskite heterostructures, 2D/2D perovskite heterostructures, and 0D/2D perovskite heterostructures. There are two primary growth methods for dimensional heterostructures. One is to integrate perovskite components of different dimensions via ligand‐ligand interactions. Among these, the van der Waals heterostructure with periodically arranged edge‑on oriented molecules forms a heterointerface with a fully ordered lattice [50]. This yields a robust van der Waals epitaxial heterostructure that effectively enhances material stability [51]. Therefore, mixed‐dimensional perovskite heterostructures can be constructed to maximize the merits of perovskites with different dimensions. This strategy offers a viable way to simultaneously boost device efficiency and long‐term operational stability [26].

3.2.1. 2D/3D Perovskite Heterostructures

2D/3D perovskite heterostructures combine excellent environmental stability with high optoelectronic conversion efficiency, showing broad application prospects in various optoelectronic devices [24]. Depending on the orientation of the 2D layers relative to the 3D substrate, these heterostructures can be classified into two types: horizontal orientation and vertical orientation [52]. In horizontally oriented heterostructures, based on the chemical termination at the interface, they can be further subdivided into monolayer‐ligand‐terminated and bilayer‐ligand‐terminated interfaces (Figure 5a,b) [53]. The former forms atomically sharp interfaces with Type‐II band alignment, favoring charge separation. The latter, due to the increased interlayer spacing from the bilayer ligands that weakens electronic coupling, exhibits Type‐I band alignment dominated by energy transfer [52, 53]. Horizontal structures can densely cover the 3D surface, using hydrophobic organic ligands to provide excellent defect passivation and moisture resistance, but the insulating ligands in the out‐of‐plane direction limit vertical charge transport [54]. In contrast, vertically oriented heterostructures feature 2D perovskite inorganic frameworks perpendicular to the substrate (Figure 5c). Photogenerated carriers can migrate along high‐mobility inorganic [PbX₆]⁴⁻ octahedral frameworks, avoiding insulating ligand layers. This greatly improves out‐of‐plane conductivity. Below, we will introduce several different types of 2D/3D perovskite heterostructures individually.

FIGURE 5.

Schematic illustration of spatial configurations in 2D/3D perovskite heterostructures. There are two fundamental configurations: (a, b) horizontally oriented and (c) vertically oriented structures, where the horizontal configuration can be further classified into A’‐A’‐terminated (a) and A‐A’‐terminated (b) heterostructures.

Directly growing a 2D capping layer on 3D perovskites represents an early and widely adopted approach for constructing horizontally oriented 2D/3D heterostructures [24, 54, 55]. Owing to the presence of hydrophobic organic spacer cations, which effectively block moisture ingress, this configuration significantly improves device stability in humid environments [9]. However, conventional in situ spin‐coating methods often result in mixed n‐value phases, random domain orientation within the 2D layer, and residual unreacted ligands. These factors lead to interfacial energy mismatch and structural disorder, ultimately limiting device performance [24, 56]. To address the issues of poor phase purity and limited interfacial control associated with in situ approaches, alternative strategies have been developed. In particular, direct spin‐coating strategy of pre‐synthesized 2D or quasi‐2D perovskites, enabled by orthogonal solvent engineering, allows for more precise regulation of interfacial structure and composition. Sidhik et al. adopted dielectric constant and Gutmann donor number for selective control [57]. They spin‐coated pre‐synthesized phase‐pure 2D perovskite ink onto the 3D film. A well‐defined and thickness‐controllable 2D capping layer was obtained, and the underlying 3D substrate remained intact. The resulting 2D/3D bilayer solar cells achieved a power conversion efficiency of 24.5% and maintained over 99% of their initial efficiency after 2000 h of continuous 1‐sun illumination at 55°C. This work solved the long‐standing solvent incompatibility issue in solution‐processed 2D/3D heterostructure fabrication, enabling direct coating of phase‐pure, thickness‐controlled 2D capping layers.

As research has progressed, it has been recognized that commonly used ammonium‐based ligands, such as PEA⁺ and BA⁺, are prone to deprotonation under thermal and photo‐induced stress. The resulting amines can further react to form secondary species, leading to the structural collapse of the 2D capping layer structure and severely compromising the photothermal stability of the devices [57, 58]. Through systematic photothermal accelerated aging experiments, Peng et al. further revealed the complete physicochemical mechanism of this degradation process (Figure 6) [59]. In pure 3D devices, PbI₂ decomposes into Pb⁰ and iodine (I₂), generating iodine vacancies and mobilizing existing I⁻, which then reacts with I₂ to form triiodide ion (I₃ ⁻). Ion migration degrades device stability. In mono‐ammonium 2D/3D devices, the co‑decomposition of the mono‐ammonium 2D layer and PbI₂ induces a higher concentration of iodine vacancies and iodine migration, significantly accelerating device degradation. In di‐ammonium 2D/3D devices, the di‐ammonium 2D layer is structurally stable, blocks the movement of iodide ions, and slows the formation of Pb⁰. Iodide ions are confined within the perovskite bulk. Subsequently, iodide ions accumulate at the interface and are bounced back into the lattice interstitials by the 2D layer, forming interstitial iodine (I_i) deep‐level traps, which exacerbate non‑radiative recombination. At the same time, a small amount of Pb° forms and limited iodide ion migration occurs, leading to further slow degradation. The mono‐ammonium 2D layer decomposes under photothermal aging and accelerates ion migration, whereas the di‐ammonium 2D layer, although blocking ions, introduces interstitial defects. Neither perfectly solves the stability problem.

FIGURE 6.

Proposed degradation mechanisms of 2D/3D‐mono, 3D, and 2D/3D‐di perovskite devices under light aging at 85°C. Mono‐ammonium and di‐ammonium are abbreviated as mono‐am and di‐am, respectively [59]. Reproduced with permission [59]. Copyright 2025, RSC.

Therefore, rationally designing organic ligands is essential, such as developing ligands with high pKa values or multiple coordination sites, to construct structurally stable 2D/3D heterointerfaces. Chang et al. introduced an asymmetric meta‐amidinopyridine (MAP) ligand and applied multiple drip‐washing steps with isopropanol after spin‐coating, thereby successfully resolving the issues of random orientation and phase impurity in 2D layers that commonly arise in conventional in situ methods [56]. By utilizing the multiple coordination sites provided by the pyridine nitrogen and amidino groups in the MAP ligand to strongly bind with Pb²⁺ and I⁻, the originally randomly oriented 2D crystalline domains were reconstructed into a highly ordered parallel orientation while maintaining a phase‐pure (n = 1) structure. Grazing‑Incidence Wide‑Angle X‑ray Scattering (GIWAXS) patterns show that although the 2D layer formed by the MAP ligand without drip‐washing is phase‐pure (n = 1), the diffraction rings indicate a disordered domain orientation. After multiple drip‐washing steps, the diffraction pattern exhibits sharp spots along the out‐of‐plane direction, indicating that the 2D domains have transformed into a highly ordered parallel orientation (Figure 7a). High‐resolution electron microscopy images further confirm that the ordered MAP‐2D layer is flat and tightly attached to the 3D perovskite surface, forming a dense heterointerface. This structure shifts the exciton recombination zone from the defect‐rich surface to the interior, while the upper 2D perovskite effectively blocks ion migration and moisture ingress (Figure 7b). Based on this ordered MAP‐2D capping layer, inverted perovskite solar cells achieved a power conversion efficiency of 26.05% (Figure 7c) and retained 82% of their initial efficiency after 1000 h under damp heat testing (85°C/85% relative humidity) and 75% after 840 h under outdoor testing (Figure 7d).

FIGURE 7.

Structural characterization and device performance of 2D/3D heterostructures. (a) GIWAXS comparison of 2D‐MAP under different drip‐washing cycles [56]. Reproduced with permission [56]. Copyright 2025, Springer Nature. (b) HR‐STEM cross‐sectional image comparison of 2D‐MAP before and after drip‐washing [56]. Reproduced with permission [56]. Copyright 2025, Springer Nature. (c) Current density‐voltage (J–V) curves of inverted perovskite solar cells fabricated with 2D/3D‐MAP [56]. Reproduced with permission [56]. Copyright 2025, Springer Nature. (d) Damp‐heat stability test (85°C/85% relative humidity, ISOS‐S‐31) of inverted perovskite solar cells [56]. Reproduced with permission [56]. Copyright 2025, Springer Nature.

Ligand engineering has effectively improved the power conversion efficiency of n‐i‐p structure perovskite solar cells, but this strategy is difficult to apply to inverted (p‐i‐n) device architectures. 2D perovskites have an electron‐blocking effect, which can degrade device performance. Chen et al. successfully fabricated inverted perovskite solar cells with both high efficiency and high stability by tuning the quantum well width of 2D perovskites to weaken the electron‐blocking effect. They used 3‑fluorophenethylamine (3F‑PEA) as spacer ligand and inntroduced a small amount of methylammonium iodide (MAI) in the precursor solution. By controlling the formation kinetics of the 2D phase, a quasi‑2D capping layer dominated by high‑n phases (n ≥ 3) was formed in situ on the 3D perovskite surface, effectively reducing interfacial electron blocking, suppressing ion migration, and passivating defects. Based on this strategy, unencapsulated devices showed no efficiency loss after 1000 h of continuous illumination at room temperature and 50% relative humidity; encapsulated devices retained 92% of their initial efficiency after 500 h of light aging at 65°C under ISOS‑L3 protocols [60].

