Black Phosphorus Quantum Dots for Sensing and Optoelectronic Applications: From Fundamental Properties to Device Integration

ABSTRACT

Black phosphorus quantum dots (BPQDs) have recently attracted considerable attention as emerging nanomaterials for next‐generation sensing and optoelectronic technologies due to their tunable bandgap, strong light–matter interaction, high carrier mobility, and large surface‐to‐volume ratio. In this review, we systematically summarize recent advances in BPQD‐based sensors and optoelectronic devices, focusing on synthesis strategies, physicochemical properties, and device integration mechanisms that govern their performance. Particular attention is devoted to the roles of BPQDs in electrochemical and optical sensing platforms, where their quantum confinement effects, rich surface chemistry, and efficient charge transfer characteristics enable enhanced sensitivity, selectivity, and signal amplification. In addition, recent developments in optoelectronic applications, especially in organic and perovskite solar cells, are critically discussed, highlighting how BPQDs contribute to improved charge transport, interfacial engineering, and device efficiency. Current limitations associated with environmental instability, large‐scale synthesis, and long‐term operational reliability are also analyzed. Finally, future research directions are proposed to advance the practical implementation of BPQD‐based technologies. To the best of our knowledge, this work represents the first comprehensive review specifically dedicated to BPQD‐based sensors and optoelectronic devices.

Black phosphorus quantum dots (BPQDs) combine tunable bandgaps, high carrier mobility, and strong light–matter interactions, enabling advanced sensing and optoelectronic applications. This review highlights recent progress in BPQD‐based sensors and photovoltaic devices, emphasizing performance enhancement, device integration, current challenges, and future opportunities.

1. Introduction

Two‐dimensional (2D) materials have attracted enormous scientific interest over the past decade due to their unique electronic, optical, and physicochemical properties [1, 2, 3]. Following the discovery of graphene, a wide range of layered materials such as transition metal dichalcogenides (TMDs), hexagonal boron nitride, and black phosphorus (BP) have been explored for applications in electronics, sensing, and energy technologies [4, 5]. Among these materials, BP has emerged as a particularly promising candidate because of its layer‐dependent bandgap, high carrier mobility, and strong in‐plane anisotropic properties [6, 7]. Unlike graphene, which lacks an intrinsic bandgap, BP exhibits a tunable direct bandgap ranging from approximately 0.3 eV in bulk form to about 2.0 eV in monolayers, making it highly attractive for optoelectronic and sensing applications [8, 9].

In recent years, the dimensional reduction of BP into nanoscale structures has opened new possibilities for advanced nanodevices. In particular, black phosphorus quantum dots (BPQDs) have attracted significant attention due to the emergence of quantum confinement and edge effects that further modify their electronic and optical characteristics [10, 11]. Typically ranging from a few to tens of nanometers in size, BPQDs exhibit unique size‐dependent properties including enhanced photoluminescence, tunable optical absorption, large specific surface area, and abundant surface active sites. These characteristics make BPQDs especially suitable for applications where efficient charge transfer, strong light–matter interaction, and high surface reactivity are required [12, 13, 14].

Various synthesis strategies have been developed to produce BPQDs with controlled size, morphology, and surface chemistry. Both top‐down and bottom‐up approaches have been reported, including liquid exfoliation, ultrasonic‐assisted exfoliation, solvothermal synthesis, electrochemical methods, and chemical etching. These techniques allow researchers to tailor the structural and electronic properties of BPQDs to meet the requirements of specific applications. Moreover, surface functionalization and hybridization with other nanomaterials have further expanded the versatility of BPQDs by improving their stability, dispersibility, and interfacial compatibility within device architectures [15, 16, 17].

One of the most promising application areas of BPQDs is in sensing technologies. The large surface‐to‐volume ratio and rich surface chemistry of BPQDs enable strong interactions with target molecules, which can significantly enhance the sensitivity and selectivity of sensing platforms. BPQD‐based materials have been investigated in a wide range of sensing systems, including electrochemical sensors, fluorescence sensors, and photoelectrochemical sensors. These sensors have demonstrated excellent performance in detecting various analytes such as biomolecules, environmental pollutants, gases, and metal ions. The incorporation of BPQDs into sensing platforms can improve electron transfer kinetics, amplify detection signals, and enable low detection limits, making them highly attractive for biomedical diagnostics and environmental monitoring [18, 19, 20].

Beyond sensing, BPQDs have also shown remarkable potential in optoelectronic devices due to their tunable bandgap and strong optical absorption across a broad spectral range. Their excellent charge transport characteristics and efficient interfacial interactions make them promising components in next‐generation optoelectronic systems. In particular, BPQDs have been integrated into devices such as photodetectors, light‐emitting systems, and solar cells. In photovoltaic applications, BPQDs can serve as interfacial modifiers, charge transport materials, or light‐harvesting components, contributing to improved charge separation, reduced recombination losses, and enhanced device efficiency [21, 22].

Despite these promising properties, several challenges still limit the practical application of BPQDs. One of the most critical issues is their susceptibility to oxidation and degradation when exposed to oxygen, moisture, and light, which can significantly affect their long‐term stability and device performance. In addition, the development of scalable synthesis techniques, reliable device integration strategies, and standardized performance evaluation methods remains an important area of ongoing research. Given the rapid progress in this field, a comprehensive understanding of the synthesis methods, fundamental properties, and device applications of BPQDs is essential for further technological development. In this context, the present review provides a systematic overview of recent advances in BPQD‐based sensors and optoelectronic devices [23, 24, 25]. The discussion focuses on the key material properties that govern their performance, the mechanisms underlying sensing and optoelectronic functionalities, and the strategies used to integrate BPQDs into practical device architectures. Finally, the current challenges and future research directions are highlighted to guide the development of next‐generation BPQD‐based technologies [26, 27].

2. Structural Characteristics, Chemical Stability, and Synthesis Strategies of BPQDs

2.1. Crystal Structure and Size‐Dependent Structural Features of BPQDs

BPQDs are zero‐dimensional derivatives of layered BP whose structure originates from the puckered orthorhombic lattice of bulk BP. In this lattice, each phosphorus atom forms three covalent bonds with neighboring atoms, creating a layered configuration composed of corrugated atomic planes. When bulk BP is reduced to nanoscale domains typically below 10 nm, quantum dots with confined dimensions are produced while largely retaining the intrinsic puckered arrangement of phosphorus atoms. However, the reduction in lateral size introduces a high density of edge sites and unsaturated surface atoms that distinguish BPQDs from their bulk counterpart [28, 29].

The morphology of BPQDs is usually quasi‐spherical or slightly anisotropic, depending on the preparation route and exfoliation conditions. High‐resolution transmission electron microscopy (TEM) studies consistently reveal lattice fringes corresponding to the (020) or (040) planes of orthorhombic BP, indicating preservation of crystallinity at the nanoscale. Nevertheless, the small particle size leads to a pronounced increase in surface‐to‐volume ratio, which significantly modifies structural stability and surface reactivity [30, 31]. The edges of BPQDs often contain dangling bonds or defect sites, and these features can influence subsequent chemical interactions with surrounding environments.

Another structural aspect is the thickness of the quantum dots, which generally ranges from a few atomic layers to several nanometers. This ultrathin thickness distinguishes BPQDs from thicker nanosheets and facilitates their dispersion in various solvents or polymer matrices. The lateral dimensions and thickness distribution strongly depend on synthesis parameters such as sonication time, solvent polarity, and precursor quality. Consequently, structural uniformity remains an ongoing challenge in BPQD production [32, 33].

From a materials perspective, controlling the structural characteristics of BPQDs is essential because heterogeneity in size or crystallinity may affect reproducibility in downstream applications. Although numerous studies report narrow size distributions, scalable fabrication methods that simultaneously maintain structural integrity and uniformity remain limited. Therefore, further optimization of synthesis protocols and post‐processing techniques is required to achieve consistent BPQD architectures suitable for advanced technological applications [34, 35].

Figure 1 provides detailed structural characterization of BPQDs. Panel 1a shows a low‐magnification TEM image revealing their quasi‐spherical morphology, while panel 1b presents an HRTEM image with clear lattice fringes. The enlarged lattice region in panel 1c displays interplanar spacings corresponding to the (040) and (111) facets, confirming preserved orthorhombic crystallinity. Panel 1d shows the corresponding FFT pattern, further verifying lattice ordering. Panel 1e presents the particle size distribution, with an average diameter of 2.7 ± 0.1 nm. Raman spectra in panel 1f exhibit the characteristic A1g, B2g, and A2g vibrational modes of BP. Finally, panel 1g shows an optical photograph of the exfoliated BPQD dispersion in NMP, illustrating a uniform and stable colloidal solution.

FIGURE 1.

Structural characterization of BPQDs: (a) TEM image showing quasi‐spherical morphology; (b) HRTEM image; (c) lattice fringes of (040) and (111) planes; (d) FFT pattern confirming crystallinity; (e) size distribution (2.7 nm); (f) Raman modes A1g, B2g, and A2g; (g) optical image of BPQDs dispersed in NMP. Reproduced from ref. [34] under the Creative Commons Attribution (CC BY) License. 2017 Advanced Science.

2.2. Surface Chemistry and Chemical Stability of BPQDs

One of the most critical considerations in the practical utilization of BPQDs is their chemical stability. Unlike many other 2D materials, BP is intrinsically susceptible to oxidation when exposed to oxygen, moisture, or light. This instability becomes even more pronounced at the quantum‐dot scale because of the dramatically increased surface area and the presence of reactive edge atoms. As a result, BPQDs tend to undergo gradual oxidation, forming phosphorus oxides or oxyacids that can alter their structural integrity [36, 37].

The oxidation process typically initiates at defect sites or edges where unsaturated phosphorus atoms interact with oxygen molecules. Subsequent reactions with water molecules may accelerate degradation, producing phosphate‐related species and eventually leading to structural fragmentation. Experimental observations have shown that prolonged exposure to ambient conditions may reduce the crystallinity of BPQDs and modify their surface chemistry [38, 39]. Therefore, maintaining chemical stability represents a fundamental challenge in the storage and utilization of these nanomaterials.

To mitigate degradation, several stabilization strategies have been explored. Surface passivation using organic molecules, polymers, or inorganic shells can create protective barriers that reduce direct contact with oxygen and water. Encapsulation within matrices such as polymers, silica, or layered materials has also proven effective in slowing oxidative reactions. In addition, solvent environments and inert atmospheres are commonly employed during synthesis and storage to minimize degradation pathways [40, 41]. Despite these efforts, achieving long‐term stability without compromising intrinsic properties remains difficult. Some passivation methods may introduce impurities or alter surface states, which could influence material performance in subsequent device architectures. Consequently, the design of stabilization approaches must carefully balance protection with preservation of the intrinsic characteristics of BPQDs [42, 43, 44].

