Suppressing Interfacial‐Accelerated Degradation in Perovskite Solar Cells via Supramolecular Co‐Assembly

ABSTRACT

Metal halide perovskites exhibit exceptional optoelectronic properties, but the perovskite/organic hole‐transport layer interface often accelerates device degradation under thermal and illumination stress. Single‐component interlayers are insufficient to prevent this coupled interfacial failure, leading to simultaneous destabilization of both the perovskite absorber and doped Spiro‐OMeTAD. Here, we report a carbazole‐derived supramolecular co‐assembly composed of ammonium‐functionalized (CzPACl) and flexible oligo(ethylene glycol) (CzOEG) monomers that simultaneously passivates the perovskite surface and stabilizes the adjacent Spiro‐OMeTAD layer. The resulting nanosheet interlayer suppresses non‐radiative recombination, mitigates ionic migration, and preserves the concentration of Spiro‐OMeTAD radical cations, enhancing interfacial wettability and mechanical compliance. Perovskite solar cells incorporating this co‐assembled layer achieve a power conversion efficiency (PCE) of 25.8% and retain over 90% of their initial efficiency after 1000 h of continuous illumination or over 80% after 1000 h of aging at 85°C. This work highlights supramolecular co‐assembly as a rational strategy to suppress coupled interfacial degradation pathways, providing a general approach for stabilizing perovskite optoelectronic devices.

This schematic illustrates the interfacial architecture of a perovskite device modified by a supramolecular co‐assembly layer beneath Spiro‐OMeTAD. The co‐assembled molecules form a compact, ordered barrier on the perovskite surface, enabling intimate interfacial contact while suppressing structural defects. A key function of this layer is selective transport regulation: it facilitates desired charge transfer across the interface but blocks the downward migration of Li‐salt species from the Spiro‐OMeTAD layer into the perovskite absorber, as indicated by the red cross. By inhibiting ion penetration and stabilizing the interface, the co‐assembly layer helps reduce interfacial degradation and improve operational stability significantly.

1. Introduction

Metal halide perovskites have emerged as promising semiconductors for next‐generation optoelectronic devices due to their outstanding optoelectronic properties and low‐cost solution processability [1, 2, 3, 4]. However, moisture and oxygen ingress, interfacial defects, and thermally induced mechanical strain often accelerate ion migration and phase degradation in perovskite materials, leading to severe performance loss over time [5, 6, 7]. Consequently, developing effective interfacial passivation and stabilization strategies that can withstand operational thermal stress is crucial for achieving durable perovskite devices [8, 9, 10]. Under operational conditions, degradation of perovskite absorbers and instability of doped organic hole‐transport layers are often kinetically coupled at their interface, leading to accelerated performance loss compared to either component alone. Therefore, implementing a robust interfacial layer can markedly mitigate synergistic degradation at device interfaces, thereby enhancing the operational stability of perovskite devices.

Polymer materials are widely employed as interfacial modifiers in perovskite solar cells [11, 12, 13]. However, their poorly defined molecular weights, uncontrollable polydispersity, and high purification costs often compromise reproducibility and long‐term reliability [14, 15, 16]. In addition, polymer residues at the interface can impede charge transport, interfere with perovskite crystallization, and exacerbate defect‐assisted recombination, particularly under thermal stress [17, 18, 19]. Functional supramolecular polymers, assembled through non‐covalent interactions, offer an alternative strategy for interfacial engineering [20, 21]. Owing to their reversible and dynamic packing modes, well‐defined topological organization, and mechanically adaptive architectures, supramolecular polymers are well suited to accommodate interfacial strain, stabilize electronic structures, and maintain interfacial integrity under operational conditions [22, 23, 24, 25]. These features make them promising candidates for fine‐tuning interfacial optoelectronic properties while enhancing device stability [26, 27, 28, 29].

