Recent Advances in Antimony Sulfide (Sb2S3) Thin Films

Bhushan B. Chaudhari^1,3, Navnath M. Yajgar¹, Bharat G. Thakare¹, Niranjan S. Samudre¹, Rajendra R. Ahire¹,Amol R Naikda^1,2, Dhananjay S Patil⁴_,Nanasaheb P. Huse³, Sudam D. Chavhan^1*

¹Department of Physics, Vidya Vikas Mandal’s Sitaram Govind Patil ASC College, Sakri, Dhule, Maharashtra, India

²Department of Physics S.S.V.P. S’s L.K.Dr. P.R.Ghogrey Science College Dhule, Maharashtra, India

³Department of Physics, Nandurbar Taluka Vidhayak Samiti’s G. T. Patil Arts, Commerce and Science College, Nandurbar, Maharashtra, India

⁴Department of Zoology, Nandurbar Taluka Vidhayak Samiti’s G. T. Patil Arts, Commerce and Science College, Nandurbar, Maharashtra, India

*Corresponding Author: sudam1578@gmail.com

Abstract

Antimony sulfide (Sb2S3) has emerged as a promising earth-abundant and environmentally benign semiconductor for next-generation thin-film photovoltaic and optoelectronic applications [1].The material exhibits a suitable bandgap, high optical absorption coefficient, and excellent chemical stability, making it a strong candidate for low-cost solar energy conversion technologies [2].Unlike conventional chalcogenide absorbers such as CdTe and CIGS, Sb2S3 does not rely on toxic or scarce elements, which significantly improves its sustainability profile [3].Sb2S3 crystallizes in an orthorhombic structure composed of quasi-one-dimensional (Sb2S3) ribbon chains, resulting in highly anisotropic electrical and optical properties [4].These anisotropic characteristics strongly influence charge transport, defect formation, and device performance in thin-film solar cells [5].In recent years, extensive research efforts have been dedicated to controlling the morphology, crystallinity, and orientation of Sb2S3 thin films to overcome efficiency limitations [6].Various deposition techniques, including chemical bath deposition, spin coating, atomic layer deposition, spray pyrolysis, and thermal evaporation, have been systematically explored to optimize film quality [7].Furthermore, interface engineering, defect passivation, elemental doping, and post-treatment strategies have enabled significant improvements in power conversion efficiency [8].This review critically summarizes the fundamental structural and optoelectronic properties of Sb2S3 and correlates them with thin-film growth mechanisms and device performance [9].Special emphasis is placed on recent advances in Sb2S3-based solar cell architectures and performance optimization strategies [10].Finally, the remaining challenges and future research directions required for the commercialization of Sb2S3 thin-film technologies are discussed [11].

Keywords:Sb2S3 thin films; chalcogenide semiconductors; photovoltaic materials; solar cells.

1. Introduction

The continuous growth of global energy demand, coupled with the environmental impact of fossil fuel consumption, has intensified the search for sustainable and renewable energy technologies [12].Among various renewable energy sources, solar energy is considered the most abundant and universally accessible, with the potential to meet global energy requirements if efficiently harvested [13].Photovoltaic (PV) technologies play a central role in converting solar radiation directly into electrical energy, driving extensive research on advanced semiconductor materials [14].Conventional thin-film solar cell technologies, such as cadmium telluride (CdTe) and copper indium gallium selenide (CIGS), have demonstrated high power conversion efficiencies exceeding 22% [15].However, the large-scale deployment of these technologies is constrained by toxicity concerns, elemental scarcity, and high fabrication costs [16].As a result, earth-abundant and environmentally friendly absorber materials have attracted significant scientific and technological interest [17].Antimony sulfide (Sb2S3) is a binary chalcogenide semiconductor belonging to the A₂B₃ family (A = Sb, Bi; B = S, Se) and has emerged as a promising alternative absorber material [18].Sb2S3 exhibits a direct bandgap in the range of 1.6–1.8 eV, which is well suited for efficient absorption of visible solar radiation [19].The material also possesses a high absorption coefficient on the order of 10⁴–10⁵ cm⁻¹, enabling effective light harvesting with ultrathin absorber layers [20].