Overall, chemical stability remains a central issue in the development of BPQD‐based technologies. Continued research focusing on surface chemistry control, protective coatings, and environmentally robust storage methods is necessary to ensure reliable performance and long‐term durability of BPQD materials [45, 46].

Beyond the qualitative description of oxidation, understanding the degradation kinetics of BPQDs is essential for developing effective stabilization strategies. Current studies suggest that degradation is initiated preferentially at edge and defect sites where unsaturated phosphorus atoms exhibit higher chemical reactivity. The adsorption of oxygen molecules can generate reactive oxygen species, particularly superoxide radicals, which subsequently attack P–P bonds and trigger progressive oxidation. The process is further accelerated in the presence of moisture, resulting in the formation of phosphorus oxides and phosphate‐containing species. Theoretical investigations indicate that different edge configurations may exhibit distinct oxidation susceptibilities, with certain edge sites acting as preferential initiation points for degradation. As oxidation propagates from the surface toward the interior of the quantum dot, electronic states are progressively altered, leading to band structure distortion, fluorescence quenching, and reduced charge transport efficiency. These observations highlight the need for kinetic studies capable of correlating degradation rates with BPQD size, defect density, edge chemistry, and environmental conditions.

Table 1 highlights that no single stabilization strategy simultaneously maximizes environmental durability and preserves the intrinsic optoelectronic properties of BPQDs. In general, stronger protection against oxidation is often accompanied by reduced carrier transport efficiency or increased interfacial resistance. This trade‐off explains why long‐term stabilization remains a central challenge in BPQD research and underscores the need for standardized testing protocols that evaluate both degradation kinetics and device performance under identical environmental conditions.

TABLE 1.

Representative stabilization strategies for BPQDs, their effects on degradation resistance, and associated performance trade‐offs.

Stabilization strategy	Protection mechanism	Typical stability improvement	Impact on electronic/optical properties	Main limitation
Polymer encapsulation (PEG, PVP, PMMA)	Physical barrier against oxygen and moisture	~10–50× longer ambient lifetime	May reduce charge transport and carrier extraction efficiency	Increased interfacial resistance
Silica (SiO2) coating	Dense inorganic shell preventing oxidation	~50–100× improvement in storage stability	Preserves fluorescence but may hinder charge transfer	Additional fabrication complexity
Metal‐oxide shells (Al2O3, TiO2)	Surface passivation and oxygen blocking	~100× improvement under illumination and humidity	Possible band misalignment and reduced carrier mobility	Interfacial energy barriers
Covalent surface functionalization	Saturation of reactive edge sites	~10–30× increase in oxidation resistance	Can modify surface states and optical transitions	Potential alteration of intrinsic properties
2D Heterostructure encapsulation (graphene, h‐BN, MXenes)	Physical protection and charge redistribution	Up to two orders of magnitude reported in some studies	Often maintains charge transport pathways	Complex fabrication and scalability challenges
Inert atmosphere storage and processing	Minimizes oxygen and water exposure	Effective during synthesis and storage only	Negligible effect on intrinsic properties	Not suitable for practical operation
Hybrid polymer/inorganic coatings	Combined moisture and oxygen barrier	Among the highest reported long‐term stability improvements	Better balance between protection and performance	Multistep processing

2.3. Liquid‐Phase and Top‐Down Synthesis Methods

Among the various synthesis approaches developed for BPQDs, top‐down strategies derived from bulk BP remain the most widely used due to their relative simplicity and scalability. Liquid‐phase exfoliation is the most common technique within this category. In this process, bulk BP crystals are dispersed in suitable solvents and subjected to ultrasonication, which generates shear forces capable of breaking the layered structure into smaller fragments and eventually producing nanoscale quantum dots [47, 48, 49, 50].

The choice of solvent plays a crucial role in determining the efficiency of exfoliation and the stability of the resulting BPQDs. Polar aprotic solvents such as N‐methyl‐2‐pyrrolidone (NMP), dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) are frequently employed because their surface energies match that of layered BP, facilitating effective exfoliation and dispersion. Controlled sonication parameters—including power, duration, and temperature—are also essential factors influencing particle size distribution and yield. Another top‐down approach involves electrochemical exfoliation, where bulk BP is used as an electrode in an electrochemical cell. Under an applied voltage, ions intercalate into the layered structure, weakening interlayer interactions and enabling the formation of nanoscale fragments. This method can produce relatively high yields and allows partial control over particle size by adjusting electrolyte composition and electrochemical conditions [51, 52, 53].

Mechanical or chemical milling techniques have also been explored to reduce BP crystals into smaller particles, although these methods may introduce structural defects or impurities. Therefore, post‐processing steps such as centrifugation, filtration, or size‐selective precipitation are commonly used to isolate quantum dots with narrower size distributions. Despite their practicality, top‐down methods often suffer from limited control over particle uniformity and thickness. In addition, prolonged sonication may accelerate oxidation, particularly when carried out in oxygen‐containing environments. Consequently, while top‐down strategies provide convenient access to BPQDs, further refinement is required to achieve precise structural control and reproducibility suitable for advanced material applications [54, 55, 56, 57].

2.4. Bottom‐Up and Chemical Synthesis Approaches

In contrast to top‐down techniques, bottom‐up synthesis strategies aim to construct BPQDs from molecular or atomic precursors through controlled chemical reactions. These approaches have attracted growing attention because they offer the potential for improved control over particle size, crystallinity, and surface composition. Although still less developed than exfoliation methods, several promising bottom‐up routes have been reported [58, 59].

One representative approach involves solvothermal or hydrothermal synthesis, where phosphorus‐containing precursors undergo controlled chemical reactions in sealed reactors at elevated temperature and pressure. Under appropriate conditions, nucleation and growth processes can lead to the formation of nanoscale phosphorus domains that resemble quantum dots. Reaction parameters such as precursor concentration, solvent type, temperature, and reaction time significantly influence the resulting particle size and morphology [60, 61].

Another emerging strategy utilizes chemical vapor deposition or vapor‐phase reactions to generate phosphorus nanostructures on substrates, followed by controlled fragmentation into quantum dots. Although these techniques are more commonly used for thin‐film growth, adapting them for quantum‐dot formation may enable improved control over crystallinity and purity. Microwave‐assisted synthesis has also been explored as a rapid bottom‐up method. Microwave irradiation can accelerate nucleation and growth processes, leading to relatively uniform nanoparticles within short reaction times [62, 63]. However, achieving precise structural characteristics remains challenging because the nucleation mechanisms of phosphorus species in solution are not yet fully understood. Despite their potential advantages, bottom‐up methods currently face several limitations, including complex reaction pathways, limited precursor availability, and difficulties in achieving high yields. Moreover, controlling the crystalline phase and preventing unwanted oxidation during synthesis remain significant challenges [64, 65].

Consequently, while bottom‐up synthesis provides an attractive route toward precisely engineered BPQDs, further mechanistic understanding and methodological optimization are necessary before these approaches can rival the scalability and practicality of established top‐down techniques. Continued exploration of innovative chemical routes may ultimately enable more reliable and controllable production of BPQDs for future technological applications [66, 67].

Table 2 summarizes representative synthesis approaches, structural characteristics, and stability considerations of BPQDs reported in recent studies. Both top‐down and bottom‐up strategies are included to highlight differences in particle size control, crystallinity, and surface chemistry. Top‐down methods such as liquid‐phase and electrochemical exfoliation remain the most widely used due to their relative simplicity and scalability, whereas bottom‐up approaches offer improved structural tunability but often involve complex reaction pathways. Understanding these synthesis routes is essential for tailoring BPQD properties for sensing and optoelectronic applications.

TABLE 2.

Representative synthesis strategies, structural features, and stability considerations of BPQDs.

Synthesis method	Principle of method	Typical size range (nm)	Structural features	Advantages	Limitations
Liquid‐phase exfoliation	Ultrasonic exfoliation of bulk BP in suitable solvents	2–10	Preserved orthorhombic lattice; few‐layers thickness	Simple, widely used, scalable	Broad size distribution, oxidation risk
Electrochemical exfoliation	Ion intercalation under applied voltage weakens interlayer interactions	3–8	High crystallinity with exposed edge sites	Higher yield, controllable parameters	Electrolyte residues, partial structural defects
Mechanical milling	Physical fragmentation of bulk BP into nanoscale domains	5–15	Irregular morphology; increased defect density	Low cost, simple equipment	Structural damage and impurities
Chemical etching	Chemical reactions selectively reduce bulk BP to nanoscale fragments	3–10	Reactive surface atoms and abundant edge states	Tunable particle size	Possible contamination and oxidation
Solvothermal synthesis	Controlled nucleation and growth of phosphorus species in solvent under heat/pressure	2–8	Relatively uniform nanocrystals	Good size control	Complex reaction pathways
Hydrothermal synthesis	High‐temperature aqueous reaction forming nanoscale phosphorus domains	3–10	Layered crystalline domains	Environmentally friendly solvent system	Limited yield and crystallinity control
Microwave‐assisted synthesis	Rapid nucleation induced by microwave irradiation	2–6	Small and relatively uniform particles	Short reaction time	Mechanism not fully understood
Vapor‐phase synthesis	Formation of phosphorus nanostructures followed by fragmentation into quantum dots	2–7	High crystallinity with ordered lattice planes	High purity materials	Complex equipment
Chemical reduction routes	Reduction of phosphorus‐containing precursors to form nanoscale clusters	3–9	Tunable surface chemistry	Flexible chemical design	Precursor limitations
Hybrid synthesis strategies	Combination of exfoliation and chemical treatments	2–10	Tailored surfaces and improved dispersibility	Enhanced functionalization capability	Multistep processing

3. Electronic Structure, Charge Transport Mechanisms, and Optical Dynamics in BPQDs

3.1. Electronic Band Structure and Quantum Confinement Effects

The electronic structure of BPQDs is fundamentally governed by the intrinsic anisotropic lattice of phosphorus and the strong quantum confinement induced by nanoscale dimensions. In contrast to bulk BP, which exhibits a thickness‐dependent but relatively continuous band structure, the reduction of lateral size to the quantum‐dot regime introduces discrete energy levels. This confinement alters the distribution of electronic states and leads to size‐dependent modulation of the bandgap. As the dimensions of BPQDs decrease, the bandgap typically widens due to enhanced confinement of charge carriers [68, 69].

Another distinctive feature of BP‐derived nanostructures is the anisotropy inherited from the puckered atomic configuration. The armchair and zigzag crystallographic directions exhibit different electronic responses, which can influence carrier mobility and density of states. At the quantum‐dot scale, this anisotropy may become partially averaged because of the reduced domain size; however, theoretical calculations indicate that remnants of directional electronic behavior can still persist, especially in larger dots or those with anisotropic shapes [70, 71].

Quantum confinement also modifies the distribution of edge states. Because a significant fraction of atoms in BPQDs reside at the surface or edges, localized electronic states can appear near the band edges. These states may influence carrier localization and recombination processes. While such states can enhance interactions with surrounding environments, they may also introduce trap‐mediated processes that reduce electronic efficiency in certain device architectures [72, 73].