Self‐assembled monolayers (SAMs) represent a representative class of low‐dimensional supramolecular assemblies employed for interfacial modification [30, 31, 32]. Typically composed of small molecules bearing anchoring groups and π‐conjugated aromatic units, SAMs bind to the underlying substrate through chemical anchoring, while lateral π–π interactions drive the formation of an electronically functional interfacial layer. Such molecular‐level interfacial organization is widely recognized as critical for achieving high‐performance perovskite photovoltaic devices [33, 34, 35, 36]. Among them, carbazole‐based SAMs have been extensively explored as hole‐selective layers in inverted perovskite solar cells due to their favorable energy‐level alignment and pronounced interfacial dipoles [37, 38, 39, 40]. However, the formation and stability of carbazole‐based SAMs are highly sensitive to molecular electronic structure, conformational geometry, solvent affinity, and protonic environment [41, 42]. These factors often induce uncontrolled molecular aggregation or structural inhomogeneity at the interface, leading to energetic disorder, impaired charge extraction, and accelerated performance degradation during device operation [43]. Therefore, introducing electrically neutral and structurally complementary co‐assembling monomers provides a rational pathway to regulate interfacial assembly and suppress aggregation‐induced instability in small‐molecule‐based interlayers. Importantly, under thermal and illumination stress, degradation of the perovskite absorber and instability of doped organic hole‐transport layers are often strongly coupled through ion migration and interfacial chemical interactions, necessitating interfacial strategies that can simultaneously regulate both components.

In this work, we report a molecularly engineered supramolecular co‐assembly designed to stabilize the perovskite/hole‐transport layer interface under operational thermal and illumination stress. The carbazole‐derived supramolecular polymer is constructed from two complementary monomers bearing ammonium‐functionalized groups (CzPACl) and flexible oligo(ethylene glycol) side chains (CzOEG), enabling simultaneous regulation of both sides of the interface. At the perovskite surface, the ammonium groups form electrostatic and hydrogen‐bonding interactions with undercoordinated species, effectively suppressing interfacial defect states and non‐radiative recombination. Meanwhile, the electrically neutral ether side chains mitigate electrostatic repulsion between adjacent ammonium cations, facilitating the formation of monolayered nanosheet assemblies with improved wettability and mechanical compliance, thereby enhancing interfacial robustness under thermal stress. Importantly, the carbazole moieties embedded in the co‐assembled structure also interact favorably with the adjacent Spiro‐OMeTAD layer, stabilizing both the neutral molecules and their radical cations and preserving efficient hole transport during prolonged operation. Owing to the intrinsic hole‐transporting nature of carbazole, the interlayer maintains favorable energy‐level alignment with the perovskite valence band. As a result of this synergistic interfacial regulation, perovskite solar cells incorporating the supramolecular co‐assembly achieve a PCE of 25.8% and exhibit exceptional operational stability, retaining 90% of their initial efficiency after 1000 h of continuous illumination and over 80% after more than 1000 h of aging at 85°C. This work highlights supramolecular co‐assembly as an effective strategy for stabilizing coupled interfacial degradation pathways in perovskite optoelectronic devices.