The 2D/3D heterostructures constructed by the aforementioned strategies are often realized by etching the surface of the 3D perovskite. However, the penetration depth of solvent into the 3D perovskite lattice is difficult to precisely control, often resulting poor uniformity in both composition and dimensional structure. Therefore, developing controllable fabrication strategies for 2D/3D heterostructures with well‐defined composition and structure remains essential. Zhu et al. developed a method of ligand‐welded perovskite epitaxial heterostructures at room temperature, which significantly improves the interfacial order between the 2D and 3D perovskites [61]. They separately synthesized 3D inorganic perovskites and 2D organic‐inorganic hybrid perovskites. The two were mixed at room temperature, and the residual PEA⁺ ions in the 2D perovskite solution replaced the oleic acid (OA)/oleylamine (OLA) ligands on the surface of the 3D perovskite, driving the oriented assembly of CsPbBr₃ nanocubes onto PEA₂PbBr₄ nanosheets. Steady‐state and time‐resolved photoluminescence (PL) spectra revealed efficient charge and energy transfer within the epitaxial heterostructure. This work demonstrated, that perovskite crystals of different dimensions and compositions can self‐assemble at room temperature through ligand‐mediated epitaxial welding, breaking the traditional limitations of high temperature or strict lattice matching required for heteroepitaxy. The strategy is highly versatile and has been extended to various 3D (CsPbBr₃, Cs₂AgBiBr₆, CsPbCl₃, etc.) and 2D (BA₂PbBr₄, NMA₂PbBr₄, etc.) systems. More importantly, this approach decouples heterointerface construction from the independent synthesis of individual component crystals, providing a versatile platform for systematically probing interfacial strain and charge transfer kinetics.

Nevertheless, the current strategy still relies on pre‐synthesized high‐quality nanocrystals, and the assembly efficiency is highly sensitive to the type and concentration of surface ligands. Its extension to large‐area thin films and scalable device integration remains a key challenge for future development. Recently, Lu et al. adopted a solvent‐free vacuum epitaxial growth method to achieve atomic‐level, layer‐by‐layer controlled growth of 3D perovskites on 2D single‐crystal substrates [53]. By co‑heating solid powders of CsBr and PbBr₂ under vacuum, they achieved solvent‑free, layer‑by‑layer heteroepitaxial growth of 3D CsPbBr₃ on a 2D PEA₂PbBr₄ single‑crystal substrate. The researchers found that the 3D CsPbBr₃ grew in a layer‑by‑layer mode on the 2D single‑crystal surface, where the thickness of each layer could be precisely controlled down to a single atomic layer, and the surface roughness of the film was below 0.3 nm. Because this layer‑by‑layer epitaxial growth method produces almost no grain boundaries or dislocations, the heterostructure maintains atomically sharp interfaces over a large area. Such high‑quality crystal structure significantly reduces the energetic disorder inside the material; lower energetic disorder means fewer trap states, so the photoluminescence quantum yield of the heteroepitaxially grown CsPbBr₃ film is more than twice that of samples grown on glass. By adjusting the evaporation conditions, this work also enabled precise construction of two types of interfacial terminations: Cs‑PEA terminated and PEA‑PEA terminated. Theoretical calculations show that the Cs‑PEA terminated interface tends to separate electrons and holes into different material layers, whereas the PEA‑PEA terminated interface facilitates energy transfer from one layer to the other. Researchers can choose the more appropriate interface type according to the actual needs of the device. This solvent‑free, layer‑by‑layer epitaxial growth method eliminates grain boundaries and defects, significantly enhancing the intrinsic structural stability of the perovskite material. Meanwhile, the flexible interfacial band alignment allows good device performance to be achieved without sacrificing charge transport efficiency.

In the aforementioned horizontally oriented 2D/3D perovskite heterostructures, the organic ligand layers are parallel to the substrate. As charge carriers transport along the thickness direction, they must pass through the insulating organic layers, resulting in extremely low out‐of‐plane mobility. Vertically oriented 2D perovskite single crystals can, to some extent, mitigate the out‐of‐plane blocking effect of organic ligands, thereby simultaneously improving the stability and carrier transport performance of the material, which is an ideal configuration long pursued by researchers in this field. Lei et al. employed a single‐crystal epitaxy method to compress the organic spacer layer via a lattice‐mismatched substrate and, for the first time, grew BA₂MA _{n ‐1}Sn _n I_{3 n +1} superlattices on a 3D MAPbBr₃ substrate [62]. In this structure, the inorganic Sn‐I slabs are aligned perpendicular to the substrate and interconnected in‐plane to form a cross‐linked 2D network, achieving efficient carrier transport in three dimensions. Transient photocurrent measurements strongly confirmed that, compared with conventional horizontally oriented 2D/3D perovskite heterostructure single crystals, vertically oriented perovskite heterostructures exhibit higher carrier mobility. This work breaks through the bottleneck of charge transport in low‐dimensional perovskites from a structural design perspective, providing new insights for fabricating efficient and stable perovskite optoelectronic devices. However, single‐crystal epitaxy imposes stringent requirements on the substrate and growth conditions; how to extend this strategy to polycrystalline thin‐film systems remains a key challenge for future research.

Although single‐crystal epitaxy has demonstrated the structural superiority of vertical heterostructures, realizing 2D‐on‐3D vertical heterostructures in thin‐film devices via conventional solution processing remains challenging. This limitation arises because traditional one‐step spin‐coating typically induce random mixing and disordered orientation of 2D and 3D phases. Recently, Ji et al. employed a simple one‐step spin‐coating strategy to successfully construct a vertically graded 2D/3D heterostructure in situ in a quasi‐2D PEA₂(FAPbBr₃) _{n ‐1}PbBr₄ system [63]. They first sequentially spin‐coated poly(9‐vinylcarbazole) (PVK) and polyethylenimine ethoxylated (PEIE) onto an ITO substrate as hole transport layers. The hydroxyl groups in the PEIE molecules form hydrogen bonds with the nitrogen atoms in PVK, while also strongly coordinating with Pb²⁺ ions in the perovskite precursor. This induces bottom‐up, layer‐by‐layer crystallization of the perovskite: a horizontally oriented 3D phase preferentially forms at the bottom, followed by the growth of an organic‐rich 2D phase on top of the 3D layer, with its inorganic framework naturally oriented perpendicular to the substrate. Thus, a vertically graded 2D/3D heterostructure is spontaneously constructed. This vertical orientation allows photogenerated carriers to be directly transported along the high‐mobility inorganic octahedral framework to the 3D layer, avoiding charge blocking by the insulating organic layers in horizontal structures, and significantly enhancing photoluminescence intensity and carrier lifetime. Meanwhile, the 2D capping layer effectively passivates surface defects and suppresses ion migration, greatly improving the environmental and thermal stability of the devices. This strategy requires no pre‐synthesis or epitaxial templates; it forms vertical heterostructures in situ during a single spin‐coating step solely through interface‐anchoring molecules, offering extreme process simplicity and high universality. Future work can further optimize the anchoring molecules, tune the thickness ratio and average n‐value of the 3D and 2D layers, and verify its applicability to other perovskite systems and large‐scale fabrication.

3.2.2. 2D/2D Heterostructures

The 2D halide perovskites, owing to their excellent solution processability and tunable quantum well structures, have become an important class of semiconductor materials for constructing heterostructures [64]. Integrating 2D perovskites with different compositions through spatial assembly to form 2D/2D perovskite heterostructures can enhance the structural stability of perovskites themselves in multiple aspects, such as suppressing ion migration and stabilizing interfacial composition [64, 65]. Due to the anisotropic nature of 2D perovskites, 2D/2D perovskite heterostructures can be further classified into vertical heterostructures (Figure 8a), lateral heterostructures (Figure 8b), and mosaic heterostructures based on their spatial configuration (Figure 8c).

FIGURE 8.

Schematic illustration of spatial configurations of 2D/2D perovskite heterostructures. There are three fundamental configurations: (a) Vertical heterostructure, (b) Lateral heterostructure, and (c) Mosaic heterostructure.

3.2.2.1. Vertical Heterostructure

Vertical 2D/2D perovskite heterostructures are formed by physically stacking two types of 2D perovskite single‐crystal nanosheets with different chemical compositions or different layer thicknesses (n values) along the direction perpendicular to the substrate via van der Waals forces, resulting in atomically sharp layered heterostructures [66].