From a critical perspective, theoretical descriptions of BPQD electronic structures remain somewhat inconsistent with experimental observations. Although density functional theory calculations frequently predict pronounced size‐dependent bandgap tuning and well‐defined quantum‐confinement effects, experimentally measured electronic and optical properties often exhibit substantial deviations. Several factors may contribute to this discrepancy. First, most theoretical models consider idealized BPQDs with atomically perfect structures, whereas experimentally synthesized BPQDs typically contain defects, edge irregularities, and partial oxidation. The formation of phosphorus oxide species and associated surface states can significantly modify electronic structures and carrier dynamics. Second, edge effects become increasingly important at the quantum‐dot scale because a large fraction of atoms reside at boundaries, yet edge reconstruction and oxidation are often simplified in theoretical treatments. Third, many computational studies neglect environmental influences such as solvent interactions, adsorbed molecules, and substrate effects, all of which may alter the observed electronic behavior [69, 70, 71]. Furthermore, conventional density functional approaches may inadequately describe excitonic effects and many‐body interactions that become increasingly important under strong quantum confinement. Consequently, future theoretical efforts should move beyond idealized models and incorporate realistic defect populations, surface adsorbates, oxidation states, and environmental effects. Combining advanced ab initio simulations with systematic experimental characterization will be essential for bridging the current theory–experiment gap and establishing predictive models for BPQD‐based electronic and photonic systems [74, 75, 76].

Figure 2 illustrates the size‐dependent optical properties of BPQDs through calculated absorption and emission spectra. Panels 2a and 2c present the absorption spectra of BPQDs with different sizes, showing two dominant absorption peaks across the 300‐ to 700‐nm region. As the quantum dot size increases, the main absorption peak gradually red‐shifts, reflecting bandgap modulation induced by quantum confinement. Panels 2b and 2d display the corresponding emission spectra. For smaller BPQDs (0.8–1.8 nm), the emission peaks exhibit a blue‐shift with increasing size, whereas for larger dots (1.8–3.8 nm), a typical red‐shift is observed. These spectra were calculated from optimized ground and first excited singlet states and broadened using Lorentzian functions (0.25 eV), illustrating the strong size‐dependent electronic and optical behavior of BPQDs.

FIGURE 2.

Size‐dependent optical spectra of BPQDs. (a,c) Calculated absorption spectra and (b,d) emission spectra for BPQDs with different sizes. The spectra, broadened using a 0.25‐eV Lorentzian function, show two main absorption peaks and size‐dependent shifts, reflecting quantum confinement effects and bandgap modulation in BPQD systems. Adapted with permission from ref. [12]. 2016 American Chemical Society.

3.1.1. Origin of Strong Light–Matter Interaction in BPQDs

One of the most frequently cited advantages of BPQDs is their strong light–matter interaction, which originates from the combined effects of quantum confinement, excitonic behavior, and size‐dependent modification of electronic states. When the dimensions of BP are reduced to the quantum‐dot regime, the spatial confinement of charge carriers leads to the formation of discrete energy levels and enhanced overlap between electron and hole wavefunctions. This confinement increases the probability of optical transitions and can strengthen the oscillator strength associated with excitonic excitations.

Compared with bulk BP and larger phosphorene nanosheets, BPQDs often exhibit enhanced exciton binding energies due to reduced dielectric screening and stronger Coulomb interactions between electrons and holes. The increased stability of excitonic states promotes efficient light absorption and radiative recombination processes, which contribute to the observed size‐dependent photoluminescence behavior. Furthermore, quantum confinement modifies the density of optical states near the band edges, leading to stronger absorption features and tunable optical responses across a broad spectral range [75, 76, 77].

The large surface‐to‐volume ratio of BPQDs also facilitates interaction with electromagnetic fields and surrounding chemical species, which is particularly beneficial for sensing applications. In fluorescence‐based sensors, the strong optical response enables sensitive signal transduction and efficient modulation of emission intensity. Similarly, in photodetectors and photovoltaic devices, enhanced optical absorption combined with efficient exciton generation can improve photoresponse and charge‐generation efficiency. Therefore, the strong light–matter interaction in BPQDs should not be viewed as a single material property but rather as the collective consequence of quantum confinement, enhanced excitonic effects, modified optical density of states, and efficient optical transitions. These features provide the fundamental basis for the superior performance of BPQDs in sensing and optoelectronic applications.

3.2. Charge Transport Mechanisms in BPQD Systems

Charge transport in BPQDs differs fundamentally from that of bulk semiconductors because the nanoscale size introduces discrete energy levels and numerous interfaces. In extended crystalline materials, charge carriers typically move through band‐like transport governed by delocalized electronic states. In contrast, BPQDs frequently exhibit transport dominated by inter‐dot interactions, localized states, and energy barriers at interfaces. As a result, carrier migration in BPQD assemblies is often described by hopping or tunneling mechanisms between adjacent quantum dots [77, 78].

The efficiency of this transport strongly depends on the coupling between neighboring dots and the surrounding medium. When BPQDs are well connected within a conductive network or matrix, electronic coupling may facilitate relatively efficient carrier migration. However, weak coupling or large interparticle spacing can introduce substantial resistance to carrier movement. The presence of defects, surface states, or trap sites can further complicate transport by capturing carriers and delaying their movement across the material [79, 80].

Another important factor is the energetic alignment between BPQDs and adjacent materials within a heterostructure or composite system. Misalignment of energy levels can create potential barriers that impede carrier injection or extraction. Conversely, favorable alignment may promote directional carrier transfer and improve overall transport efficiency. Because BPQDs possess size‐dependent energy levels, even small variations in particle size distribution may produce significant changes in interfacial energetics [81, 82].

Critically, the interpretation of charge transport in BPQD‐based systems remains challenging due to the coexistence of multiple transport pathways. Experimental measurements often reflect a combination of hopping, trap‐assisted conduction, and thermally activated processes rather than a single dominant mechanism. Consequently, simplified models may fail to capture the full complexity of carrier dynamics. Future studies should emphasize systematic investigations that correlate structural uniformity with transport measurements. Such efforts could clarify the relative contributions of different transport mechanisms and support the development of predictive models for BPQD‐based electronic materials [83, 84].

3.3. Interfacial Physics and Carrier Transfer Dynamics

Interfaces play a decisive role in determining the behavior of quantum‐dot systems, and BPQDs are no exception. When incorporated into composite structures or device architectures, these nanomaterials inevitably interact with surrounding matrices, electrodes, or other nanostructures. At these boundaries, differences in work function, electronic energy levels, and chemical potential generate interfacial electric fields that strongly influence carrier transfer processes [85].

One key aspect of interfacial physics is the formation of energy barriers or junctions that regulate the flow of electrons and holes. Depending on the relative energy alignment between BPQDs and adjacent materials, carriers may experience either favorable transfer pathways or resistive barriers. Efficient interfaces typically promote rapid separation and directional movement of carriers, whereas poorly engineered interfaces can lead to recombination or energy loss [86, 87].

Surface states located at BPQD boundaries also contribute significantly to interfacial dynamics. These states may act as intermediate energy levels that facilitate carrier transfer across interfaces. However, they can also function as recombination centers if they capture carriers without enabling subsequent transport. The dual role of surface states represents a persistent challenge in optimizing BPQD‐based materials. Another factor influencing interfacial behavior is the presence of local electric fields arising from charge redistribution at material boundaries. Such fields can modify carrier trajectories and affect the efficiency of carrier separation processes. In nanoscale systems, even minor variations in interface quality or chemical composition may lead to substantial differences in carrier transfer dynamics. From a critical standpoint, experimental characterization of interfacial phenomena in BPQD systems remains limited. Techniques such as transient spectroscopy, photoelectron spectroscopy [88, 89, 90].

4. Critical Review of Experimental Studies on BPQDs in Sensors and Optoelectronic Devices

4.1. BPQD–Carbon Hybrid Architectures for Electrochemical Energy Storage

Hybrid nanostructures integrating BPQDs with conductive carbon frameworks have been investigated as a strategy to address the intrinsic limitations of bulk BP in electrochemical systems. A representative study demonstrated the molecular‐level distribution of BPQDs on nitrogen‐doped graphene nanosheets, forming a van der Waals heterostructure designed to enhance lithium storage performance [91]. In this configuration, the nanoscale dimension of BPQDs provided a high density of electrochemically active sites while simultaneously shortening lithium‐ion diffusion pathways. The resulting electrode exhibited a reversible capacity of 1271 mA h g⁻¹ at 500 mA g⁻¹, highlighting the significant electrochemical advantage of the hybrid architecture compared with conventional BP electrodes.

A critical factor in this system is the homogeneous dispersion of BPQDs across the graphene substrate. Molecular‐level distribution suppresses particle aggregation during repeated lithiation–delithiation cycles, which is a common degradation mechanism in phosphorus‐based anodes. The nitrogen‐doped graphene matrix additionally serves as a conductive network that facilitates electron transport while buffering the mechanical stress caused by the large volume expansion associated with the formation of Li₃P. These synergistic effects collectively contribute to improved cycling stability and enhanced electrochemical kinetics [91].

Despite these improvements, several limitations remain. Although the capacity obtained is substantially higher than that of many conventional carbonaceous anodes, it still falls significantly below the theoretical capacity of BP (2596 mA h g⁻¹). This discrepancy suggests that not all phosphorus atoms participate effectively in reversible electrochemical reactions, possibly due to incomplete utilization of active sites or partial structural degradation during cycling. Furthermore, the long‐term structural stability of BPQDs under continuous electrochemical operation remains insufficiently explored.

From a broader perspective, the study illustrates how nanoscale engineering and heterostructure design can mitigate the inherent drawbacks of phosphorus‐based materials. However, the scalability of such molecular‐level assembly strategies and their compatibility with industrial electrode fabrication processes remain open questions. Consequently, further research is required to balance structural control, electrochemical efficiency, and large‐scale manufacturability when integrating BPQDs into advanced energy storage systems.

Although the reported reversible capacity is impressive, it corresponds to only approximately 49% of the theoretical capacity of BP. This discrepancy suggests that significant limitations remain in achieving full utilization of phosphorus active sites. Possible bottlenecks include incomplete lithiation, irreversible side reactions, continuous solid‐electrolyte interphase (SEI) formation, and structural degradation during repeated cycling. Furthermore, the relative contributions of BPQDs and the graphene framework to the observed electrochemical performance remain difficult to distinguish. Future studies should combine operando characterization and mechanistic modeling to identify the dominant capacity‐loss pathways and establish rational design principles for maximizing active‐material utilization.