2. Results and Discussion

Carbazolyl‐propylammonium chloride (CzPACl) and methoxyethyl carbazole ethyl ether (CzOEG) were obtained by stepwise synthesis (Supporting Information and Figures S1–S5), and their molecular dimensions were determined from Corey‐Pauling‐Koltu n (CPK) models. The length of CzPACl is ∼1.0 nm, and the length of CzOEG is approximately 1.3 nm (Figure 1a). CzPACl, CzOEG, and their 1:1 mixture were dissolved in isopropanol and deposited onto substrates. After solvent removal, samples representing their aggregated states were obtained. Transmission electron microscopy (TEM) shows the microstructural morphologies of the aggregates and the associated molecular packing arrangements, as illustrated in Figure 1b. In protonic solvents (e.g., methanol and isopropanol), the positively charged ammonium ions in carbazole propylammonium chloride induce electrostatic repulsion, which disrupts the planar assembly of carbazole and leads to the formation of vesicle‐like aggregates. The formation process of the vesicle is illustrated in Figure S6a. Energy‐dispersive x‐ray spectroscopy (EDS) mapping in TEM revealed the spatial distribution of C, N, Cl elements, further confirming that the observed morphology originates from CzPACl (Figure S6c–e). Compared with the rigid segment, CzOEG possesses a bulkier flexible moiety, which weakens its tendency to aggregate and leads to the formation of disordered assemblies. Neutral amphiphilic molecules (CzOEG) are essential to mitigate the strong intermolecular interactions between ionic monomers (CzPACl). Rather than simply disrupting molecular packing, CzOEG acts as a neutral spacer and co‐assembly regulator. In individual CzPACl aggregates, the electrostatic repulsion between adjacent ammonium groups disturbs planar carbazole stacking and promotes curved vesicle‐like assemblies. The introduction of CzOEG spatially separates neighboring CzPA⁺ units, reduces excessive electrostatic repulsion, and provides ether oxygen atoms as hydrogen‐bond acceptor sites. Together with the retained carbazole–carbazole interactions, these effects balance the intermolecular forces and promote the formation of planar nanosheet‐like co‐assemblies. Figure S7 shows that the co‐assembled structures from CzPACl and CzOEG exhibit sufficient mechanical integrity to be suspended on a freestanding carbon grid without any supporting substrate.

FIGURE 1.

The assembly behavior of CzPACl and CzOEG. (a) CPK models of CzPACl and CzOEG. (b) The TEM images of CzPACl aggregates, CzOEG aggregates, and the co‐assembled structures of CzPACl and CzOEG and a schematic illustration of self‐assembled CzPACl, CzOEG, and their co‐assembly. (c) Schematic illustration of the preparation of a monolayer CzPACl‐CzOEG co‐assembly on the substrate. (d) Atomic force microscopy (AFM) images of single‐layer nanosheets assembled from CzPACl and CzOEG. Scale bar: 1 µm. (e) AFM images of molecular clusters obtained by diluting the co‐assembly solution. Scale bar: 5 µm. (f) Interaction structures and binding energies of CzPACl and CzOEG obtained via DFT calculations. (g) ¹H NMR of CzPACl, CzOEG, and their mixture in MeOD‐d₄.

To further verify the co‐assembly, the solution containing co‐assembled species was drop‐cast onto a UV‐ozone‐treated substrate, and the solvent was evaporated to obtain solid‐state co‐assemblies (Figure 1c). By combining CPK modeling with atomic force microscopy (AFM), the thickness of the co‐assembled layered structure was determined to be ∼1.5 nm, corresponding to a monomolecular layer (Figure 1a,d). Therefore, this co‐assembly strategy can effectively suppress the aggregation of CzPACl and promote its better dispersion in organic solvents. Figure S8 shows that the solubility of CzPACl in isopropanol is enhanced in the presence of CzOEG. Upon further dilution of the mixed solution of CzPACl and CzOEG, an aggregated state with cracks was observed in the AFM morphology, while the thickness was still maintained at the monolayer level (Figure 1e).