The organic ligands between the layers can act as diffusion barriers, effectively suppressing the interlayer migration of halide ions through steric hindrance, thereby maintaining the long‐term stability of the heterointerface composition under thermal or electric fields [67]. Pan et al. directly grew large‐area, phase‐pure, and monolayer‐thin Ruddlesden‐Popper perovskite nanosheets at the solution‐air interface, then gently picked up the floating flakes using a PDMS stamp, aligned them under an optical microscope, and sequentially transferred and stacked them onto a target substrate [66]. They stacked BA₂PbBr₄ flakes onto BA₂PbI₄ flakes to form heterostructures. Experiments showed that after storing the heterostructure in a desiccator at room temperature for several weeks, the characteristic peak positions of the two components in the photoluminescence spectra did not shift over time. Their team attributed this stable interface to the organic LA cation layer acting as a diffusion barrier that prevents halide ion migration. This heterostructure allows researchers to flexibly integrate 2D perovskites with different halogens, n‐values, or organic cations. Akriti et al. further revealed the underlying mechanism by which organic cations suppress ion migration [67]. They constructed vertical heterostructures such as BA₂PbBr₄/BA₂MA₂Pb₃I₁₀ via mechanical exfoliation and transfer stacking, and systematically measured the interlayer interdiffusion coefficients of halides for different organic LA cations (BA, PEA, 2P, 2T). They found that when bulky, rigid π‐conjugated cations such as bithiophene ethylammonium were used, the diffusion coefficient was about three orders of magnitude lower than that in the short‐chain aliphatic cation (BA) system. Further analysis revealed that the diffusion behavior of halide ions in vertical heterostructures does not follow the classical continuous diffusion model. Instead, the diffusion process exhibits a layer‐by‐layer “quantized” characteristic. Ions migrate to the subsequent layer only when the bromide‐to‐iodide ratio in the current layer reaches a specific value, corresponding to the most thermodynamically stable mixing composition. This layer‐by‐layer progression mechanism originates from two constraints: first, ions are only allowed to enter the adjacent layer when the halogen composition in the current layer reaches the experimentally observed preferred halogen alloy concentration; second, the organic cations themselves possess an ion‐blocking effect. It is this layer‐by‐layer hopping mechanism that allows vertical heterostructures to maintain sharp interfaces even after heating.

To address the issues of interfacial contamination or damage introduced by mechanical transfer in the transfer‐stacking method, as well as the difficulty of achieving perfect lattice matching, Shi et al. developed a transfer‐free direct solution growth strategy. By exploiting the solubility difference between MA⁺ and 4AMP²⁺ in a 4‐(aminomethyl)piperidinium (4AMP²⁺)‐based DJ phase perovskite, they precisely controlled the temperature profile of the precursor solution to sequentially precipitate the n = 2 and n = 3 phases, forming a vertically stacked quantum well structure [68]. Since both components use pure iodides and the lattice mismatch between the n = 2 and n = 3 phases is less than 0.25%, the 4AMP²⁺ organic layers can release residual strain through weak van der Waals forces. After annealing the heterostructure in air with 50% humidity at 100°C for 48 h, the heterointerface in the photoluminescence image remained sharp and clear, indicating an absence of halide diffusion and ion mixing. This study demonstrates the structural stability of vertical heterostructures under extreme thermal environments.

3.2.2.2. Lateral Heterostructure

Lateral heterostructures refer to heterostructures formed by edge epitaxy of two different 2D perovskite single‐crystal flakes within the same plane, growing coherently along specific crystallographic directions to achieve a continuous lattice, atomically sharp interface, and abrupt compositional change.

Due to the inherent soft ionic lattice and high intrinsic halide ion mobility of 2D perovskites [69, 70], interdiffusion of halide ions at the interface can easily cause interfacial blurring [71]. Therefore, suppressing lateral ion diffusion is a core challenge for achieving stable lateral heterostructures. Shi et al. replaced the conventional flexible alkyl‐chain ligand butylammonium (BA) with the rigid π‐conjugated organic ligand bithiophene ethylammonium (2T) [64]. Using a solution‐phase sequential epitaxy method, they first prepared (2T)₂PbBr₄ flakes and then epitaxially grew (2T)₂PbI₄ at their edges, thereby constructing (2T)₂PbI₄‐(2T)₂PbBr₄ lateral heterostructures. Molecular dynamics simulations and free energy calculations revealed that when the 2T ligand is used, the free energy required to remove a bromide ion from the lattice to create a vacancy is significantly higher than when the BA ligand is used. The higher the vacancy formation energy, the more difficult it is for ions to leave their lattice sites, and thus the ion migration rate is greatly reduced. The rigid π‐conjugated ligand effectively blocks the migration and mixing of halide ions at the lateral heterointerface by increasing the vacancy formation energy and maintaining interfacial structural order, thereby achieving stable lateral heterostructures.

Compared with the well‑established monolayer (n = 1) 2D halide perovskite heterostructures, n > 1 epitaxial heterostructures are more difficult to prepare but can achieve superior optoelectronic properties by weakening quantum confinement effects, making them an important research direction. Xia et al. proposed a kinetic Wulff‑shape heteroepitaxial growth strategy [65]. They first exfoliated flakes from highly phase‑pure bulk single crystals of the 2D perovskite (3T)₂PbI₄ (n = 1–3) as epitaxial seeds. By adjusting the polarity of the mixed solvent, controlling the growth temperature, rate, and time, and employing an intermittent growth interruption method, the epitaxial crystals spontaneously grew into thermodynamically stable rectangular morphologies. Using this approach, they successfully fabricated (3T)₂MA _{n ‐1}Pb _n I_{3 n +1}‐(3T)₂MA _{n ‐1}Sn _n I_{3 n +1} (n = 1–3) lateral heterostructures. The core of this method lies in finely tuning the growth kinetics so that the crystallization path of the system always avoids the metastable regions prone to precipitating impurity phases with different n‑values, thereby suppressing the spontaneous nucleation of unwanted phases. In practice, the perovskite phase with lower solubility is chosen as the inner seed region, while the component with higher solubility serves as the outer epitaxial region. Combined with control of solvent polarity, the risk of re‑dissolving the seed crystals during epitaxy is minimized. Meanwhile, the reaction is actively stopped after a few minutes of growth to avoid homogeneous nucleation of by‑products on the substrate. The work by Xia et al. effectively addresses the issue of impurity phase nucleation in n > 1 systems and achieves lateral heterostructures with controllable layer thickness and high tolerance to lattice mismatch.

3.2.2.3. Mosaic Heterostructure

In addition to vertical and lateral 2D/2D heterostructures, researchers have recently developed a novel type of mosaic heterostructure. This embedded structure eliminates the lattice mismatch and defect states commonly present at conventional heterointerfaces, thereby significantly suppressing non‐radiative recombination and enhancing charge transport efficiency as well as device operational stability [72]. Zhang et al. constructed seamlessly embedded mosaic lateral heterostructures inside 2D perovskite single crystals using a strain‐driven spontaneous etching followed by in situ epitaxial growth within the etched cavities. Localized strain accumulated inside the crystal serves as the fundamental driving force for etching. Geometric phase analysis of high‐resolution transmission electron microscopy images shows that the strain distribution becomes more uniform after etching. First‐principles calculations indicate that both tensile and compressive strains increase the lattice energy and reactivity, and that the etched edges stabilize at a thermodynamically favorable zigzag atomic configuration rather than the armchair configuration, ensuring regular cavities suitable for epitaxy. This mosaic structure effectively relieves the stress caused by lattice mismatch and reduces defect states at conventional heterointerfaces, markedly suppresses non‐radiative recombination, and enables dual‐color or even multi‐color emission. The structure can be directly applied to light‐emitting pixels, multi‐color LEDs, and on‐chip integrated light sources. This method allows the large‐scale fabrication of large‐area, periodic mosaic arrays without the need for lithography and exhibits high tolerance to lattice mismatch. Future work can extend it to more combinations of halide metal ions and use it to construct programmable displays, multi‐channel optical communications, and complex photonic circuits.

3.2.3. 0D/2D Heterostructures

0D/2D perovskite heterostructures refer to a class of mixed‐dimensional heterostructures formed by spatially integrating 0D perovskite nanocrystals with 2D perovskite nanoplates. 0D perovskite quantum dots, with their strong quantum confinement effects and high photoluminescence quantum yields (PLQY), enable narrowband, tunable light emission. However, their soft ionic lattice and dynamic surface ligands make them highly susceptible to phase transitions and chemical degradation under light, heat, and humidity. By constructing 0D/2D heterostructures, the inherent environmental tolerance of 2D perovskites can be imparted to the 0D perovskites. The 2D component acts as a physical protective layer isolating oxygen and moisture, effectively suppressing non‑radiative recombination and material degradation. Therefore, 0D/2D heterostructures represent an important route to enhance the overall stability of perovskite‑based optoelectronic devices.