In addition to its favorable optical properties, Sb2S3 demonstrates good chemical stability under ambient conditions and resistance to moisture-induced degradation [21].These features make Sb2S3 particularly attractive for low-cost and scalable photovoltaic applications [22].Structurally, Sb2S3 crystallizes in an orthorhombic phase composed of one-dimensional ribbon-like (Sb2S3)ₙ chains extending along the crystallographic c-axis [23].The strong covalent bonding within these ribbons and weak van der Waals interactions between adjacent chains lead to pronounced anisotropy in charge transport properties [24].Such anisotropic behavior significantly influences carrier mobility, recombination dynamics, and defect formation in Sb2S3 thin films [25].Consequently, the orientation and morphology of Sb2S3 crystals play a crucial role in determining device performance [26].Understanding the relationship between crystal structure, thin-film growth, and photovoltaic behavior is therefore essential for the rational design of high-efficiency Sb2S3 solar cells [27].Sb2S3-based solar cells typically adopt device architectures similar to semiconductor-sensitized or planar heterojunction solar cells [28].These architectures commonly consist of a transparent conducting oxide, an electron transport layer, the Sb2S3 absorber, a hole transport material, and a metallic back contact [29].Despite a theoretically predicted efficiency exceeding 25%, experimentally reported efficiencies of Sb2S3 solar cells remain below 8% [30].The discrepancy between theoretical and experimental performance is primarily attributed to defect-induced recombination, poor carrier extraction, and sub-optimal interfaces [31].

Recent research has therefore focused on improving film quality, reducing trap density, and optimizing interfacial energetics [32].This review provides a comprehensive and critical analysis of Sb2S3 thin-film materials, emphasizing structure–property–performance relationships [33].The discussion begins with fundamental structural and optoelectronic properties of Sb2S3, followed by an overview of major thin-film deposition techniques [34].

Recent progress in device engineering, defect passivation, and performance enhancement strategies is systematically examined [35].By consolidating current knowledge and identifying key challenges, this review aims to guide future research toward highly efficient and commercially viable Sb2S3-based photovoltaic technologies [36].

(Schematic illustration of the quasi-one-dimensional crystal structure of Sb2S3 showing (a) the side view and top perspective of the orthorhombic lattice, and (b) the arrangement of [Sb₄S₆] ribbon units extending along the crystallographic c-axis, highlighting strong intra-ribbon bonding and weak inter-ribbon interactions that govern anisotropic physical properties [8, 23, 244].)

2. Crystal Structure and Fundamental Properties of Sb2S3

2.1 Crystal Structure of Antimony Sulfide (Sb2S3)

Antimony sulfide (Sb2S3) crystallizes in a thermodynamically stable orthorhombic phase with the space group Pnma under ambient conditions [37].The crystal lattice is characterized by lattice parameters a ≈ 11.3 Å, b ≈ 3.8 Å, and c ≈ 11.2 Å, indicating a highly anisotropic unit cell geometry [38].The fundamental structural motif of Sb2S3 consists of quasi-one-dimensional (Sb₄S₆)ₙ ribbon-like chains that extend parallel to the crystallographic c-axis [39].Within each ribbon, antimony atoms are coordinated with sulfur atoms through strong covalent bonds, forming a robust backbone for charge transport [40].Adjacent ribbons are held together by weak van der Waals interactions, resulting in easy cleavage along planes perpendicular to the b-axis [41].

The anisotropic bonding nature leads to directional dependence of mechanical, electrical, and optical properties in Sb2S3 crystals [42].Charge carriers preferentially transport along the ribbon direction due to reduced effective mass and stronger orbital overlap [43].In contrast, carrier transport perpendicular to the ribbon direction is hindered by weak inter-chain interactions, leading to reduced conductivity [44].This intrinsic anisotropy plays a decisive role in determining thin-film orientation and device efficiency [45].Experimental studies have demonstrated that Sb2S3 thin films with preferential orientation along the (hk0) planes exhibit improved photovoltaic performance [46].Such orientation facilitates efficient charge transport from the absorber to the charge-selective contacts [47].Therefore, controlling thecrystallographic orientation during film growth is a critical requirement for high-efficiency Sb2S3-based devices [48].

Orthorhombic crystal structure of Sb2S3 illustrating one-dimensional (Sb₄S₆)ₙ ribbon chains along the c-axis and weak inter-chain interactions. [8, 23, 244]