Density functional theory (DFT) calculations subsequently yielded a binding energy of 𝐸_𝑏 = −0.749 eV between CzPACl and CzOEG (Figure 1f), demonstrating a pronounced intermolecular interaction that stabilizes their co‐assembly. The interactions between CzPACl and CzOEG in solution were also characterized by proton nuclear magnetic resonance (¹H NMR) spectroscopy (Figure 1g). When CzPACl and CzOEG were mixed, the proton signals of the carbazole unit in CzPACl shifted to lower chemical shifts (H₁ from 8.09 to 8.06, H₂ from 7.24 to 7.20, H₃ from 7.46 to 7.44, and H₄ from 7.56 to 7.53), whereas those of the carbazole unit in CzOEG shifted to higher chemical shifts (H_a from 8.02 to 8.04, H_b from 7.15 to 7.16, H_c from 7.38 to 7.40, and H_d from 7.46 to 7.48). This indicates that CzOEG exerted a shielding effect on CzPACl, while CzPACl induced a deshielding effect on CzOEG. Such behavior is consistent with the separation of the NH₃ ⁺ groups in CzPACl. The absorbance spectra further revealed that the absorbance of the mixed solution appeared between those of the individual components, suggesting that the aggregated state of the two aromatic structures tended to converge (Figure S9). The states of CzPACl, CzOEG, and their mixed solutions could be further identified by proton nuclear magnetic resonance diffusion spectroscopy (DOSY) (Figure S10). The diffusion coefficient D is generally determined according to the following Stokes‐Einstein equation (Equation 1):

$$D=\frac{k_{\mathrm{B}}T}{6\pi \eta r_h}$$ (1)

where D is the diffusion coefficient, 𝑘_B is the Boltzmann constant, T is the absolute temperature, η is the viscosity of the solvent, and r _h is the hydrodynamic radius of the diffusing species. The diffusion coefficient of CzPACl in methanol was determined to be 1.09 × 10⁻⁵ cm² s⁻¹, while that of CzOEG in methanol was 1.52 × 10⁻⁵ cm² s⁻¹. In the mixed state, CzPACl and CzOEG exhibited an identical diffusion coefficient of 1.17 × 10⁻⁵ cm² s⁻¹, which further indicates the occurrence of a co‐assembly phenomenon between CzPACl and CzOEG. These results indicate that the CzPACl/CzOEG system does not behave as a simple physical mixture of two independent functional molecules but forms an ordered supramolecular co‐assembled structure. In this co‐assembly, CzOEG acts as a neutral spacer to reduce the electrostatic repulsion between adjacent CzPA⁺ units, while the carbazole backbones and hydrogen‐bonding interactions maintain favorable intermolecular association.

The interactions between supramolecular co‐assemblies and the perovskite were further investigated. As shown in Figure 2a, x‐ray diffraction (XRD) analysis reveals that the supramolecular co‐assemblies react with PbI₂ to form a low‐dimensional perovskite phase. The inset illustrates the proposed low‐dimensional perovskite structures formed between CzPA⁺ and the perovskite. To clarify the individual contribution of each component, additional XRD measurements were performed using CzPACl and CzOEG separately (Figure S11). The CzPACl‐treated sample