All‑inorganic CsPbI₃ quantum dots, owing to their excellent thermal stability and size tunability, are highly promising materials for achieving efficient and stable perovskite optoelectronic devices. However, at room temperature this material readily undergoes a phase transition from the photoactive α‑phase to the optically inactive δ‑phase. Conventional surface passivation or polymer encapsulation can delay degradation to some extent, but often at the expense of charge transport performance, and they hardly prevent the phase transition thermodynamically. Therefore, selecting a heteromaterial with good conductivity to directly “lock” the photoactive phase at the heterointerface is an effective strategy to overcome the bottleneck for achieving efficient and stable optoelectronic devices based on this system. Wei et al. successfully constructed a “sandwich‑type” quasi‑2D perovskite/CsPbI₃ quantum dot/quasi‑2D perovskite epitaxial heterostructure by using two organic cations with different steric hindrance to induce two perovskite phases with different dimensional structures, and by manipulating the dipole‐dipole interactions between ligands through tuning ligand polarizability [73]. In this structure, a periodic zigzag epitaxial interface with atomic sharpness and an interfacial gap of only 1.2 nm formed between the quantum dots and the quasi‑2D perovskites on both sides. High‑angle annular dark‑field scanning transmission electron microscopy (HAADF‑STEM) revealed a clear displacement of Cs atoms in the CsPbI₃ quantum dots near the epitaxial interface. This displacement originates from local lattice strain induced by the ordered arrangement of edge‑oriented ligands at the epitaxial interface. The strain causes tilting of the [PbI₆]⁴⁻ octahedra in CsPbI₃, with the tilt angle reaching about 3.6° near the interface. Theoretical calculations show that as the octahedral tilt angle increases, the Gibbs free energy difference between the photoactive α‐CsPbI₃ and the photoinactive δ‐CsPbI₃ also increases, making the α‐to‐δ phase transition thermodynamically unfavorable. By locking the octahedral tilt, the epitaxial strain raises the energy barrier for phase degradation process, thereby stabilizing the CsPbI₃ quantum dots at room temperature. The perovskite quantum dot films obtained through this strategy also exhibit excellent optical properties and environmental stability.

In summary, dimension engineering spatially integrates perovskite materials of different dimensions, fully exploiting the unique performance advantages of each dimension, and has achieved significant progress in developing new materials and synergistically improving device efficiency and stability. However, conventional in situ formation of 2D capping layers via solution processing is plagued by random orientation, poor phase purity and residual ligands. Vapor deposition techniques are largely restricted to the fabrication of vertical heterostructures. Heterostructures prepared by single‐crystal growth hardly suit efficient integration into miniaturized and highly compact optoelectronic devices. Therefore, achieving large‐area, controllable fabrication of high‐quality, device‐compatible perovskite heterostructures will greatly advance the development of perovskite optoelectronic devices.

3.3. Hybrid‐System Heterostructures

Hybrid‐system heterostructures refer to the combination of perovskites with non‐perovskite materials such as traditional 2D materials, colloidal quantum dots, or metal‐organic frameworks. These structures utilize physical blocking, lattice anchoring, and spatial confinement to construct high‐quality heterointerfaces, effectively suppressing perovskite degradation, phase transition, and ion migration, thereby significantly enhancing perovskite stability.

3.3.1. 2D Material/Perovskite Heterostructures

The 2D materials discussed in this section fall into two categories. The first category consists of organic polymer 2D materials, which have dangling‐bond‐free surfaces and form dense films through intermolecular crosslinking and stacking, achieving encapsulation protection via physical blocking. The second category includes conventional inorganic 2D materials, which can form heterointerfaces with perovskites through van der Waals forces. Although the two types of 2D materials differ markedly in chemical composition and structure, both can construct high‐quality heterointerfaces with perovskites, thereby enhancing device stability.

2D organic polymer materials are chemically stable and highly dense, enabling them to resist moisture and oxygen ingress. Consequently, they can form a dense physical barrier on the perovskite surface with minimal thickness [27, 28]. Ritt et al. synthesized free‐standing 2D polyaramid nanofilms (2DPA‐1) via a solution method and directly covered the surface of MAPbI₃ perovskite films using a spin‐coating process [74]. Experiments showed that a 2DPA‐1 coating of only 60 nm thickness reduced the degradation rate of MAPbI₃ in ambient air by a factor of 14, extending the stable lifetime of the perovskite from 3 days to 21 days. This ultra‐low permeability originates from the staggered stacking of 2DPA‐1 nanosheets, which completely eliminates free volume. The 61% pore‐to‐pore misalignment creates the greatest steric hindrance for molecular transport, geometrically blocking direct pathways for gas molecules. Thus, the 2DPA‐1 coating acts as an extremely thin physical barrier that eliminates free volume and blocks the permeation of oxygen and moisture, effectively suppressing the oxidative and hydrolytic degradation of MAPbI₃.

Beyond serving as physical protection layers, 2D organic materials can enable self‐assembled heterostructures through ligand design. Aubrey et al. developed a bifunctional organic molecule‐guided strategy to construct layered perovskite/non‐perovskite heterostructures with atomically flat interfaces (Figure 9a) [75, 76]. In this design, the ammonium group anchors and orders perovskite layers, while the terminal acid group directs the in situ growth of a secondary inorganic sublattice via hydrogen bonding or metal coordination. This results in periodically stacked heterostructures with well‐defined interfaces. Strain analysis shows that lattice mismatch is accommodated through cooperative deformation of adjacent layers, enabling dislocation‐free and dangling‐bond‐free interfaces without strict lattice matching. Such molecule‐templated heterostructures provide a versatile platform for coupling distinct structural and electronic motifs. Building on this concept, Caniglia et al. extended the strategy to incorporate low‐dimensional magnetic sublattices (Figure 9a) [75]. They constructed a heterostructure in which 2D perovskite layers are linked to isolated 1D Cu–Cl spin chains through bifunctional organic cations. Steric hindrance and lattice templating suppress interlayer disorder and stabilize the low‐dimensional sublattice, demonstrating the generality of this approach.

FIGURE 9.

Hybrid‐system heterostructures. (a) Schematic illustration of layered halide perovskite heterostructure [75]. Reproduced with permission [75]. Copyright 2025, American Chemical Society. (b,c) Schematic illustration of TMD/chiral 2D perovskite heterostructure (b), and corresponding polarization‐resolved photoluminescence (PL) spectra (c) [77]. Reproduced with permission [77]. Copyright 2020, American Chemical Society.

In addition, traditional inorganic 2D materials, such as transition metal dichalcogenides (TMDs), possess atomic thickness, dangling‐bond‐free surfaces, and a flexible layered structure. These structural features enable them to form van der Waals epitaxial heterostructures with perovskites. Traditional heteroepitaxy requires the lattice constants of the two materials to be highly matched. Otherwise, dislocations and dangling bond defects are introduced at the interface, severely compromising material stability. 2D transition metal dichalcogenides (e.g., WSe₂) have atomically flat, dangling‐bond‐free surfaces and can couple with perovskites through weak van der Waals forces. This combination is expected to overcome the limitations of lattice matching [78, 79]. Zhang et al. first grew monolayer WSe₂ triangular single crystals on a SiO₂/Si substrate by chemical vapor deposition, and then deposited CsPbI₂Br perovskite onto the WSe₂ surface via vapor‐phase epitaxy [80]. Benefiting from the van der Waals nature of the WSe₂ surface, perovskite preferentially nucleates and grows into well‑defined square single crystals on WSe₂, whereas randomly oriented micron‑sized pyramids form on the bare SiO₂/Si substrate. HR‑TEM reveals that the epitaxial perovskite lattice is intact and dislocation‑free. Compared with perovskite grown directly on SiO₂/Si, the CsPbI₂Br/WSe₂ epitaxial heterostructure exhibits a significantly reduced Urbach energy from 10.4 meV to 6.5 meV, and the surface defect density decreases by approximately a factor of three, indicating a substantial reduction in energetic disorder and trap state density within the material. Weak van der Waals forces enable the formation of atomically sharp interfaces between two materials with poor lattice matching [81]. Van der Waals epitaxy does not require lattice matching and is therefore highly universal, applicable to a wide range of perovskite compositions and 2D material combinations. When chiral perovskites are employed, such TMDs/perovskite heterostructures can exhibit chirality‐induced spin selectivity, thereby enabling spin manipulation (Figure 9b,c) [77]. However, current methods still rely on high‑temperature vapor deposition, which is not yet compatible with large‑area solution‑based fabrication. Nevertheless, this strategy offers a new approach for constructing hybrid‐system heterostructures with atomically sharp, ultra‑low defect interfaces.

3.3.2. CQD/Perovskite Heterostructures

CQDs and perovskites can form coherent or semi‐coherent interfaces through lattice matching. The anchoring effect of the rigid inorganic lattice of CQDs suppresses phase transitions and ion migration in perovskites, thereby significantly enhancing their thermal and environmental stability. Ning et al. were the first to achieve controllable fabrication of heterostructures between PbS colloidal quantum dots and the organic‐inorganic hybrid perovskite MAPbI₃ using a solution method [82]. The Pb‐Pb atomic spacings of the two materials are 5.97 and 6.26 Å, respectively, a difference of only 4.6%, which satisfies the basic conditions for epitaxy. Therefore, the obtained PbS/MAPbI₃ heterostructure is an epitaxial heterostructure. Density functional theory (DFT) calculations further show that the interface formation energy between the PbS (100) plane and the perovskite (110) plane is below 10 meV Å⁻², meaning that this heterostructure is thermodynamically very favorable to form. Experimentally, PbS CQDs embedded in a perovskite matrix exhibit excellent optoelectronic properties. Compared with pure CQD films, the photoluminescence quantum yield of the quantum dots in the composite film is increased by about three orders of magnitude, while the charge transfer efficiency from the perovskite to the CQDs exceeds 80%. These results are attributed to the effective passivation of the quantum dot surface by the perovskite matrix and the excellent carrier transport capability of the perovskite.