4.2. BPQD‐Based Nanohybrids for Electrochemical Toxin Sensing

Electrochemical sensing platforms utilizing BPQD‐based nanohybrids have attracted attention for detecting toxic contaminants in food systems. One approach employed a 0D/1D nanohybrid composed of BPQDs anchored onto carboxylated multiwalled carbon nanotubes (CNTs‐COOH) to construct an electrochemical sensor for ochratoxin A (OTA) detection [92]. The integration of BPQDs with the CNT network was achieved through a sonication‐assisted assembly process that enabled strong covalent interactions between the two components. This structural coupling significantly enhanced electrical conductivity while improving the chemical stability of the hybrid material.

The resulting sensing platform exhibited high electrochemical activity and strong resistance to electrode fouling, which is a common limitation in OTA detection due to the complex molecular structure of the toxin. Under optimized conditions, the sensor demonstrated a wide detection range from 0.4 to 10 μM and achieved a limit of detection of 0.03 μM [92]. The system also displayed good reproducibility and satisfactory anti‐interference capability when tested in complex sample matrices. Importantly, recovery results obtained from agricultural crop samples were comparable to those produced by high‐performance liquid chromatography, suggesting practical applicability for trace‐level toxin analysis.

The enhanced sensing performance can be attributed to the synergistic properties of the BPQD–CNT architecture. The high surface area of BPQDs provides abundant adsorption sites for analyte interaction, while the conductive CNT backbone facilitates rapid electron transfer during electrochemical reactions. Additionally, the covalent attachment between the components improves structural integrity and prevents detachment or aggregation during repeated sensing cycles.

Nevertheless, several challenges should be considered when evaluating the broader applicability of this sensing strategy. The operational stability of BPQDs under ambient environmental conditions remains a concern due to their susceptibility to oxidation. Moreover, the detection range reported is suitable for laboratory‐scale testing but may require further optimization to meet stringent regulatory thresholds for food safety monitoring. Overall, the study demonstrates the potential of BPQD‐based nanohybrids as highly sensitive electrochemical sensing materials. However, future investigations should focus on improving environmental stability, extending detection ranges, and integrating such sensors into portable or real‐time monitoring systems suitable for field applications.

While the BPQD–CNT hybrid demonstrates excellent sensing performance, the origin of the enhancement remains insufficiently resolved. The reported improvement may arise from increased electroactive surface area, enhanced analyte adsorption, improved electron‐transfer kinetics, or a combination of these factors. However, current studies rarely deconvolute these contributions quantitatively. Consequently, the extent to which genuine electronic synergy exists between BPQDs and CNTs remains an open question. Future investigations should employ electrochemical impedance spectroscopy, surface‐area‐normalized analyses, and control architectures to clarify the mechanistic basis of performance enhancement.

4.3. BPQD‐Integrated Fluorescent Biosensors for Molecular Detection

Fluorescence‐based biosensing systems incorporating BPQDs have been developed to enable highly sensitive detection of biologically relevant molecules. A notable example involves the assembly of BPQDs within a metal–organic framework (MOF) matrix combined with silver nanoclusters to form multifunctional nanohybrids capable of ratiometric fluorescence detection [93]. In this architecture, the hybrid material exhibits dual emission peaks at 535 nm (blue) and 630 nm (red) under excitation at 440 nm, enabling internal calibration of the sensing signal.

The sensing mechanism relies on enzyme‐mediated catalytic reactions involving hydrogen peroxide and catalase. The presence of the target molecule accelerates the catalytic decomposition of H₂O₂, which in turn modulates the fluorescence response of the silver nanoclusters. While the red fluorescence intensity changes in response to the analyte, the emission originating from BPQDs remains relatively stable, providing a built‐in reference signal for ratiometric detection [93]. This dual‐signal strategy effectively reduces background interference and improves quantitative reliability.

Using this platform, detection of the target compound was achieved across a concentration range of 0.01–500 μg mL⁻¹, with a limit of detection of 3 ng mL⁻¹. The biosensor also demonstrated strong selectivity and stability when applied to practical samples. A particularly distinctive aspect of this system is its capability for visual detection, where fluorescence color changes can be directly observed with the naked eye. The platform was successfully applied to solution‐phase sensing, flexible substrates, and even latent fingerprint visualization.

Despite these promising features, the complexity of the nanohybrid architecture introduces several practical considerations. The fabrication process involves multiple components, including MOFs, metal nanoclusters, and enzymatic elements, which may complicate large‐scale reproducibility and increase fabrication costs. Furthermore, the long‐term operational stability of enzyme‐based systems can be limited due to enzymatic degradation under varying environmental conditions.

Nevertheless, the study highlights the versatility of BPQDs as functional components in advanced biosensing platforms. Their stable fluorescence characteristics and compatibility with hybrid nanostructures make them attractive candidates for next‐generation optical biosensors. Continued research aimed at simplifying device architectures and improving durability could further expand the applicability of BPQD‐based fluorescence sensing technologies.

Figure 3 demonstrates the working principle and analytical performance of the BPQD‐integrated ratiometric fluorescent biosensor described. Panels 3a and b show the fluorescence (FL) response of Ag nanoclusters (AgNCs) toward increasing H₂O₂ concentration. The gradual quenching of red emission at 630 nm results from oxidation of Ag⁰ to Ag⁺, and a strong linear relationship between relative fluorescence intensity and H₂O₂ concentration confirms sensitive detection capability. After incorporation into BPQDs‐doped MOF nanohybrids, panels 3c and d reveal a dual‐emission system: the red fluorescence (AgNCs, 630 nm) decreases with H₂O₂, whereas the blue fluorescence (BPQDs, 535 nm) remains nearly constant. The linear correlation between the ratiometric signal (I_{5 3 5}/I_{6 3 0}) and H₂O₂ concentration demonstrates the internal calibration advantage enabled by BPQDs.

FIGURE 3.

Fluorescence sensing performance of AgNCs and BPQD‐doped MOF nanohybrids. (a,b) H₂O₂‐induced quenching of AgNCs and corresponding linear response. (c,d) Ratiometric fluorescence behavior of nanohybrids toward H₂O₂. (e,f) Enzyme‐mediated ratiometric detection of BAI with linear correlation and high sensitivity, demonstrating BPQD‐enabled internal signal calibration. Adapted with permission from ref. [93]. 2020 Elsevier B.V.

Panels 3e and f illustrate the ratiometric detection of BAI through an enzyme‐mediated catalytic mechanism. In the presence of catalase and H₂O₂, increasing BAI concentration accelerates H₂O₂ decomposition, leading to the recovery of the fluorescence while the BPQD‐derived blue emission remains stable as a reference. This generates a concentration‐dependent variation in the I_{5 3 5}/I_{6 3 0} ratio with excellent linearity and a low detection limit (~3 ng mL⁻¹). These results highlight how BPQDs function as a stable internal fluorescence reference within the MOF‐based nanohybrid architecture, improving sensitivity, selectivity, and quantitative reliability in molecular detection.

Although the reported fluorescence biosensor exhibits excellent sensitivity and a remarkably low detection limit, it remains difficult to determine the specific contribution of BPQDs to the overall sensing performance. The sensing architecture incorporates multiple functional components, including MOFs, silver nanoclusters, and enzymatic elements, each of which may significantly influence signal amplification and selectivity. Consequently, the relative role of BPQDs as active sensing elements versus stable fluorescence references remains insufficiently quantified. Furthermore, the complexity of the multicomponent system may hinder reproducibility, scalability, and long‐term operational stability. Future studies should compare BPQD‐containing and BPQD‐free control systems under identical conditions to clarify the unique advantages provided by BPQDs and establish whether the observed performance gains justify the increased architectural complexity.

An important consideration for the future translation of BPQD‐based biosensors into practical biomedical and environmental applications is their biosafety profile. Although BPQDs are generally considered more biocompatible than many conventional heavy metal–based quantum dots because they ultimately degrade into phosphorus‐containing species, current evidence remains insufficient to establish their long‐term safety. Several studies have reported relatively low toxicity at moderate concentrations, whereas others have observed reactive oxygen species generation, oxidative stress, and concentration‐dependent reductions in cell viability. Furthermore, the biological effects of intermediate oxidation products formed during BPQD degradation remain poorly understood. Consequently, comprehensive investigations of cytotoxicity, immunogenicity, biodegradation pathways, and long‐term biological fate are required before BPQD‐enabled sensing platforms can be broadly implemented in clinical or environmental settings.

4.4. BPQD‐Enhanced Charge Extraction in Organic Solar Cells

BPQDs have also been incorporated into organic photovoltaic architectures to enhance charge extraction and reduce recombination losses. One approach utilized a heterostructured interlayer composed of BPQDs combined with PFN‐Br to improve the performance of non‐fullerene organic solar cells [94]. The introduction of BPQDs into the interfacial layer was shown to modify the electronic landscape at the electrode interface, enabling more efficient electron transport from the active layer toward the electrode.

The PFN‐Br/BPQD heterostructure contributed to several beneficial interfacial effects. First, the presence of BPQDs reduced the surface roughness of the interlayer, resulting in improved morphological compatibility with the adjacent layers. Second, the heterointerface created an additional built‐in electric field that facilitated electron extraction while suppressing charge recombination processes. These combined effects significantly improved device performance, leading to a power conversion efficiency (PCE) of 15.03%, with a maximum reported value of 15.20% [94]. This efficiency improvement highlights the potential of BPQDs as interfacial modifiers capable of tailoring the electronic properties of organic photovoltaic devices. Their nanoscale dimensions allow them to integrate within thin interlayers without disrupting the overall morphology of the device. Furthermore, their semiconducting characteristics enable favorable energy alignment between adjacent materials, which can facilitate more efficient carrier transport.

However, several aspects require further investigation before such strategies can be widely adopted. The stability of BPQDs within organic photovoltaic environments remains uncertain, particularly under prolonged illumination and exposure to oxygen or moisture. In addition, although the efficiency achieved is competitive, it represents an incremental improvement rather than a transformative breakthrough compared with other interfacial engineering approaches. Nevertheless, this study demonstrates that BPQDs can play a valuable role in optimizing interfacial charge dynamics in organic solar cells. Continued exploration of BPQD‐based heterostructures may lead to more sophisticated interface engineering strategies capable of further improving device efficiency and stability in next‐generation organic photovoltaic technologies.

The incorporation of BPQDs into interfacial layers clearly improves device efficiency; however, the magnitude of the enhancement remains relatively modest compared with the overall progress achieved in state‐of‐the‐art organic photovoltaic technologies. Although improved energy‐level alignment and reduced recombination are proposed as the primary mechanisms, the individual contributions of morphology optimization, interfacial dipole formation, and BPQD‐mediated charge extraction remain difficult to separate experimentally. Moreover, long‐term stability data under realistic operating conditions are still limited. Therefore, it remains unclear whether BPQDs provide a unique advantage over alternative interfacial modifiers or simply represent one of several viable interface‐engineering approaches. Comparative benchmarking against established interlayer materials is needed to assess their true technological significance.