exhibits a characteristic low‐angle diffraction peak, confirming that the formation of the low‐dimensional perovskite‐related phase is mainly induced by CzPACl. This can be attributed to the ammonium group of CzPA⁺, which strongly interacts with PbI₂/perovskite and serves as an organic spacer. In contrast, CzOEG does not generate a corresponding low‐dimensional phase owing to the absence of an ammonium anchoring group. By adopting the single‐crystal structure of PEA₂PbI₄ as a structural model and correlating it with powder XRD analysis, the interlayer spacing of the resulting CzPA₂PbI₄ phase was determined to be approximately 2.3 nm. DFT calculations reveal strong binding between individual molecules and the perovskite surface, with binding energies of E_b = −3.34 eV for CzPA⁺ and E_b = −2.45 eV for CzOEG (Figure 2b). Scanning electron microscopy (SEM) analysis (Figure 2c) shows that the pristine perovskite surface contains residual defects, whereas CzPA⁺ modification passivates undercoordinated surface sites by forming a thin dielectric layer, leading to reduced secondary electron emission and a darker SEM contrast, although local pinholes and microcracks remain. CzOEG modification promotes surface recrystallization into larger crystalline domains but suffers from local aggregation due to its high molecular mobility. In contrast, the supramolecular co‐assembly forms a uniform and compact interfacial layer, effectively integrating strong chemical passivation with homogeneous surface coverage. Such morphological uniformity is critical for suppressing thermally accelerated interfacial degradation and maintaining structural integrity at the perovskite/HTL interface. Figure 2d–g and Figure S12 present the thermal stability of perovskite films modified with different interfacial layers, monitored by XRD. Before aging, the pristine film exhibits a weak PbI₂ diffraction peak, indicating the presence of residual degradation. In contrast, perovskite films modified with CzPACl, CzOEG, and the supramolecular co‐assembly show a pronounced suppression of the PbI₂ peak, suggesting improved phase purity. Notably, CzOEG‐modified films display the emergence of a minor δ‐phase, which can be attributed to partial local dissolution of the perovskite induced by the flexible ether side chains. After thermal aging at 85°C under illumination (10 mW cm⁻², 0.1 sun) for 500 h, all films exhibit varying degrees of structural degradation, primarily driven by thermally induced stress and the volatilization of perovskite constituents (e.g., I ₂ and organic species). This degradation is reflected by an increased relative intensity of the PbI₂ diffraction peak. Compared with the pristine film, perovskite films modified with CzPACl, CzOEG, and especially the supramolecular co‐assembly show markedly enhanced resistance to thermal degradation. Among them, the co‐assembled interlayer most effectively suppresses PbI₂ formation, highlighting its superior capability to stabilize the perovskite phase under operational thermal stress.