The α‐phase of CsPbX₃ perovskites readily transforms into the optically inert δ‐phase at room temperature, greatly limiting their application. Liu et al. tuned the Br/I ratio of the perovskite to reduce the lattice mismatch with PbS CQDs to below 0.2% [83]. Incorporating 13 vol% PbS CQDs extended the stability of CsPbBr₂I perovskite in ambient air at room temperature from 3 days to over 6 months. XRD confirmed that the pure α‐phase was maintained after 6 months. After annealing at 200°C in air for 5 h, the sample without CQDs showed severe phase separation, whereas the absorption spectrum of the CQD‐anchored sample remained almost unchanged. The origin of this stability lies in the formation of an α/δ interface with high formation energy between the CQDs and α‐CsPbX₃, which requires a higher energy barrier to be overcome for the α‐to‐δ phase transition, effectively suppressing the phase transition kinetically.

3.3.3. MOF/Perovskite Heterostructures

MOFs are a category of porous crystalline materials formed by the self‐assembly of metal ions/clusters and organic ligands via coordination bonds [84]. Their regular nanopores enable spatial confinement of guest materials. Meanwhile, functional sites in the framework can interact with ions in perovskites to form chemical bonds [85, 86]. Encapsulating halide perovskites into MOFs to form PeMOF composites significantly enhances the stability of perovskites under conditions such as humidity, temperature, and light exposure.

Constructing MOF/perovskite heterostructures leverages the synergistic mechanism of spatial confinement and chemical passivation to significantly suppress perovskite degradation and enhance its stability under humidity, temperature, and light exposure. Tsai et al. found that confining perovskite nanocrystals within MOF films greatly improves their resistance to ultraviolet radiation, high temperature, and electric field stress [87]. They first prepared a 3D Pb‐MOF film in which lead ions are bridged by carboxylic acid ligands and separated from each other at the framework nodes. When a bromide‐containing precursor solution was introduced, each lead site formed [PbBr₆]⁴⁻ octahedra in situ, which subsequently converted into perovskite nanocrystals, thereby achieving spatial isolation of the nanocrystals within the MOF matrix. Transmission electron microscopy revealed that the MOF, as a light‑colored continuous phase, encases dark MAPbBr₃ nanocrystals with no direct contact between nanocrystals, and the nanocrystal size is controlled within 8–13 nm. This physical isolation effectively suppresses ion migration and nanocrystal fusion in the film. Under continuous ultraviolet irradiation (254 nm), the photoluminescence intensity of the MA‐PeMOF film remained stable for 200 h, whereas the bulk MAPbBr₃ film severely degraded within only 6 h, and commercial CsPbBr₃ quantum dot films lost 80% of their luminescence within 34 h.

In summary, hybrid‐system heterostructures integrate perovskites with functional materials such as traditional 2D materials, colloidal quantum dots, or metal‐organic frameworks. This offers an alternative pathway for perovskite stabilization that does not depend on dimensionality engineering of the perovskites themselves. Traditional 2D material/perovskite heterostructures mainly exploit the dangling‐bond‐free surfaces and atomic‐scale density of traditional 2D materials to form ultrathin barriers via van der Waals forces or physical stacking, offering both physical blocking and interfacial passivation [74, 80, 88]. The advantage of this strategy lies in achieving extremely low water/oxygen vapor transmission rates without sacrificing light absorption, making it suitable for flexible devices. However, large‐area uniform transfer of traditional 2D materials remains challenging, and interfacial contact resistance as well as band misalignment may affect charge extraction. CQDs/perovskite heterostructures, on the other hand, utilize the coherent or semi‐coherent interfaces between rigid inorganic lattices of CQDs and perovskites to produce a lattice‐anchoring effect, significantly raising the phase transition barrier and stabilizing all‐inorganic perovskites at room temperature [83]. Nevertheless, the dispersion uniformity of CQDs in the perovskite matrix is difficult to guarantee; excessive incorporation may introduce additional defect states, and the long‐chain ligands on CQDs may hinder carrier transport. Furthermore, MOF/perovskite heterostructures physically isolate individual perovskite nanocrystals via the spatial confinement of a 3D framework, effectively blocking aggregation and ion migration, and exhibit excellent stability under ultraviolet irradiation and high temperatures. However, the thickness and pore structure regulation of MOF films are relatively complex [87]. Overall, depending on the application scenario and requirements, hybrid‐system heterostructures can complement perovskite/perovskite heterostructures, but their compatibility with large‐area fabrication and the optimization of interface engineering remain key focuses for future research [89].

4. Applications of Perovskite Heterostructures in Optoelectronic Devices

Perovskite heterostructures have been widely used in solar cells, light‐emitting diodes, and photodetectors. In these devices, they synergistically enhance device efficiency and long‐term stability through four core mechanisms: defect passivation, suppression of ion migration, regulation of charge carrier separation and recombination, and blocking of moisture and oxygen (Figure 10) [17, 24, 90].

FIGURE 10.

Applications of perovskite heterostructures in optoelectronic devices. The three panels on the right show a perovskite solar cell (PSC), a perovskite light‐emitting diode (PeLED) [91], and a photodetector (PD) [92], respectively. PeLED reproduced with permission [91] Copyright 2021, Wiley‐VCH GmbH. PD reproduced with permission [92]. Copyright 2020, Springer Nature.

4.1. Photovoltaic Devices

The intrinsic instability of perovskite solar cells originates from their soft lattice nature [93]. Under external stresses such as light, heat, and electric fields, ion migration, phase transitions, and lattice distortion readily activated in the bulk and at grain boundaries [94]. These coupled processes accelerate device degradation. Constructing heterostructures within the perovskite bulk or at grain boundaries has therefore emerged as a key strategy to suppress these degradation pathways [95].

Constructing lattice‐matched heterostructure structures is an effective route to stabilize solar cells. Lin et al. Epitaxially grew a full‐lead wide‐bandgap perovskite on a lead‐tin mixed narrow‐bandgap perovskite to form a 3D/3D heterostructure, utilizing the high migration energy barriers of Pb²⁺ and Sn²⁺ to block interdiffusion [96]. Time‐of‐flight secondary ion mass spectrometry showed that the bilayer structure maintained a sharp compositional interface after 60 days of aging. When this heterostructure was integrated into all‐perovskite tandem solar cells, the devices retained 93% of their initial efficiency after 600 h of maximum power point tracking under 1‐sun illumination, without phase separation in the narrow‐bandgap subcell. This provides a structural stabilization approach for the easily degradable lead‐tin layer in tandem cells. However, the nucleation rates of 2D and 3D phases in tin‐based perovskites differ significantly, which can easily lead to vertical phase separation. To synchronize the nucleation kinetics of the two, He et al. introduced a small amount of Cs⁺ to tune the precursor colloidal size, thereby synchronizing the nucleation kinetics of both 2D and 3D tin halide perovskites and successfully fabricating uniform 2D/3D heterostructure films [97]. With Cs⁺ modification, the 2D phase is uniformly distributed along the film thickness direction, and the vertical orientation of 3D grains is improved. This uniform heterostructure effectively suppresses defects, enhances photoluminescence intensity and carrier lifetime, and reduces trap‐state density. The resulting devices achieved an efficiency of 17.04% and retained 92% of their initial efficiency after 1500 h of continuous operation under 1‐sun illumination.

In addition to 3D/3D heterostructures, 2D/3D heterostructures also exhibit unique stability advantages in perovskite solar cells. This structure can raise the phase transition energy barrier of perovskites through epitaxial strain, thereby suppressing the sudden efficiency drop caused by phase transitions during high‐temperature operation of solar cells. Sidhik et al. used a lattice‐matched BA₂FAPb₂I₇ 2D template to induce epitaxial growth of FAPbI₃, introducing compressive strain that increased the phase transition energy barrier from 0.21 eV to 0.32 eV [98]. Solar cells based on this 2D/3D heterostructure retained up to 97% of their initial efficiency after 1000 h of maximum power point tracking at 85°C, whereas conventional template‐free devices lost more than 50% after only 400 h. This indicates that the introduction of strain raises the phase transition energy barrier, greatly extending the high‐temperature operational lifetime of the devices. In addition to surface epitaxy strategies, in situ epitaxy at the bottom region of the perovskite can also effectively suppress degradation at the bottom grain boundaries. Li et al. added AlCl₃ to the precursor solution, which induced in situ formation of 2D/3D heterostructures at the bottom grain boundaries, increasing the activation energy for ion migration by approximately 40% [99]. This strategy enabled methylammonium‐free perovskite solar cells to retain over 92% of their initial efficiency after 1000 h of damp heat testing at 85°C and 85% relative humidity. Meanwhile, unencapsulated devices maintained 98% of their initial efficiency after 1500 h of maximum power point tracking. These results meet industrial stability requirements and demonstrate the effectiveness of the bottom‐template strategy under realistic operating conditions.