Although the reported photovoltaic performance improvements demonstrate the effectiveness of BPQD‐based interface engineering, most studies rely on carefully optimized laboratory fabrication protocols, including solution processing under controlled environments. The influence of BPQD concentration, interlayer thickness, surface coverage, and solvent compatibility on device reproducibility and large‐area uniformity remains insufficiently understood. Furthermore, the scalability of these approaches beyond spin‐coated laboratory devices has yet to be demonstrated. Addressing these manufacturing‐related challenges will be essential for translating BPQD‐enabled photovoltaic technologies from proof‐of‐concept studies to commercially viable products.

4.5. BPQD‐Engineered Electron Transport Layers in Advanced Solar Cells

The integration of BPQDs into electron transport layers has emerged as another promising strategy for improving photovoltaic performance. In one study, BPQDs were introduced as additives into a SnO₂ nanoparticle precursor solution to engineer a modified electron transport layer for perovskite solar cells [95]. The resulting SnO₂/BPQD mixed layer significantly improved device efficiency and operational stability compared with conventional configurations.

The optimized device incorporating the mixed electron transport layer achieved a PCE of 21%, outperforming reference devices based on a pure SnO₂ layer (18.2%) and bilayer structures containing BPQDs and SnO₂ (19.5%–20.5%) [95]. This improvement was attributed to several synergistic effects. The presence of BPQDs reduced defect density within the SnO₂ layer, thereby suppressing trap‐assisted recombination. Additionally, strong interfacial interactions between BPQDs and SnO₂ enhanced charge transfer efficiency across the interface.

A notable advantage of the BPQD‐modified transport layer is its contribution to device stability. The system maintained more than 90% of its initial efficiency after 1000 h of illumination under AM 1.5 G conditions, while also exhibiting negligible hysteresis during current–voltage measurements [95]. These characteristics are particularly important for perovskite solar cells, where long‐term operational stability remains a major challenge.

Complementary investigations have also demonstrated that BPQDs can function as interlayers in organic solar cells, where their ambipolar charge transport and tunable bandgap facilitate cascade energy alignment between device layers. In such systems, the incorporation of BPQDs increased the efficiency of a PTB7‐Th:FOIC–based devices from 11.8% to 13.1%, while similar improvements were observed across multiple material systems, suggesting the general applicability of the approach [96].

Collectively, these results indicate that BPQDs can significantly influence interfacial charge transport processes in photovoltaic devices. Nevertheless, further research is required to understand long‐term material stability and to optimize integration strategies compatible with large‐scale manufacturing. Addressing these challenges will be crucial for translating BPQD‐based interfacial engineering from laboratory demonstrations to practical photovoltaic technologies.

Figure 4 presents a set of photophysical and electrochemical measurements demonstrating how incorporating BPQDs into the SnO₂ electron transport layer improves the performance of perovskite solar cells. Panel 4a shows that the PL intensity is significantly quenched in SnO₂/BPQD films, indicating effective defect passivation and enhanced electron extraction. Panel 4b displays TRPL decay curves, where the markedly shorter carrier lifetimes in the BPQD‐modified devices confirm faster charge transfer and reduced trap‐assisted recombination. Nyquist plots in panel 4c further reveal lower charge‐transfer resistance and improved interfacial transport in the mixed ETL. Finally, panel 4d shows the efficiency distribution of 30 devices, demonstrating higher average PCE and superior reproducibility when BPQDs are incorporated into the SnO₂ layer.

FIGURE 4.

(a) Steady‐state photoluminescence (PL) spectra of perovskite films deposited on pristine SnO₂ and SnO₂/BPQD electron transport layers, indicating enhanced charge extraction with BPQD incorporation. (b) Time‐resolved PL decay curves showing faster carrier dynamics in BPQD‐modified interfaces. (c) Nyquist plots from electrochemical impedance spectroscopy revealing reduced charge‐transfer resistance. (d) Statistical distribution of power conversion efficiencies for 30 devices, demonstrating improved performance and reproducibility in SnO₂/BPQD‐based perovskite solar cells. Adapted with permission from ref. [95]. 2024 American Chemical Society.

The efficiency increase from 18.2% to 21% and the improved operational stability demonstrate the potential of BPQD‐engineered electron transport layers. Nevertheless, the precise mechanisms responsible for performance enhancement remain only partially resolved. Defect passivation, conductivity improvement, interfacial energy‐level optimization, and suppression of charge recombination are all proposed to contribute simultaneously, making mechanistic deconvolution challenging. Furthermore, although stability exceeding 1000 h is encouraging, this duration remains substantially shorter than the requirements for commercial photovoltaic deployment. Additional studies employing operando spectroscopy and long‐term outdoor testing are required to determine the dominant stabilization mechanisms and evaluate whether BPQDs can provide durable performance advantages under practical operating environments.

Although the reported photovoltaic performance improvements demonstrate the effectiveness of BPQD‐based interface engineering, most studies rely on carefully optimized laboratory fabrication protocols, including solution processing under controlled environments. The influence of BPQD concentration, interlayer thickness, surface coverage, and solvent compatibility on device reproducibility and large‐area uniformity remains insufficiently understood. Furthermore, the scalability of these approaches beyond spin‐coated laboratory devices has yet to be demonstrated. Addressing these manufacturing‐related challenges will be essential for translating BPQD‐enabled photovoltaic technologies from proof‐of‐concept studies to commercially viable products.

Table 3 summarizes representative BPQD‐based hybrid architectures reported in recent literature for energy storage, electrochemical/fluorescent sensing, and solar cells. In LIB anodes, molecularly dispersed BPQDs on conductive 2D scaffolds significantly enhance capacity and cycling stability. In electrochemical and ratiometric fluorescent sensors, 0D/1D and MOF‐based hybrids improve sensitivity, selectivity, and visual readout capability. In organic and perovskite solar cells, BPQD‐engineered interlayers and ETLs optimize energy‐level alignment, charge extraction, hysteresis suppression, and long‐term operational stability.

TABLE 3.

Representative BPQD‐based hybrids in sensors and optoelectronic devices and their key performance metrics.

Ref. no.	Application/device type	BPQD configuration and hybrid structure	Key mechanism/functional role of BPQDs	Main performance metrics	Notable advantages/remarks
90	Lithium‐ion battery anode	BPQDs molecularly distributed on N‐doped graphene nanosheets (BPQDs/N‐graphene)	0D BPQDs provide abundant active sites and short Li+ diffusion paths; N‐graphene offers a conductive network and mechanical buffering, forming a van der Waals heterostructure	Reversible capacity ≈1271 mA h g−1 at 500 mA g−1; high cycling stability	Synergistic 0D/2D hybrid overcomes low conductivity and large volume expansion of BP; molecular‐level dispersion suppresses BPQD aggregation during cycling
91	Electrochemical sensor for ochratoxin A (OTA)	BPQDs anchored on carboxylated multiwalled CNTs (BPQDs/CNTs‐COOH, 0D/1D nanohybrid)	Covalent anchoring of BPQDs on CNTs‐COOH yields high conductivity, enlarged electroactive surface area, and pronounced antifouling behavior	Linear range: 0.4–10 μM; LOD: 0.03 μM; high reproducibility and anti‐interference capability	Robust OTA screening platform with performance comparable to HPLC; strong antifouling and stability in complex food matrices
92	Enzyme‐catalyzed ratiometric FL biosensor (baicalin detection)	Ag nanoclusters/BPQDs/MOF nanohybrids (dual‐emissive FL centers)	BPQDs doped in MOF serve as a stable blue FL reference; AgNCs provide a red FL response; enzyme‐mediated H2O2 decomposition modulates the FL ratio	Detection range: 0.01–500 μg mL−1; LOD: 3 ng mL−1; high sensitivity and selectivity	Enables solution, flexible substrate, and latent fingerprint visual detection; semiquantitative readout via naked‐eye observation of FL color change
93	Non‐fullerene organic solar cells (OSCs)	PFN‐Br/BPQDs interfacial heterostructure as electron‐extraction layer	BPQDs coordinate energy levels and create an additional built‐in field; reduced interface roughness and enhanced electron transport lower recombination losses	PCE: 15.03% (max 15.20%); improved Jsc and FF; reduced recombination	First rationally designed PFN‐Br/BPQDs interlayer for non‐fullerene OSCs; clearly demonstrates the interfacial engineering capability of BPQDs
94	Perovskite solar cells (PSCs), SnO2‐based ETL	BPQD‐engineered SnO2 ETL (SnO2/BPQDs mixed layer)	BPQDs passivate SnO2 defects, enhance conductivity, and suppress BPQD oxidation; improved charge extraction and negligible hysteresis	PCE: 21% (vs. 18.2% for pristine SnO2); > 90% efficiency retention after 1000 h under AM 1.5 G illumination; negligible hysteresis	Mixed SnO2/BPQDs ETL simultaneously boosts efficiency and long‐term stability; demonstrates mutual electronic and chemical stabilization
95	Organic solar cells with BPQD interlayers	BPQDs incorporated as interlayers at both ETL and HTL interfaces	BPQDs promote cascade band alignment and ambipolar charge transport, facilitating balanced electron/hole extraction	PCE enhanced from 11.8% to 13.1% (PTB7‐Th:FOIC); efficiency improvement also observed in other OSC systems	Versatile interlayer strategy applicable to both fullerene and non‐fullerene OSCs; highlights the universality of BPQD‐based interfacial modification

4.6. Multimodal Sensing and Energy–Optoelectronic Integration Enabled by BPQDs

An emerging trend in BPQD research is the development of multifunctional nanoplatforms that simultaneously integrate sensing, energy conversion, and optoelectronic functionalities within a single material system. Unlike earlier studies that focused on isolated device architectures, recent experimental works increasingly demonstrate that BPQDs can operate as versatile interfacial nanomaterials capable of bridging electrochemical sensing, optical detection, and photovoltaic energy systems. This multifunctionality arises from the combination of high surface reactivity, tunable electronic structure, and strong interfacial coupling with other nanomaterials.

Experimental evidence across multiple studies highlights the broad applicability of BPQD‐based hybrid architectures. In electrochemical environments, BPQDs integrated with conductive carbon frameworks such as nitrogen‐doped graphene nanosheets enable enhanced charge transport and ion storage, leading to high electrochemical capacities and improved reaction kinetics [91]. Similarly, BPQD‐based nanohybrids assembled with carbon nanotube networks demonstrate strong electron transfer capability and high surface adsorption activity, enabling sensitive electrochemical detection of toxic molecules in complex matrices [92]. These findings indicate that BPQDs can function as efficient catalytic and charge‐transfer centers in electrochemical sensing platforms.

In optical biosensing systems, the multifunctionality of BPQDs becomes even more evident. Hybrid architectures combining BPQDs with MOFs and metallic nanoclusters create ratiometric fluorescence platforms with improved signal reliability and reduced environmental interference [93]. In such systems, BPQDs provide stable emission characteristics that serve as internal optical references, enabling accurate fluorescence‐based detection across wide concentration ranges. The coexistence of catalytic, electronic, and optical functions within these nanohybrids illustrates the potential of BPQDs to act as central components in integrated sensing architectures.