FIGURE 2.

Interactions between the perovskite and supramolecular co‐assemblies. (a) X‐ray diffraction (XRD) patterns of the reaction products formed between the co‐assemblies and PbI₂, as well as between the co‐assemblies and perovskite films. (b) Calculated binding energies of CzPA⁺ and CzOEG with FAPbI₃. (c) Scanning electron microscopy (SEM) images of pristine perovskite and perovskite films modified with CzPACl, CzOEG, and the co‐assembled interlayer, respectively, together with schematic illustrations of the corresponding interfacial passivation mechanisms. Scale bar: 400 nm. (d–g) XRD patterns of perovskite films modified with different passivation layers before and after thermal aging.

Although effective passivation of the perovskite surface is essential for suppressing intrinsic degradation, the operational stability of perovskite solar cells is ultimately governed by the coupled degradation processes at the perovskite/HTL interface. The perovskite/supramolecular co‐assembly/Spiro‐OMeTAD interfaces were investigated by time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). The depth profiles of CzPA⁺, CzOEG⁺, Spiro‐OMeTAD⁺, and Li⁺ across the multilayer stack are shown in Figure 3a,b. CzPA⁺ is predominantly localized at the perovskite/Spiro‐OMeTAD interface, consistent with its strong anchoring interaction with the perovskite surface. In contrast, CzOEG⁺ partially diffuses into the Spiro‐OMeTAD layer, indicating intimate molecular mixing at the upper interface. This selective distribution is governed by the different interfacial binding strengths, polarity, and specific intermolecular interactions of the two components rather than by molecular size alone. The positively charged ammonium group of CzPA⁺ can strongly bind to the ionic perovskite surface through electrostatic interactions and hydrogen bonding with undercoordinated surface species, thereby immobilizing CzPA⁺ at the perovskite interface. By contrast, CzOEG is electrically neutral and contains flexible oligo(ethylene glycol) side chains, which gives it better compatibility with the organic Spiro‐OMeTAD layer. Moreover, favorable interactions between the carbazole unit of CzOEG and Spiro‐OMeTAD further promote partial intermixing in the hole‐transport layer. Notably, the diffusion of Li⁺ toward the perovskite layer is effectively suppressed by the co‐assembled interlayer. Figure 3c schematically illustrates the perovskite/supramolecular co‐assembly/Spiro‐OMeTAD interface, where a fraction of CzOEG selectively diffuses into the Spiro‐OMeTAD layer without penetrating the perovskite. Meanwhile, the dense co‐assembled interlayer effectively blocks Li⁺ migration, preventing its ingress into the perovskite layer. DFT calculations reveal a weak but favorable interaction between CzOEG and Spiro‐OMeTAD, with a binding energy of E _b = −0.058 eV, supporting the formation of a partially mixed interfacial region. Figure 3d presents the ¹H NMR spectra of CzOEG, Spiro‐OMeTAD, and their mixture, providing evidence of molecular‐level interactions between CzOEG and the hole‐transport material. Upon the addition of CzOEG, noticeable peak broadening is observed for the proton resonances of Spiro‐OMeTAD, while the signals of CzOEG shift toward lower chemical shifts, indicating altered local electronic environments arising from intermolecular interactions. Consistently, electron paramagnetic resonance (EPR) spectroscopy reveals an increased radical content in Spiro‐OMeTAD upon incorporation of CzOEG. This enhancement is attributed to the stabilizing interaction between the carbazole units and Spiro‐OMeTAD, in which the conjugated aromatic framework facilitates partial charge delocalization of the radical cations, while the rigid carbazole structure suppresses dynamic quenching processes (Figure 3e). Differential scanning calorimetry (DSC) measurements further show that the addition of CzOEG increases the glass transition temperature T _g of Spiro‐OMeTAD to 105.4°C (102.4°C in the presence of lithium dopants), exceeding typical values reported for pristine Spiro‐OMeTAD (Figure 3f) [44, 45, 46]. Through thermogravimetric analysis (TGA), the decomposition temperatures of CzPACl and CzOEG were found to be 150.3°C each, indicating their high thermal stability (Figure S13). Together, these results demonstrate that controlled molecular intermixing induced by the supramolecular co‐assembly simultaneously stabilizes the electronic and thermomechanical properties of Spiro‐OMeTAD, thereby suppressing interfacial degradation under operational stress.

FIGURE 3.

Interfacial interactions of the supramolecular co‐assembly layer. (a) Depth profiles of CzPA⁺, CzOEG⁺, Spiro‐OMeTAD⁺, and Li⁺ obtained from ToF‐SIMS. (b) ToF‐SIMS depth profiles showing the distribution of FA⁺, Spiro‐OMeTAD⁺, Li⁺, CzPA⁺, and CzOEG⁺ across the perovskite/HTL interface as a function of sputtering time. (c) Schematic representation of the supramolecular co‐assembly at the perovskite/Spiro‐OMeTAD interface, highlighting the selective diffusion of CzOEG into the Spiro‐OMeTAD layer and the suppression of Li⁺ migration, and illustrating the mechanism by which the co‐assembled layer stabilizes the interface. (d) Interaction between Spiro‐OMeTAD and CzOEG, supported by ¹H NMR spectra of CzOEG, Spiro‐OMeTAD, and their mixture, indicating molecular‐level interactions at the interface. (e) Electron paramagnetic resonance (EPR) spectra of Spiro‐OMeTAD with and without CzOEG, showing an enhanced radical cation signal upon incorporation of CzOEG. (f) Differential scanning calorimetry (DSC) curves of Spiro‐OMeTAD with and without CzOEG, illustrating the increase in glass transition temperature (T_g ) and improved thermal stability of the hole‐transport layer.