Meanwhile, dense 2D perovskite layers or 2D materials act as physical barriers, blocking halide ion migration within the active layer and thus stabilizing the perovskite lattice. Sidhik et al. used an orthogonal solvent method to non‐destructively grow a phase‐pure 2D perovskite layer (n = 3, thickness ≈ 50 nm) on top of a 3D perovskite [100]. Time‐of‐flight secondary ion mass spectrometry showed that the diffusion flux of iodide ions toward the electron transport layer was reduced by two orders of magnitude. The solar cells retained over 99% of their initial efficiency after 2000 h of continuous maximum power point tracking at 55°C, whereas the control devices lost 25% after only 1000 h. This demonstrates that the dense 2D perovskite layer acts as a physical barrier suppressing iodide ion migration, thus greatly enhancing the long‐term operational stability of the devices. The above work focused on iodide migration in conventional 3D perovskites, whereas wide‐bandgap perovskites face the distinct issue of light‐induced halide segregation. To address this, Wen et al. designed an in situ conversion strategy to generate a quasi‐2D layer with a high n value on the surface of wide‐bandgap perovskites, achieving superior energy level alignment and ion blocking [101]. This layer provides better energy level matching with the 3D layer, facilitating electron extraction. No halide segregation was observed under strong light illumination, whereas the control sample exhibited a clearly iodine‐rich phase. This work overcomes the limitation of conventional post‐treatment that only produces n = 1 layers, fundamentally suppressing light‐induced halide segregation that is unique to wide‐bandgap perovskites. Thanks to this strategy, wide‐bandgap perovskite solar cells retained 95% of their initial efficiency after 1000 h of maximum power point tracking. However, this method involves multiple steps including evaporation, spin‐coating, and annealing. The process complexity is an aspect that needs optimization for future large‐area fabrication. The above studies demonstrate that heterostructures with physical blocking effects can suppress halide ion migration, thereby stabilizing the lattice structure of perovskites. This effect significantly extends the operational lifetime of solar cells under damp heat, thermal cycling, and continuous illumination.

By constructing hybrid‐system heterointerfaces with strong chemical bonding capability, surface defects of perovskites can be effectively passivated and the activation energy for ion migration can be increased, thereby stabilizing the perovskite material. Zai et al. integrated monolayer molybdenum disulfide (MoS₂) on both the top and bottom sides of the perovskite film, utilizing S to form Pb‐S bonds. This bonding reduced the surface defect density by an order of magnitude and raised the activation energy for iodide ions to escape the lattice from 0.35 to 0.52 eV. Benefiting from the suppression of non‐radiative recombination by chemical passivation, the solar cells fabricated in this work lost less than 5% of their efficiency after 1200 h of damp heat testing at 85°C and 85% relative humidity, demonstrating the critical role of strong bonding in long‐term device stability [27]. MoS₂ provides chemical bonding, while another strategy achieves even stronger anchoring through surface chemical modification. Wang et al. treated the perovskite surface with lead(II) thiocyanate (Pb(SCN)₂) to make it lead‐rich, then spin‐coated chlorinated graphene oxide (Cl‐GO) to form Pb‐Cl and Pb‐O bonds [102]. This chemical passivation layer extended the stable storage time of the perovskite in air from three days to 21 days. More importantly, it allowed the corresponding solar cells to retain 90% of their initial efficiency after 1000 h of maximum power point tracking at 60°C, whereas the control devices lost more than 50%. Thus, the strong chemical anchoring strategy significantly enhances the operational lifetime of devices. Chemically passivated heterostructures simultaneously increase the open‐circuit voltage and long‐term photothermal stability of solar cells by reducing interface defect density and ion migration rates. The above works demonstrate excellent device performance under standard damp heat testing, providing a material foundation for subsequent industrial encapsulation.

In addition, hybrid‐system heterostructures can also prevent solar cells from failing due to fatigue under dynamic operating conditions by either rigidly constraining the light‐induced lattice expansion or flexibly buffering the strain generated during thermal cycling. Li et al. combined a monolayer graphene with a poly(methyl methacrylate) (PMMA) polymer and placed this composite on top of the perovskite surface [103]. Here, PMMA acts as an interfacial coupling layer to enhance adhesion between graphene and the perovskite, while the monolayer graphene serves as a rigid capping layer that suppresses the dynamic lattice deformation of the perovskite under illumination. The lattice expansion under light is reduced from 0.31% to 0.08%, and the stress concentration at grain boundaries is lowered from approximately 200 MPa to about 50 MPa. With this composite layer, solar cells retained over 97% of their initial efficiency after 3670 h of maximum power point tracking at 90°C under 1‐sun illumination, fully demonstrating the critical role of suppressing dynamic lattice deformation in extending device lifetime. Unlike rigid constraints, chiral molecules offer a flexible stress‐buffering mechanism. Duan et al. used R/S‐methylbenzylammonium to construct a chiral 2D perovskite capping layer [104]. The helical stacking of chiral molecules endows the interface with unique mechanical properties; the stacking resembles a spring that can reversibly extend and contract to buffer thermal stress during thermal cycling between −40°C and 85°C. Mechanical measurements show that the heterochiral interface, which mixes R‐type and S‐type molecules, has an elastic modulus of 1182 MPa, much higher than that of a homochiral interface. Moreover, the π‐π stacking distance between the benzene rings of different chiral molecules in the heterochiral interface is only 3.63 Å, indicating more compact molecular packing. Solar cells based on this heterochiral heterostructure retained 92% of their initial efficiency after 200 thermal cycles and also maintained 92% after 600 h of damp heat testing at 85°C and 85% relative humidity.

The above heterostructure strategies each have their own emphasis in photovoltaic devices. The chemical passivation strategy reduces defect density through strong chemical bonds, features simple processing and low cost, and is particularly suitable for flexible devices and rapid integration. However, it demands high uniformity over large areas. Strain epitaxy introduces compressive stress via lattice mismatch, significantly raising the phase transition energy barrier and providing outstanding stability under high‐temperature operation, but it relies on vacuum deposition and is relatively expensive. Physical blocking by 2D capping layers effectively suppresses ion migration, offers strong universality, and is suitable for standardized modules; nevertheless, the phase purity and orientation control of the 2D layers still require optimization. Chiral interfaces utilize helical stacking to buffer thermal stress, offering clear advantages in scenarios with large day‐night temperature differences outdoors, but the synthesis cost of chiral molecules is high. Depending on the target operating temperature, fabrication budget, and device architecture, researchers can flexibly choose the most appropriate strategy.

Although significant progress has been made in extending device lifetime through heterostructure engineering, challenges remain in large‐area uniform fabrication, failure mechanisms under combined multiple stresses, and the development of in situ characterization techniques [105, 106]. Future efforts should focus on developing solution‐processable multifunctional heterostructures and large‐area film deposition methods, while also establishing accelerated aging test standards that more closely mimic real operating conditions and developing operando characterization techniques to reveal device failure mechanisms under practical use [107]. In addition, lead‐free alternatives and manufacturing costs deserve attention [108].

4.2. Light‐Emitting Diodes

In the industrialization of PeLEDs, the operational lifetime of devices is often limited by electric‐field‐driven halide ion migration [109]. Long‐range diffusion of ions along the potential gradient disrupts lattice integrity, inducing irreversible phase transitions and spectral shifts. However, the use of heterostructures can synergistically suppress the degradation process through multiple mechanisms, including chemical anchoring of the lattice and passivation of surface defects, thereby effectively breaking through the operational lifetime bottleneck of PeLEDs.

To overcome electric‐field‐driven ion migration in perovskite materials, researchers have attempted to introduce physical barriers to interrupt the pathways of ion migration. Perovskite quantum dots (QDs) play a critical role in light‐emitting diodes due to their high color purity and facile tunability of emission color [110]. However, ions tend to escape from the surface of perovskite QDs, leading to aggregation and device performance degradation [111, 112]. This is a central issue currently limiting their stability. Introducing a 2D matrix provides an effective route to physically block ion migration. Li et al. embedded QDs into a quasi‐2D perovskite matrix to form a 0D/quasi‑2D heterostructure [113]. The quasi‑2D matrix acts as a dense protective shell that physically wraps the QDs, blocking the migration of surface I⁻ ions while suppressing QD aggregation under thermal stress. Surface ion migration is the onset of QD degradation, and the quasi‑2D matrix cuts off this pathway. After heating at 400 K for 210 min, the composite film prepared by this method retained 90% of its emission intensity, compared to only 30% for pure QDs. The resulting near‑infrared LED exhibited an operational stability 6.5 times surpassing the highest previously documented device. This study demonstrates that wrapping QDs with a quasi‑2D matrix effectively suppresses ion migration and thermally induced aggregation, significantly enhancing the thermal stability of the material and the operational lifetime of the device. Accurate regulation of the thickness of the quasi‑2D matrix remains a key aspect for future optimization. The heterostructures described above suppress ion migration through spatial separation and surface wrapping, respectively, indicating that blocking ion diffusion is an effective way to extend the lifetime of PeLEDs. Constructing hybrid‐system heterostructures by introducing non‑perovskite materials can also achieve the mechanism of physically blocking ion migration. Based on this, Zhang et al. attempted to use the nanopores of a Zr‑MOF as a confined growth template to restrict the PbI₂ lattice within the pores, followed by amination treatment to convert it into a perovskite superlattice with tunable photoluminescence [114]. The rigid framework of the MOF physically isolates the perovskite sublattices from each other, blocking direct contact between grains. Such contact is a prerequisite for ion migration, and the MOF framework provides a structural basis for eliminating contact. This superlattice exhibits significantly enhanced structural stability compared to free clusters, offering a new approach for fabricating spectrally stable light‑emitting layers for LEDs. However, MOFs themselves have poor electrical conductivity, which would limit carrier injection when these materials are directly used in electroluminescent LEDs. Therefore, future work needs to optimize MOF conductivity or apply this strategy to protective or isolation layers in LEDs.