The versatility of BPQDs is also reflected in optoelectronic energy devices. When incorporated into organic photovoltaic interlayers, BPQDs modify interfacial electronic properties and enhance charge extraction efficiency, leading to improved power conversion efficiencies in non‐fullerene solar cells [94]. Similar interfacial engineering strategies have been demonstrated in perovskite solar cells, where BPQD‐modified electron transport layers reduce defect density, suppress charge recombination, and improve long‐term device stability [95]. Moreover, BPQDs have been shown to facilitate cascade energy alignment in organic photovoltaic systems, enabling enhanced carrier transport across multiple material interfaces [96].

Collectively, these studies reveal a converging research direction in which BPQDs serve as multifunctional nanoscale bridges between sensing technologies and energy‐harvesting optoelectronic devices. This convergence is particularly attractive for next‐generation smart systems such as self‐powered sensors, wearable diagnostics, and integrated environmental monitoring platforms. However, realizing such multifunctional devices will require improved control over BPQD stability, interface engineering, and scalable fabrication methods. Continued investigation in these directions may enable BPQD‐based materials to play a central role in the development of highly integrated nanosystems that simultaneously perform sensing, energy conversion, and signal processing.

4.7. Comparative Assessment of BPQDs and Other Quantum Dot Systems

To fully evaluate the technological significance of BPQDs, it is important to compare their properties with those of other widely investigated zero‐dimensional nanomaterials, including graphene quantum dots (GQDs), carbon dots (CDs), and metal‐halide perovskite quantum dots (PQDs). Although all of these materials exhibit quantum confinement effects and size‐dependent optical properties, their performance characteristics, limitations, and application prospects differ substantially.

Among the major advantages of BPQDs is the presence of a tunable direct bandgap combined with relatively high carrier mobility. Unlike GQDs and CDs, which often exhibit indirect or defect‐dominated optical transitions, BPQDs possess intrinsically semiconducting electronic structures that facilitate efficient charge generation and transport. In addition, BPQDs inherit the anisotropic electronic characteristics of BP, providing unique opportunities for directional charge transport and polarization‐sensitive optoelectronic devices. Their strong light–matter interaction and phosphorus‐rich surface chemistry further enhance their suitability for sensing and interfacial engineering applications.

Compared with metal‐halide PQDs, BPQDs generally exhibit lower photoluminescence quantum yields but offer potentially lower environmental concerns because they do not contain toxic heavy metals such as lead. Furthermore, BPQDs can gradually degrade into phosphate‐containing products, which may improve their environmental compatibility relative to conventional semiconductor quantum dots. However, the biodegradation pathway and long‐term biosafety of BPQDs remain insufficiently understood [21, 22, 23, 24, 25].

Despite these advantages, BPQDs face significant challenges. Environmental instability remains their most critical limitation, as oxidation and hydrolysis can rapidly degrade their structure and performance under ambient conditions. In contrast, GQDs and CDs generally exhibit superior chemical stability and are easier to synthesize on a large scale. Similarly, PQDs often provide higher photoluminescence efficiencies and superior light‐emission performance, although they suffer from toxicity and stability concerns of their own.

From a practical perspective, BPQDs currently occupy a unique intermediate position among quantum‐dot materials. They combine favorable electronic transport properties with tunable optical behavior and rich surface chemistry, making them particularly attractive for sensing platforms, photodetectors, and interfacial engineering in photovoltaic devices. Nevertheless, challenges associated with stability, scalable manufacturing, and long‐term reliability must be overcome before BPQDs can compete broadly with more mature quantum‐dot technologies. Therefore, future research should focus not only on improving BPQD performance but also on clearly identifying application areas where their distinctive anisotropic electronic structure, direct bandgap, and phosphorus‐based surface chemistry provide advantages that cannot be readily achieved using established quantum‐dot systems.

To place BPQDs in the broader context of quantum‐dot research, Table 3 compares their key physicochemical and functional characteristics with those of other widely studied quantum‐dot systems, including GQDs, CDs, and metal‐halide PQDs. This comparison highlights both the unique advantages of BPQDs, such as their direct tunable bandgap, anisotropic charge transport, and rich phosphorus‐based surface chemistry, as well as their current limitations, particularly environmental instability and limited technological maturity.

As shown in Table 4, BPQDs occupy a distinctive position among quantum‐dot materials. Unlike GQDs and CDs, BPQDs combine a direct tunable bandgap with relatively high carrier mobility and strong light–matter interaction, making them particularly attractive for sensing and optoelectronic applications. However, their environmental instability remains a major challenge that currently limits practical deployment. In contrast, GQDs and CDs benefit from excellent chemical stability and scalable production, whereas perovskite QDs exhibit superior photoluminescence efficiencies but suffer from toxicity and long‐term stability concerns. These comparisons suggest that the future competitiveness of BPQDs will largely depend on advances in stability engineering and scalable synthesis while leveraging their unique electronic and interfacial properties in applications where conventional quantum dots offer limited performance advantages.

TABLE 4.

Comparative assessment of BPQDs and representative quantum‐dot materials for sensing and optoelectronic applications.

Property	BPQDs	GQDs	CDs	Metal‐Halide PQDs
Bandgap tunability	High; strongly size‐dependent direct bandgap	Moderate; largely defect and edge‐state dependent	Moderate; influenced by surface functional groups	Very high; composition and size tunable
Light–matter interaction	Strong excitonic effects and optical absorption	Moderate	Moderate	Very strong
Carrier mobility	Relatively high	Moderate	Low–moderate	Moderate
Charge‐transfer capability	Excellent for interfacial engineering and sensing	Good	Moderate	Good
Photoluminescence quantum yield (PLQY)	Moderate	Moderate	Moderate–high	Very high
Optical absorption range	Broad UV–NIR absorption	Mainly UV–visible	UV–visible	Visible–near IR
Surface chemistry	Rich phosphorus‐based reactive surface	Oxygen‐ and defect‐rich surface	Abundant functional groups	Surface‐ligand dependent
Environmental stability	Poor; susceptible to oxidation and hydrolysis	Excellent	Excellent	Moderate–poor
Toxicity concerns	Generally lower; degradation yields phosphate‐containing species	Low	Low	Potentially significant due to Pb‐containing compositions
Biodegradability	Potentially biodegradable	Limited	Limited–moderate	Limited
Scalability of synthesis	Currently limited	Well established	Highly scalable	Relatively mature
Device maturity	Emerging	Mature	Mature	Advanced
Unique advantages	Direct bandgap, anisotropic transport, high carrier mobility, phosphorus chemistry	Excellent stability and conductivity	Low cost, high biocompatibility	Exceptional optical emission and PLQY
Major limitations	Environmental instability and limited long‐term reliability	Lower carrier mobility and weaker optical absorption	Limited electronic performance	Toxicity and stability concerns

5. Challenges, Reliability, and Future Research Directions for BPQD‐Based Sensors and Optoelectronic Devices

5.1. Fundamental Stability and Degradation Pathways of BPQDs

Despite the exceptional physicochemical properties of BPQDs, environmental instability remains the most critical bottleneck preventing their widespread adoption in sensors and optoelectronic devices. BPQDs readily undergo photo‐oxidation and hydrolysis when exposed to oxygen, moisture, or light. Unlike bulk BP or few‐layer phosphorene, quantum dots possess a significantly larger surface‐to‐volume ratio, amplifying vulnerability to oxidation and causing accelerated structural decomposition. Upon degradation, P–P bonds break, oxidation states evolve toward PxOy species, and electronic structure deteriorates, leading to fluorescence quenching, reduced carrier mobility, and suppressed catalytic activity.

A key challenge lies in understanding the atomistic mechanisms of BPQD degradation. Most reported studies attribute instability to the formation of superoxide radicals on the BPQD surface, yet the exact interplay between defect density, edge chemistry, and environmental factors remains insufficiently resolved. Similarly, quantitative correlations between dot size, surface states, and degradation pathways are rarely established. As BPQD‐based devices move toward real‐world applications—particularly those requiring long‐term operation such as environmental toxin monitoring or photovoltaic power generation—predictive degradation models will be essential. Advanced characterization techniques (in situ TEM, X‐ray absorption spectroscopy, environmental AFM, and time‐resolved PL) can provide deeper insights, but comprehensive studies remain scarce.

Another fundamental barrier is the lack of standardized passivation strategies. Polymer encapsulation, heterostructure formation, and surface chemical modification have been explored, yet none fully eliminate long‐term degradation, especially under simultaneous illumination, bias, humidity, and temperature variations. For instance, while polymer coatings can slow oxidation, they often alter charge transport properties. Metal‐oxide shells improve stability but introduce mismatched band edges that hinder optoelectronic performance. The field therefore requires a unified passivation methodology that preserves intrinsic optical/electronic characteristics while ensuring durability. The stability challenge is not merely a materials issue; it directly dictates device reliability, accuracy, and lifetime. Addressing it requires both fundamental mechanistic studies and engineering‐level solutions capable of sustaining BPQD performance under realistic operational conditions.

A critical yet often overlooked aspect of BPQD stabilization is the trade‐off between environmental protection and preservation of intrinsic electronic properties. Polymer encapsulation, inorganic oxide coatings, and surface functionalization can substantially retard oxidation by limiting exposure to oxygen and moisture; however, these strategies may simultaneously influence charge transport, carrier mobility, and interfacial charge‐transfer dynamics. For example, thick polymer barriers can hinder carrier extraction, whereas metal‐oxide shells may introduce additional interfacial resistance or unfavorable band alignment. Consequently, stability enhancement should not be evaluated solely through increased lifetime but also through its impact on optoelectronic performance metrics. Future studies would benefit from standardized comparisons reporting degradation half‐life, environmental test conditions (humidity, illumination intensity, temperature), and corresponding changes in carrier mobility, photoluminescence efficiency, or device performance. Such quantitative benchmarking would enable a more rational assessment of stabilization approaches and accelerate the development of BPQD systems with both long‐term durability and high functionality.

5.2. Integration Challenges in Device Architectures and Large‐Scale Manufacturing

Although BPQDs have demonstrated substantial advantages in laboratory‐scale prototypes, scaling their synthesis and integration into complex device architectures remains a major challenge. Most current fabrication techniques, including liquid‐phase exfoliation, solvothermal synthesis, and bottom‐up growth, produce BPQDs with variability in size distribution, surface chemistry, and defect density. Even minor variations can translate into large shifts in optical absorption, charge transport behavior, or catalytic activity, leading to inconsistent device performance.