While the supramolecular co‐assembly effectively stabilizes the perovskite/HTL interface at the structural and chemical levels, it is essential to further elucidate how such interfacial regulation translates into changes in the semiconductor properties and charge‐carrier dynamics of the perovskite absorber. Time‐resolved photoluminescence (TRPL) measurements revealed that the fluorescence lifetime of the interface passivated by the co‐assembled solution was extended to 2.60 µs, exceeding that of the control (pristine film) sample (0.241 µs) (Figure S14). This indicates that the introduction of the co‐assembly layer significantly reduces the recombination centers at the surface of the perovskite film, thereby suppressing non‐radiative recombination. Meanwhile, photoluminescence (PL) mapping was used to characterize the surface density and uniformity of non‐radiative recombination centers in perovskite films modified with the co‐assembly layer. The films with the co‐assembly layer exhibited higher PL intensity. The cumulative distribution function (CDF) indicates that the PL of the modified films is more uniform. These results suggest that the modified perovskite films have a more uniform surface and lower density of non‐radiative recombination centers, consistent with the TRPL measurements (Figures S15 and S16). In addition, transient photovoltage (TPV) measurements indicated that the carrier lifetime after passivation was significantly enhanced, increasing from 46 to 67 µs (Figure S17a). This indicates that the introduction of the co‐assembly layer reduces the density of defects, thereby decreasing the defect‐induced recombination. Admittance spectroscopy was employed to evaluate the trap‐state density of the perovskite films at different energy levels before and after passivation. The defect‐state density of the perovskite films passivated with the co‐assembled layer decreased from 10¹⁴ to 10¹³ cm⁻³ eV⁻¹ at 0.33 eV and 10¹⁵ to 10¹⁴ cm⁻³ eV⁻¹ at 0.5 eV (Figure S17b). Furthermore, space‐charge‐limited current (SCLC) measurements confirmed that the co‐assembled layer more effectively reduced the electron and hole trap‐state densities in the perovskite films. The electron trap‐state densities before and after modification were 3.55 × 10¹⁵ and 1.16 × 10¹⁵ cm⁻³, respectively, while the hole trap‐state densities were 1.16 × 10¹⁵ and 8.87 × 10¹⁴ cm⁻³, respectively (Figure S17c,d).

Having established the structural stabilization and improved charge‐carrier dynamics induced by the supramolecular co‐assembly, we next evaluate how these interfacial advantages translate into the photovoltaic performance of complete perovskite solar cells, as shown in Figure 4a. For the champion solar cell (modified by co‐assemblies) with the co‐assembled passivation layer, an open‐circuit voltage of 1.18 V, a short‐circuit current of 25.80 mA cm⁻², a fill factor of 84.6%, and a PCE of 25.8% were achieved, which were higher than those of the control device (open‐circuit voltage: 1.15 V, short‐circuit current: 25.58 mA cm⁻², fill factor: 81.12%, without treatment). The J–V curve of the champion device is shown in Figure 4b, whereas the statistical box plots of PCE before and after the various passivation treatments are provided in Figure S18. To further clarify the contribution of the individual components, the J–V curves and PCE distributions of devices modified with CzPACl and CzOEG were also compared (Figure S19). Both CzPACl and CzOEG improve the device performance relative to the pristine device, confirming their positive roles in interfacial regulation. Nevertheless, the efficiencies of the individually modified devices remain lower than that of the CzPACl/CzOEG co‐assembled device, highlighting the synergistic advantage of the co‐assembly strategy over the individual components. The integrated current density calculated from the EQE spectrum is 25.0 mA cm⁻² for the control device and 25.3 mA cm⁻² for the target device, consistent with the J–V results (Figure 4c). Owing to the dense molecular packing, high decomposition temperature, and the ability to improve the thermal stability of Spiro‐OMeTAD to a certain extent, the stability of the devices was subsequently evaluated. The co‐assembly passivated solar cells were able to operate stably for over 1000 h while maintaining more than 90% of their maximum power point, which was significantly higher than that of other control devices (Figure 4d). The thermal stability of the devices was also evaluated. Under continuous heating at 85°C, the solar cells passivated by co‐assemblies retained over 80% of their maximum power for more than 1000 h. Under the same conditions, CzPACl maintained 75% of its initial maximum power, whereas CzOEG maintained only 60%, indicating inferior thermal stability (Figure 4e). This co‐assembly passivation strategy is believed to effectively passivate perovskite defects, enhance carrier lifetimes, and improve device performance. Meanwhile, the densely packed molecular arrangement further suppresses interfacial ion diffusion and degradation, thereby contributing to improved device stability.