Meanwhile, under high current density, carrier leakage is a primary cause of efficiency roll‐off and Joule heat accumulation in LEDs. Conventional CsPbI_3‐xBr_x pure‐red devices suffer from a sharp efficiency drop at high brightness. Using electrically pumped transient absorption spectroscopy, Song et al. identified that the root cause is hole leakage [115]. To address this, they inserted p‐toluenesulfonyl‐L‐arginine (PTLA) molecules into the lattice interior, locally expanding the lattice without disrupting the [PbX₆]⁴⁻ framework, thereby forming a wide‐bandgap barrier region. This wide‐bandgap region creates an energy barrier for holes, confining them within the emission zone and reducing hole leakage into the transport layers, which in turn lowers Joule heating and side reactions under high current density. With this strategy, the device maintained an external quantum efficiency (EQE) of 10.5% at an ultra‐high brightness of 22670 cd m⁻², compared to only 0.7% for the control device. Meanwhile, its operational half‐lifetime (T ₅₀) at a brightness of 100 cd m⁻² reached 127 h. This work breaks the conventional mindset of interface engineering and proposes a strategy for constructing heterostructures within the grain interior without disrupting the 3D perovskite framework.

Surface defects are a major factor contributing to material instability. A feasible and general approach is to construct heterostructures using organic ligands or novel inorganic shells that can interact with the constituents of perovskite materials. Such structures can effectively passivate surface defects in perovskites, thereby further enhancing device stability. Quasi‐2D perovskites suffer from randomly mixed phases, which lead to energetic disorder and surface defects. Peng et al. utilized the hydroxyl anchoring effect of a PEIE/PVK substrate to spontaneously form a vertical heterostructure with a 3D bottom layer and a 2D top layer in a single spin‐coating step [63]. The 2D phase has a deeper valence band, forming a quasi‐Type‐II band alignment with the 3D emission region. Band bending confines holes within the 3D region, preventing them from drifting to the defect‐rich surface. Meanwhile, the 2D capping layer passivates surface traps and lowers non‐radiative recombination. The device exhibits a 3.6‐fold improvement in operational stability compared to the control. This method is extremely simple and highly universal, though the formation of the heterostructure strongly depends on the chemistry of the underlying interface. The above work demonstrates that confining carriers via intragrain barriers or vertical band design can effectively suppress efficiency roll‐off at high brightness. Currently, the dominant approach for achieving high‐purity red and blue perovskite quantum dots (PQDs) is mixed‐halide composition engineering, which inevitably introduces surface defects that drive phase separation, accelerate material degradation, and shorten operational lifetime [110, 116]. To address this bottleneck, Zhang et al. introduced guanidinium hydrobromide (GABr) into the perovskite precursor to self‐assemble a 2D/3D mixed‐phase heterostructure in a one‐step process [117]. The long‐chain insulating ligands in the 2D phase physically block the diffusion of free charges toward defect regions, reducing material degradation caused by charge accumulation. At the same time, GABr passivates surface halide vacancies, lowers trap density, and thus retards the aging process. The operational half‐lifetime of the device in air is extended by a factor of 2.6. This work provides a simple 2D/3D self‐assembly strategy for blue emitters and shows the promise of heterostructures in boosting the stability of blue devices.

In polycrystalline thin films, grain boundaries are prone to ion migration and thermal cracking [118, 119, 120]. Constructing single‐crystal heterostructures without grain boundaries can help mitigate these failure risks dominated by grain boundaries [121, 122]. Yuan et al. pre‐transferred a monolayer graphene onto a sapphire substrate, followed by remote epitaxial growth of a CsPbBr₃ perovskite thin film via chemical vapor deposition. The weak van der Waals interface of graphene not only allows oriented nucleation of the perovskite but also facilitates subsequent mechanical delamination [123]. HAADF‐STEM observations reveal that the lattice is continuous and perfectly aligned, with no obvious grain boundaries or dislocations. This heterostructure structurally mitigates the adverse effects of grain boundaries in polycrystalline films as pathways for ion migration and weak points for thermal cracking, while also helping to block ion diffusion paths and improve thermal stress distribution. Meanwhile, the graphene interlayer relieves lattice mismatch strain and suppresses crack generation under thermal stress. Benefiting from high crystallinity, relaxed strain, and suppressed defect states, the fabricated micro‐LED device achieved a T ₅₀ of 9.5 h at an initial luminance of 1000 cd·m⁻². Compared with polycrystalline film devices, this single‐crystal heterostructure device exhibited an approximately 6‐fold increase in EQE and an order of magnitude higher luminance. The single‐crystal strategy fundamentally addresses the inherent defects of polycrystalline films, but the epitaxial growth and transfer processes are complex and costly. Single‐crystal heterostructures demonstrate that grain‐boundary‐free structures help improve device stability, providing a new avenue for realizing long‐lifetime PeLEDs in the future.

To address issues such as ion migration, carrier leakage, and surface defects in PeLEDs, different heterostructure strategies exhibit distinct application advantages. MOF spatial isolation physically blocks ion inter‐diffusion through a rigid framework, offering excellent spectral stability and suitability for white LEDs and microdisplays. However, as mentioned above, conductive MOF cannot achieve better electrical conductivity and are more suitable as protective/blocking layers. 0D/2D quantum dot embedding uses quasi‐2D matrix encapsulation or epitaxial strain to lock the α phase, achieving ultra‑high brightness stability in near‑infrared and pure‐red LEDs. Nevertheless, matrix thickness control and ligand optimization require further study. Vertical 2D/3D heterostructures spontaneously form band bending via one‑step spin‑coating, featuring extreme process simplicity and high universality, making them suitable for large‑area mass production. However, they are highly dependent on the chemistry of the underlying interface. Single‐crystal remote epitaxy eliminates grain boundary effects, delivering optimal device performance and suitability for ultra‑high‑resolution microdisplays, but the epitaxial transfer is complex and costly. Researchers can weigh the options based on target applications and cost budgets.

In summary, heterostructure design effectively suppresses ion migration, strengthens carrier confinement, and facilitates defect passivation. This combination improves spectral stability, mitigates efficiency roll‐off, and prolongs device lifetime. It therefore provides an effective strategy to address two key challenges in perovskite light‐emitting diodes: phase instability and carrier‐leakage‐driven efficiency loss at high current densities.

4.3. Photodetectors

In weak‐light detection and high‐speed imaging applications, perovskite photodetectors are often limited by low carrier mobility, high dark current noise, and poor long‐term stability. The core reason for poor long‐term stability is that perovskite materials are highly sensitive to moisture and oxygen, making them prone to hydration decomposition and oxidative degradation. Inadequate carrier mobility and high dark current noise directly affect the detection sensitivity and response speed of the devices. Typically, the performance of perovskite photodetectors is evaluated by several key figures of merit: responsivity (photocurrent generated per unit incident power, in A·W⁻¹), specific detectivity (normalized signal‐to‐noise ratio, in Jones), response speed (rise/decay time, in µs or ms), and on/off ratio (ratio of photocurrent to dark current). These metrics directly reflect the sensitivity, weak‐signal detection capability, temporal resolution, and dynamic range of the device.

Perovskite materials are highly sensitive to moisture and oxygen, prone to hydration decomposition and oxidative degradation, which leads to a sharp decline in detector performance. To address this pain point, Khan et al. used inkjet printing and controlled annealing temperature to form in situ a composite thin film of CsPbBr₃ nanocrystals embedded in a Cs₄PbBr₆ protective layer on monolayer graphene [124]. Cs₄PbBr₆ features a 0D crystal structure, a wide bandgap, and hydrophobic properties. The dense Cs₄PbBr₆ matrix not only acts as a physical barrier blocking moisture and oxygen permeation but also passivates surface defects of CsPbBr₃ through a Cs‐rich environment and suppresses halide ion migration between adjacent grains. Moreover, the small lattice mismatch between the two effectively relieves interfacial stress. Thanks to this structure, the as‐fabricated photodetector showed almost no photocurrent decay after six months of storage in ambient air without any encapsulation. Additionally, benefiting from the photogating phenomenon at the perovskite/graphene interface, the device achieved an ultrahigh responsivity of 5.7 × 10⁴ A·W⁻¹, and combined with its ultralow dark current, a specific detectivity as high as 1.03 × 10¹⁶ Jones. Furthermore, introducing hydrophobic chiral organic cations can also effectively enhance the environmental tolerance of perovskites. To overcome the vulnerability of conventional perovskites to water‐induced decomposition, Chen et al. incorporated chiral α‑phenylethylamine (α‑PEA) into the lattice to form a low‐dimensional (α‑PEA)PbI₃ perovskite [125]. The bulky α‐PEA cations strengthen the organic‐inorganic interlayer bonding through steric hindrance and strong interactions. As a result, they reduce the desorption rate of organic cations by six orders of magnitude and greatly delay the degradation of the perovskite in air. The resulting detector operated stably for one month without encapsulation, and due to chirality‐induced optical activity, it enabled direct circularly polarized light detection, achieving a responsivity of 797 mA·W⁻¹ and a specific detectivity of 7.1 × 10¹¹ Jones. This work employed chiral perovskite for direct circularly polarized light detection, with stability far exceeding that of 3D perovskites. However, the addition of chiral molecules often widens the bandgap, limiting the spectral response range. Future work may investigate the incorporation of chiral ligands into narrow‐bandgap perovskites to enable new spin‐dependent or optoelectronic functionalities.