Large‐scale manufacturing faces three major barriers:

1. Reproducibility and Quality Control

   Industrial microfabrication requires batch‐to‐batch uniformity. However, BPQD synthesis is highly sensitive to solvent purity, reaction temperature, and oxidation during processing. Without precise control, variations in dot size or oxidation state reduce yield and compromise device reliability.

2. Compatibility with Device Processing Steps

   Many sensors and optoelectronic devices involve steps such as high‐temperature annealing, plasma cleaning, or chemical etching—conditions incompatible with BPQDs. Their surface reacts rapidly with aqueous processing environments and oxygen plasma, making integration with standard semiconductor processing difficult. Novel low‐temperature, inert‐environment protocols must be developed to enable BPQD incorporation into multilayer stacks without compromising functionality.

3. Interfacial Engineering and Structural Integrity

   BPQDs rarely operate as isolated entities; they must form interfaces with polymers, oxides, metals, and other nanomaterials. However, mismatches in work function, thermal expansion coefficients, and surface energy can lead to interfacial defects or delamination. In solar cells, for example, the long‐term stability of BPQD‐engineered interlayers depends critically on controlled chemical bonding at the BPQD/transport‐layer interface. Yet comprehensive studies evaluating interface durability under temperature cycling, humidity, or prolonged illumination are limited.

Another important challenge is the need for device‐level encapsulation. While encapsulation films can significantly enhance operational lifetime, their integration must avoid reducing optical transmission, altering refractive indices, or adding parasitic resistance. For flexible or wearable systems, encapsulation materials must also maintain mechanical compliance. To advance BPQDs toward commercialization, research must address issues of synthesis scalability, uniformity, process compatibility, and robust integration strategies that preserve both performance and structural integrity.

5.2.1. Processing Sensitivity and Manufacturing Constraints

Beyond material synthesis, the successful integration of BPQDs into functional device architectures presents several processing‐related challenges that remain insufficiently addressed in the current literature. Most high‐performance BPQD‐based optoelectronic devices have been fabricated using laboratory‐scale solution‐processing techniques, such as spin coating, which provide precise control over film formation but may not be directly compatible with industrial‐scale manufacturing. Furthermore, many reported fabrication procedures are conducted under inert atmospheres to minimize BPQD oxidation during deposition and post‐treatment, increasing process complexity and manufacturing cost.

An additional challenge arises from solvent compatibility. In multilayer photovoltaic architectures, BPQD dispersions must be deposited without damaging the underlying active layers. However, the solvent systems used to stabilize BPQDs may interact with organic semiconductors, perovskite absorbers, or transport layers, potentially inducing morphological changes, interfacial defects, or partial dissolution of previously deposited films. As a result, identifying orthogonal solvent systems that simultaneously preserve BPQD stability and device integrity remains a critical requirement for scalable device fabrication [89, 90, 91, 92].

Device performance is also highly sensitive to BPQD loading concentration, interlayer thickness, and surface coverage. Insufficient BPQD incorporation may provide only limited improvements in charge extraction, whereas excessive loading can promote aggregation, increase interfacial resistance, and introduce additional recombination pathways. Similarly, nonuniform surface coverage may lead to local variations in electronic properties and reduced device reproducibility. Despite the importance of these parameters, systematic studies establishing processing–structure–performance relationships remain relatively scarce.

These challenges are particularly relevant for BPQD‐based solar cells, where the highest efficiencies have generally been achieved under carefully optimized laboratory conditions. The transition from spin‐coated prototype devices to scalable manufacturing approaches, such as slot‐die coating, blade coating, inkjet printing, or roll‐to‐roll processing, remains largely unexplored. Consequently, future research should focus not only on improving device efficiency but also on developing robust, oxidation‐resistant, and manufacturing‐compatible BPQD processing strategies suitable for large‐area and high‐throughput production.

5.3. Assessing Reliability, Operational Lifetime, and Environmental Robustness

The transition of BPQD‐based technologies from laboratory research to practical devices depends heavily on reliability metrics, lifetime assessment, and environmental robustness. However, unlike mature semiconductor technologies, BPQD‐based systems lack standardized testing frameworks. Most studies evaluate performance under controlled laboratory conditions, overlooking dynamic real‐world environments.

Operational lifetime remains a key concern. In sensors, degradation of BPQDs leads to reduced sensitivity, background signal drift, and loss of repeatability. In photovoltaic devices, photo‐oxidation reduces open‐circuit voltage, increases recombination centers, and deteriorates interfacial charge transfer. Only a few studies—particularly in BPQD‐modified perovskite solar cells—have reported stability tests over hundreds of hours, and even these conditions rarely reflect outdoor temperature fluctuations, UV exposure, or long‐term humidity stress.

Mechanical reliability is another emerging issue as BPQDs are increasingly incorporated into flexible, wearable, or stretchable systems. Mechanical deformation can alter BPQD spatial distribution, disrupt chemical bonding at interfaces, and accelerate surface oxidation by generating local strain. The absence of comprehensive mechanical fatigue studies leaves a knowledge gap preventing deployment in flexible electronics or bio‐integrated devices.

Beyond device‐level stability, environmental and biological compatibility requires further investigation. BPQDs degrade into phosphate species that are generally considered nontoxic, yet the intermediate oxidation products, their long‐term cytocompatibility, and environmental accumulation pathways are not well understood. As BPQDs are increasingly explored for biosensing and medical diagnostics, rigorous cytotoxicity, hemocompatibility, and biodegradation studies will be essential.

Finally, a major reliability challenge is the lack of accelerated aging models tailored to BPQDs. Standard semiconductor aging tests cannot be directly applied due to the unique degradation chemistry of phosphorene derivatives. Developing protocols that correlate accelerated stress results with long‐term real‐world behavior will be crucial for industrial adoption.

5.3.1. Toward Standardized Characterization and Reporting Protocols for BPQDs

A major obstacle hindering the maturation of BPQD research is the absence of standardized characterization and reporting protocols. Although numerous studies report promising sensing and optoelectronic performances, direct comparison between published results remains challenging because material characterization, device testing conditions, and stability assessment procedures vary considerably across research groups. Consequently, establishing community‐wide standards would significantly improve reproducibility, benchmarking, and technology translation.

At the material level, a minimum characterization framework should be adopted for all newly synthesized BPQDs. Structural characterization should include X‐ray diffraction (XRD) and Raman spectroscopy to confirm phase purity and evaluate oxidation‐induced structural changes. Importantly, these measurements should ideally be performed both before and after device operation or stability testing to assess degradation pathways. In addition, TEM should be accompanied by statistical analyses of particle size and thickness distributions rather than representative images alone, thereby providing a more accurate description of sample heterogeneity [85, 86, 87, 88].

Optical and electronic characterization should also be standardized. UV–Vis absorption spectroscopy, photoluminescence spectroscopy, and consistent bandgap determination methods should be reported to facilitate meaningful comparisons between studies. Furthermore, information regarding defect density, surface chemistry, oxidation state, and surface functionalization should be systematically documented because these factors strongly influence BPQD performance.

At the device level, performance metrics should be accompanied by standardized stability assessments. Environmental stress testing under controlled humidity, temperature, illumination intensity, and atmospheric conditions should be routinely reported. For photovoltaic applications, protocols analogous to the International Summit on Organic and Organic–Inorganic Photovoltaic Stability (ISOS) standards could provide a useful framework for evaluating operational stability and facilitating cross‐study comparisons. Similar standardized protocols should be developed for sensing devices, including long‐term signal stability, repeatability, selectivity retention, and environmental robustness.

Finally, future publications should report sufficient experimental details regarding synthesis conditions, storage environments, device fabrication procedures, and testing protocols to enable independent reproducibility. The establishment of standardized characterization and reporting practices would not only improve the reliability of published data but also accelerate the transition of BPQD technologies from exploratory laboratory studies toward engineering‐oriented development and commercial implementation.

5.4. Future Research Opportunities and Strategic Directions

Looking ahead, the field of BPQD‐based devices is poised for significant expansion, provided that emerging challenges are addressed through targeted research. Several key directions stand out:

1. Advanced Passivation and Core–Shell Architectures

   Stabilization strategies must evolve beyond simple polymer or oxide coatings. Novel approaches such as atomic layer–deposited ultrathin shells, 2D heterostructure encapsulation, and covalent ligand engineering offer promising methods to preserve BPQD properties while enabling device integration.

2. Standardized, Scalable Synthesis with Precise Size Control

   Future work should focus on producing BPQDs with uniform electronic and optical characteristics through automated microreactor systems, continuous‐flow synthesis, or surfactant‐assisted growth. Integration of in situ spectroscopy into synthesis workflows could enable real‐time quality monitoring.

3. Interfacial Engineering for High–Efficiency Devices

   Tailoring BPQD energy levels to optimize charge transfer will be crucial for next–generation solar cells, photodetectors, and light–emitting devices. This includes designing tailored molecular linkers, functional ligands, and multilayered junctions that minimize recombination losses.

4. Self–Powered and Multifunctional Device Platforms

   BPQDs possess unique characteristics enabling synergistic integration of sensing and energy systems—an emerging trend in intelligent diagnostics and IoT devices. Future research may explore:

   • self‐powered toxin sensors using photovoltaic BPQD interfaces
   • dual‐mode (optical + electrochemical) biosensors
   • hybrid nanoarchitectures coupling BPQD photodetection with energy harvesting

   Such multifunctional platforms could significantly enhance device autonomy and broaden real‐world applicability.

5. Machine Learning–Assisted Materials Design

   Leveraging machine learning to predict BPQD stability, optimize synthesis parameters, or design interfacial layers could accelerate the discovery of high‐performance device architectures. Data‐driven approaches are especially valuable given the multidimensional parameter space involving BPQD size, surface state, oxidation level, and environmental factors.

6. Comprehensive Reliability Frameworks

   The community must develop standardized protocols for evaluating BPQD oxidation kinetics, mechanical fatigue, and photo‐stability. This will require coordinated efforts combining theoretical modeling, in situ monitoring, and long‐term aging tests.

In conclusion, while BPQDs offer remarkable opportunities for next‐generation sensors and optoelectronic devices, their practical implementation requires major advances in stability engineering, scalable synthesis, interfacial design, and reliability assessment. Through strategic and interdisciplinary research, BPQDs have the potential to evolve into foundational materials for integrated, high‐performance nanosystems.

Beyond BPQDs, recent advances in related 2D materials provide valuable insights for future BPQD research. Antimonene‐based surface plasmon resonance sensors have demonstrated ultrasensitive biomolecular detection down to the attomolar level, highlighting the importance of strong analyte–surface interactions in next‐generation sensing platforms [97]. Similarly, anisotropic optoelectronic responses reported in β‐InSe photodetectors emphasize the potential of exploiting directional charge transport and polarization sensitivity in low‐dimensional materials [98]. Progress in the epitaxial growth of large‐area, highly crystalline BP films on silicon substrates further illustrates possible pathways toward scalable manufacturing and device integration [99]. In addition, studies on anisotropic water adsorption and liquefaction on BP surfaces reveal the critical role of surface chemistry and crystallographic orientation in environmental stability and interfacial processes [100]. Collectively, these developments suggest promising directions for advancing BPQD synthesis, device engineering, stability control, and application‐specific optimization.