FIGURE 4.

Performance comparison of PSCs with the control and co‐assembly structures. (a) Device structure illustration of PSCs. (b) Forward and reverse J‐V scans of control and passivation layer treated champion devices. (c) EQE of the champion device and corresponding integrated current density. (d) ISOS‐L‐1 stability of unencapsulated devices modified with different passivants, measured at room temperature under a nitrogen atmosphere. (e) ISOS‐D‐2 stability of unencapsulated devices modified with different passivants under 85°C conditions and nitrogen atmosphere.

3. Conclusion

In summary, we demonstrate a supramolecular co‐assembly strategy that effectively stabilizes the perovskite/organic hole‐transport interface by simultaneously regulating chemical passivation, mechanical compliance, and interfacial charge transport. By co‐assembling two structurally complementary carbazole‐derived monomers, CzPACl and CzOEG, a monolayered nanosheet interfacial layer is formed that anchors strongly to the perovskite surface while remaining electrically and mechanically compatible with the adjacent Spiro‐OMeTAD layer. At the perovskite interface, the ammonium‐functionalized CzPA⁺ units suppress undercoordinated surface defects and inhibit thermally accelerated phase degradation, whereas the incorporation of electrically neutral CzOEG mitigates electrostatic repulsion, promotes ordered interfacial assembly, and enhances mechanical robustness under thermal stress. Importantly, the co‐assembled interlayer also regulates the perovskite/HTL junction by suppressing Li⁺ migration into the perovskite while enabling partial penetration of CzOEG into the Spiro‐OMeTAD layer, where favorable molecular interactions stabilize radical cations, increase the glass transition temperature, and preserve efficient hole transport during prolonged operation. As a result of this synergistic interfacial regulation, perovskite solar cells achieve a high PCE of 25.8% together with exceptional operational stability, retaining over 90% of their initial efficiency after 1000 h of continuous illumination and over 80% after more than 1000 h at 85°C. Beyond performance metrics, this work reveals that accelerated device degradation can originate from coupled interfacial failure processes rather than from the intrinsic instability of individual layers. The supramolecular co‐assembly concept presented here provides a general and modular platform for addressing such interfacial coupling effects, offering a promising pathway toward stable and efficient perovskite optoelectronic devices.

Author Contributions

Boyang Lu: writing – original draft, writing – review and editing, conceptualization, methodology, software, data curation, formal analysis, validation, investigation. Xiaopeng Feng: writing – original draft, writing – review and editing, conceptualization, methodology, software, data curation, formal analysis, investigation, supervision, funding acquisition. Zhipeng Shao: project administration, resources, supervision, writing – review and editing, funding acquisition, visualization. Mingyuan Han: writing – original draft, software, data curation. Xiaofan Du: software, data curation, validation, formal analysis. Qichao Meng: data curation, software, writing – review and editing. Yaliang Han: writing – review and editing, data curation, software, methodology. Rongxiu Liu: writing – review and editing, methodology, software, data curation. Ziqiang Su: formal analysis, writing – review and editing, methodology, software, data curation. Bingqian Zhang: software, data curation, methodology. Hao Wei: writing – review and editing, formal analysis. Zucheng Wu: formal analysis. Changcheng Cui: formal analysis, writing – review and editing. Shengren Xia: formal analysis, writing – review and editing. Fengzhi Jiang: writing – review and editing, resources, project administration, funding acquisition, visualization, supervision, conceptualization. Guanglei Cui: supervision, resources, project administration, funding acquisition, writing – review and editing, visualization, conceptualization.

Conflicts of Interest

The authors declare no conflicts of interest.

Supporting information

The authors have cited additional references within the Supporting Information.Supporting File 1: anie73501‐sup‐0001‐SuppMat.docx.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.