It is worth noting that the heterostructure interface, as a region prone to chemical degradation, has a quality that directly affects the stability of photodetector devices [126]. To address this challenge, researchers have attempted to control crystallization kinetics to obtain atomically clean, low‐defect interfaces. Zhang et al. proposed a Seed‐Substrate Dual Assistance (SSDA) strategy, in which vertical WS₂ nanosheets were treated with ultraviolet light combined with ozone to introduce oxygen‑containing functional groups at their edges, forming hydrophilic nucleation sites. At the same time, CsPbBr₃ seeds were pre‑embedded in the precursor, and a CsPbBr₃ film was grown on the vertical WS₂ nanosheet array [127]. The nucleation sites and seeds work synergistically to lower the nucleation energy barrier. The low barrier induces oriented growth of CsPbBr₃ along the c‑axis, ultimately producing a film with large grains, few grain boundaries, and a dense structure. This microstructure suppresses grain boundary scattering and interfacial non‑radiative recombination, thus greatly enhancing the long‐term storage stability of the detector. Thanks to this strategy, the photodetector retained 85.14% of its initial response after 90 days of storage at room temperature. Meanwhile, the vertical WS₂ array provides fast charge transport channels, endowing the device with a responsivity of 0.503 A·W⁻¹, a specific detectivity of 8.87 × 10¹² Jones, and fast response speeds with a rise time of 4.71 µs and a fall time of 55.9 µs. The SSDA strategy overcomes the difficulty of poor perovskite film crystallization on low‐surface‐energy substrates. Thus, it effectively suppresses the main pathways for moisture/oxygen ingress and ion migration, and significantly improves the long‐term stability of the heterostructure. This method can be extended to other TMD/perovskite systems and is expected to become a standard fabrication process for highly stable detectors. In addition to the crystallization quality of the film itself, the cleanliness of the heterostructure interface is also critical for suppressing dark current and enhancing stability. Liu et al. fabricated a photodetector based on a MAPbBr₃ perovskite single crystal and monolayer graphene [128]. Conventional wet transfer of graphene uses a poly(methyl methacrylate) (PMMA) support layer and deionized water; residual PMMA and water severely damage the perovskite surface, leading to a defect‑ridden interface and accelerated degradation. In this work, polydimethylsiloxane (PDMS) was used instead of PMMA, and saturated MAPbBr₃ solution was used instead of deionized water as the transfer solvent, completely avoiding erosion of the perovskite by polar solvents and achieving an atomically clean, residue‑free MAPbBr₃ single‑crystal/graphene interface. The clean heterointerface greatly reduces the defect state density, thereby lowering trap‐assisted carrier recombination and dark current. This work provides a new approach for the damage‑free transfer of 2D material/perovskite hybrid‐system heterostructures and highlights the critical influence of interface cleanliness on improving stability and suppressing dark current.

Heterostructure design enables multi‐dimensional performance enhancement in photodetectors. First, the physical blocking strategies introduce a dense protective layer that effectively suppress moisture and oxygen ingress, thereby improving operational stability, particularly for outdoor applications. However, increased layer thickness may compromise responsivity. In contrast, chiral heterostructures employ chiral ligands to enable direct circularly polarized light detection, offering new opportunities for polarization imaging and quantum communication, although their widened bandgaps limit spectral coverage. Furthermore, interface orientation control promotes large‐grain growth through seeded crystallization and edge functionalization, which enhances charge transport, leading to faster response and improved long‐term stability. This approach is well suited for high‐speed imaging, but typically requires carefully engineered substrates. Meanwhile, clean‐interface transfer strategies avoid damage from polar solvents, enabling atomically sharp interfaces and substantially reduced dark current, which is advantageous for weak‐light detection. Nonetheless, challenges remain in achieving scalable, large‐area transfer.

5. Outlook and Challenges

Despite significant progress in perovskite heterostructure research, several key challenges remain on the path from laboratory studies to practical applications. The most critical bottleneck is device compatibility [129]. In addition to performance and stability, the environmental impact of lead‐containing perovskites must also be taken into account. Developing lead‐free perovskite heterostructures or adopting reliable encapsulation strategies to prevent lead leakage are key measures for achieving environmentally sustainable development in optoelectronic applications.

5.1. Design and Synthesis of Perovskite Heterostructures

Current research on heterostructures remains heavily dependent on empirical trial‐and‐error strategies, lacking rigorous theoretical guidance to effectively mitigate critical issues including ion migration, phase separation, and interfacial defects [18]. Furthermore, scalable, low‐cost, and highly reproducible fabrication protocols for heterostructure construction remain insufficiently established. As a result, the superior operational performance and stability achieved in small‐area devices can hardly be reproduced in large‐area thin‐film systems [130, 131]. Future advances in this field should prioritize theory‐driven design and the development of versatile solution‐processable fabrication techniques, which enable uniform large‐area deposition and precise in situ interfacial regulation of heterostructures [130, 132, 133, 134, 135].

5.2. Future Trends in Stability Enhancement

Most existing heterostructure designs target only a single environmental stress, whereas actual operating conditions often involve coupled photo‐thermal‐humidity‐electrical stresses [106]. The long‐term stability of devices under multi‐field coupled stresses still falls short of practical application requirements. Due to the lack of in situ and real‐time characterization techniques, the dynamic evolution mechanism of heterostructure interfaces during operation remains unclear [136]. Moreover, there is often a trade‐off between enhancing stability and optimizing optoelectronic performance [137]. Future research should focus on developing heterostructures with intrinsic resistance to coupled stresses, advancing in situ characterization techniques, and establishing design strategies that break the stability‐performance trade‐off through synergistic approaches [138, 139, 140].

5.3. Applications in Optoelectronic Devices

Industrial compatibility remains a major challenge. In the photovoltaic field, due to poor uniformity of heterostructures, the stability improvements achieved in small‐area cells are difficult to replicate in large‐area modules [141]. In the field of light‐emitting diodes, the fabrication processes for heterostructures are poorly compatible with large‐scale display production lines, and the manufacturing costs are high, hindering industrial translation. In the field of photodetectors, stability under complex environments still cannot meet the requirements for extreme operating conditions. To address these issues, it is urgent to develop uniform heterostructure fabrication processes suitable for large‐area devices and to establish a technical system compatible with multiple types of device platforms.

5.4. Exploring New Functionalities in Perovskite Heterostructures

Beyond stability optimization, heterostructures also serve as an important means to endow perovskites with novel optoelectronic functionalities, enabling properties such as polarization response, chiral optics, and anisotropic light absorption [142, 143, 144]. For example, chiral molecule/perovskite heterostructures can be used for circularly polarized light detection, while van der Waals heterostructures enable linearly polarized light sensing [143, 145]. However, research on this functional potential is still in its early stages. Future efforts, while maintaining stability, should focus on exploring structural design strategies for polarization detection, chiral light sources, and anisotropic photodetection, thereby opening up new application spaces in polarization imaging and quantum communication.

6. Conclusions

Perovskite heterostructures have emerged as a powerful approach to stabilize perovskite materials and improve the operational stability of optoelectronic devices. In this Review, we systematically summarize recent advances in structural design, interfacial mechanism, and optoelectronic device applications of perovskite heterostructures. Furthermore, we elaborate on the key challenges and future development directions of state‐of‐the‐art‐perovskite heterostructures. From our perspective, future advances should focus on the theory‐guided heterostructural design, operando characterization techniques, and scalable manufacturing heterostruces strategies. Meanwhile, the exploration of functionalities in perovskite heterostructures, such as polarization, is expected to further accelerate the practical deployment and functional diversification of high‐performance perovskite optoelectronic devices.

Fundings

This work is financially supported by the National Science Fund for Distinguished Young Scholars (Grant No. T2225024), National Natural Science Foundation of China (Grant No. U25A20565), National Natural Science Foundation of China (Grant No. 52502048), Natural Science Foundation of Tianjin Municipality (Grant No. 25JCYBJC00140).

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

Data sharing not applicable to this article as no datasets were generated or analysed during the current study.