5.5. Toxicity, Biosafety, and Environmental Fate of BPQDs

Although BPQDs have attracted significant attention for biosensing, biomedical, and environmental applications, their toxicity and environmental fate remain insufficiently understood. This issue is particularly important because BPQDs are intentionally designed to interact with biological systems and, in many applications, may eventually be released into environmental matrices. Consequently, evaluating their degradation products, biological responses, and long‐term environmental behavior is essential for assessing their practical safety.

The degradation of BPQDs generally proceeds through oxidation and hydrolysis processes, leading to the formation of phosphorus oxides (PxOy), phosphite species, and ultimately phosphate ions. Because phosphate is a naturally occurring and biologically relevant nutrient, BPQDs are often considered more environmentally benign than many heavy metal–based quantum dots. However, the transformation pathway from pristine BPQDs to final phosphate products may involve reactive intermediate species capable of generating oxidative stress in biological systems.

Current toxicological studies present mixed conclusions. Several reports suggest that BPQDs exhibit relatively good biocompatibility at low concentrations and can be gradually biodegraded into phosphate‐containing products. In contrast, other investigations have demonstrated that elevated BPQD concentrations may induce reactive oxygen species (ROS) generation, mitochondrial dysfunction, membrane damage, and reduced cell viability. These observations indicate that cytotoxicity is highly dependent on particle size, surface chemistry, dosage, exposure duration, and degradation state [34, 35, 36, 37, 38, 39].

Beyond cellular toxicity, the immunological and environmental consequences of BPQD exposure remain poorly understood. Limited information is available regarding inflammatory responses, long‐term biodistribution, bioaccumulation, and ecological impacts in aquatic or terrestrial systems. Furthermore, the environmental persistence of partially oxidized BPQD intermediates has not been systematically investigated. As a result, the assumption that BPQDs are inherently safe solely because they eventually degrade into phosphate species may be overly simplistic.

Future studies should therefore combine mechanistic toxicology, biodegradation analysis, and environmental risk assessment to establish comprehensive biosafety frameworks. Standardized protocols evaluating cytotoxicity, oxidative stress, immunogenicity, biodegradation kinetics, and environmental persistence will be essential before BPQD‐based technologies can be widely deployed in biomedical diagnostics, biosensing platforms, and environmental monitoring systems.

5.6. Structure–Property–Application Relationships in BPQDs

A central challenge in BPQD research is establishing clear relationships between synthesis conditions, resulting structural characteristics, functional properties, and ultimate device performance. Although numerous studies have reported improved sensing and optoelectronic behavior, the underlying structure–property–application correlations are often discussed separately rather than within a unified framework. As a result, the rational design of BPQDs for specific applications remains difficult.

The physicochemical properties of BPQDs are strongly influenced by synthesis parameters, including precursor chemistry, reaction temperature, reaction time, solvent environment, and post‐synthesis surface treatments. Variations in these parameters directly affect particle size, crystallinity, defect density, edge termination, oxidation state, and surface chemistry. These structural characteristics subsequently determine key electronic and optical properties such as bandgap energy, charge‐carrier mobility, trap‐state density, photoluminescence behavior, charge‐transfer efficiency, and environmental stability.

For example, reducing BPQD size generally strengthens quantum confinement effects, resulting in wider bandgaps and tunable photoluminescence, which are advantageous for fluorescence‐based sensing applications. Conversely, increased defect density may create additional active sites that enhance catalytic and electrochemical activity but simultaneously introduce trap states that reduce charge‐transport efficiency. Similarly, improved crystallinity often suppresses carrier recombination and enhances electronic transport, making highly ordered BPQDs more suitable for photovoltaic and photodetector applications.

Surface engineering provides another important design variable. Functionalization and passivation strategies can improve environmental stability and analyte binding capability, thereby enhancing biosensing performance [49, 50, 51, 52, 53]. However, excessive surface modification may alter intrinsic electronic properties and impede charge transport. Consequently, optimization frequently requires balancing stability, electronic performance, and application‐specific requirements.

Despite significant progress, many structure–property relationships remain incompletely understood. In particular, quantitative correlations between defect chemistry, edge structure, oxidation state, and device‐level performance are still lacking. Future studies combining advanced characterization techniques with systematic device benchmarking will be essential for establishing predictive design rules and accelerating the development of application‐specific BPQD technologies.

To provide a unified perspective on BPQD design principles, Table 5 summarizes the major relationships between synthesis parameters, resulting structural features, corresponding electronic and optical properties, and the applications that benefit most from these characteristics. This framework highlights how modifications introduced during synthesis ultimately govern device performance and identifies areas where mechanistic understanding remains limited.

TABLE 5.

Structure–property–application relationships in BPQDs: linking synthesis parameters, structural characteristics, functional properties, and target applications.

Synthesis parameter/processing factor	Structural consequence	Resulting property change	Most relevant applications	Current knowledge gap
Higher solvothermal reaction temperature	Improved crystallinity and reduced structural disorder	Lower trap‐state density, improved carrier transport	Solar cells, photodetectors	Quantitative correlation between crystallinity and device efficiency remains limited
Smaller BPQD size	Stronger quantum confinement	Larger bandgap, blue‐shifted photoluminescence, size‐tunable optical response	Fluorescence biosensors, optical probes	Size‐dependent excitonic behavior not fully understood
Longer reaction time	Growth of larger domains and modified edge structure	Reduced confinement effect, altered absorption/emission spectra	Optoelectronics, photonics	Precise growth mechanisms remain unclear
Increased defect density	More edge sites and localized states	Enhanced catalytic activity but increased carrier trapping	Electrochemical sensing, catalysis	Defect‐type–specific effects remain poorly quantified
Surface oxidation	Formation of phosphorus oxide species	Reduced carrier mobility and photoluminescence efficiency	Generally detrimental to most devices	Oxidation kinetics and degradation pathways remain incompletely resolved
Surface functionalization	Modified surface chemistry and binding sites	Improved stability, dispersibility, and analyte affinity	Biosensors, environmental monitoring	Trade‐off between stability and electronic performance
Polymer or inorganic passivation	Reduced exposure to oxygen and moisture	Enhanced environmental stability and operational lifetime	Practical sensing and optoelectronic devices	Long‐term interfacial effects remain unclear
Formation of BPQD/carbon heterostructures	Improved interfacial contact and charge‐transfer pathways	Enhanced conductivity and electrochemical activity	Batteries, electrochemical sensors	Relative contributions of surface area and electronic synergy remain debated
BPQD incorporation into transport layers	Optimized interfaces and reduced defect density	Faster charge extraction and lower recombination losses	Organic and perovskite solar cells	Sensitivity to thickness, loading concentration, and coverage requires further study

As summarized in Table 5, BPQD performance is ultimately governed by a cascade of interconnected relationships linking synthesis conditions to structural characteristics, functional properties, and application outcomes. While several qualitative trends have been established, many causal relationships remain only partially understood, particularly those involving defect chemistry, edge termination, oxidation state, and interfacial charge‐transfer processes. Developing quantitative structure–property–performance models therefore represents an important future research direction and will be essential for the rational design of BPQDs tailored to specific sensing and optoelectronic applications.

5.7. Performance Variability and Literature Bias in BPQD Research

While numerous studies have demonstrated promising improvements in the performance of BPQD‐based sensors and optoelectronic devices, the current literature may not fully reflect the variability that exists across different experimental systems. Most highly cited reports emphasize successful implementations and record‐level performances, whereas studies reporting marginal improvements, limited benefits, or unsuccessful device integration are comparatively less visible. Consequently, the overall effectiveness of BPQDs may occasionally appear more universally applicable than is actually supported by the available evidence.

In photovoltaic applications, for example, the incorporation of BPQDs generally leads to improved charge extraction, reduced recombination losses, and enhanced PCE. However, the magnitude of these improvements varies considerably depending on device architecture, interfacial engineering, BPQD concentration, and processing conditions. In some studies, only modest efficiency gains have been observed, suggesting that BPQDs should be regarded as performance‐enhancing components rather than universally transformative materials [78, 79, 80, 81, 82, 83].

A similar situation exists in sensing applications, where reported improvements in sensitivity and detection limits are often strongly dependent on surface chemistry, hybrid‐material design, and analyte‐specific interactions. Furthermore, because many sensing platforms incorporate multiple functional nanomaterials simultaneously, isolating the precise contribution of BPQDs to the overall performance remains challenging.

These observations highlight the need for more systematic benchmarking studies, standardized testing protocols, and reproducibility assessments across independent research groups. Future progress in the field will depend not only on achieving higher performance metrics but also on establishing the reliability, consistency, and generalizability of BPQD‐enabled device improvements under realistic operating conditions.

6. Conclusion

BPQDs have rapidly emerged as promising nanomaterials for next‐generation sensing and optoelectronic technologies due to their tunable band structure, strong light–matter interaction, high carrier mobility, and versatile surface chemistry. This review has systematically discussed the fundamental properties of BPQDs, their synthesis strategies, and their integration into a variety of functional devices. Particular emphasis was placed on their roles in electrochemical and optical sensors, as well as their implementation in optoelectronic systems such as organic and perovskite solar cells. These studies collectively demonstrate that BPQDs can significantly enhance charge transport, interfacial energy alignment, and signal amplification, leading to improved device sensitivity and efficiency.

Despite these promising advances, several challenges continue to limit the large‐scale adoption of BPQD‐based technologies. Environmental instability, difficulties in scalable synthesis with precise structural control, and the lack of standardized reliability assessments remain key barriers to commercialization. Addressing these issues will require coordinated progress in materials stabilization, interface engineering, and device fabrication methodologies.

Future research is expected to move toward multifunctional platforms where BPQDs simultaneously enable sensing, energy conversion, and signal processing within integrated nanosystems. With continued advances in stability engineering, scalable production, and intelligent device design, BPQDs are poised to play an important role in the development of high‐performance, miniaturized, and energy‐efficient technologies for environmental monitoring, healthcare diagnostics, and advanced optoelectronic applications.

Author Contributions

Mohamed Abu Shuheil: conceptualization, investigation, writing – original draft. Chirag G. Makvana: investigation, methodology, writing – original draft. Masharipov Kamolbek Ko'palovich: methodology, data curation, writing – original draft. Hussein Khaled Nwr: resources, software, writing – review and editing. Rasha Ali Abdalhuseen: investigation, writing – review and editing. Monika Verma: writing – review and editing, formal analysis, supervision. Divya Singhal: writing – review and editing, visualization, formal analysis. Ahmad Esmaeilpour: conceptualization, writing – review and editing, project administration, supervision.

Funding

The authors have nothing to report.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

Data sharing not applicable. No new data generated.