2.2 Electronic Band Structure and Anisotropy

Sb2S3 is a semiconductor with a bandgap that lies in the optimal range for single-junction solar cell applications [49].At room temperature, crystalline Sb2S3 exhibits a direct bandgap with reported values ranging from 1.6 to 1.8 eV depending on film quality and crystallinity [50].Amorphous Sb2S3 films, in contrast, often exhibit an indirect bandgap due to structural disorder and localized defect states [51].The conduction band minimum is primarily composed of Sb 5p orbitals, while the valence band maximum arises mainly from hybridized Sb 5s and S 3p orbitals [52].Density functional theory calculations reveal strong dispersion of electronic bands along the ribbon direction and relatively flat bands perpendicular to it [53].This anisotropic band dispersion results in direction-dependent effective masses for electrons and holes [54].Lower effective mass along the ribbon axis enables higher carrier mobility, which is beneficial for charge extraction in thin-film devices [55].However, misaligned crystal orientation in polycrystalline films can severely limit carrier transport and increase recombination losses [56].The electronic anisotropy of Sb2S3 also affects defect formation energies and trap-state distributions [57].Sulfur vacancies and antimony antisite defects introduce deep-level trap states within the bandgap [58].These trap states act as recombination centers, reducing carrier lifetime and open-circuit voltage in photovoltaic devices [59].Consequently, defect control and passivation strategies are essential for achieving high-performance Sb2S3 solar cells [60].

Conceptual energy band diagram of Sb2S3 illustrating direction-dependent electronic dispersion, with enhanced band curvature along the quasi-one-dimensional ribbon (c-axis) direction and comparatively reduced dispersion perpendicular to the ribbon chains, reflecting anisotropic charge transport behavior [23, 245, 246].

2.3 Optical Properties

Sb2S3 exhibits a high optical absorption coefficient exceeding 10⁵ cm⁻¹ in the visible region, enabling strong light absorption within thicknesses below 500 nm [61].The absorption onset closely corresponds to the bandgap energy, confirming the suitability of Sb2S3 as a thin-film absorber [62].Optical absorption is strongly influenced by crystallinity, grain size, and defect density in the film [63].Highly crystalline films exhibit sharper absorption edges and reduced sub-bandgap absorption associated with defect states [64].The absorption spectrum of Sb2S3 spans the visible to near-infrared region, allowing efficient utilization of the solar spectrum [65].Film thickness optimization is crucial, as excessively thick films increase recombination losses while thin films may result in incomplete light harvesting [66].Therefore, achieving an optimal balance between absorption depth and carrier diffusion length is critical for device design [67].

Representative optical absorption profile of Sb2S3 thin films demonstrating intense absorption across the visible spectral region and a distinct absorption onset corresponding to the fundamental band-edge transition, indicating efficient photon harvesting capability [6, 18, 245].

2.4 Electrical and Charge Transport Properties

Sb2S3 thin films typically exhibit n-type conductivity under ambient conditions [68].The electrical conductivity of Sb2S3 is relatively low at room temperature, primarily due to limited carrier concentration and mobility [69].Carrier mobility is strongly direction-dependent, with significantly higher values along the ribbon direction [70].Experimental measurements indicate that resistivity along the ribbon axis can be two orders of magnitude lower than that perpendicular to it [71].Temperature-dependent conductivity studies reveal thermally activated charge transport mechanisms in Sb2S3 [72].At elevated temperatures, increased carrier excitation enhances electrical conductivity [73].Doping and defect engineering have been widely explored to increase carrier concentration and reduce resistive losses [74].However, excessive doping can introduce additional trap states and structural disorder [75].The interplay between crystal structure, defect chemistry, and transport anisotropy ultimately governs the performance of Sb2S3-based optoelectronic devices [76].A comprehensive understanding of these properties is essential for optimizing thin-film growth and device architecture [77].

Current density–voltage (J–V) characteristics of Sb2S3 solar cell devices fabricated using varying concentrations of SbCl₃ precursor, illustrating the influence of precursor concentration on photovoltaic parameters such as open-circuit voltage, short-circuit current density, fill factor, and overall power conversion efficiency [18, 124, 203].

3. Thin-Film Deposition Techniques for Sb2S3

3.1 Importance of Deposition Technique Selection

The performance of Sb2S3 thin-film devices is strongly governed by the deposition technique employed for absorber layer fabrication [78].Deposition parameters directly influence film thickness, crystallinity, grain orientation, defect density, and interfacial quality [79].Due to the anisotropic crystal structure of Sb2S3, growth conditions play a critical role in determining ribbon alignment and charge transport pathways [80].Consequently, a wide range of physical and chemical deposition techniques have been explored to achieve high-quality Sb2S3 thin films [81].Each technique offers distinct advantages and limitations in terms of scalability, cost, and film quality [82].

3.2 Chemical Bath Deposition (CBD)

Chemical bath deposition is one of the most widely used low-temperature techniques for the synthesis of Sb2S3 thin films [83].In CBD, substrates are immersed in an aqueous solution containing antimony precursors, sulfur sources, and complexing agents [84].Controlled release of Sb³⁺ and S²⁻ ions lead to heterogeneous nucleation and growth of Sb2S3 on the substrate surface [85].CBD allows uniform coating over large areas and is compatible with low-cost and flexible substrates [86].The deposition temperature typically remains below 100 °C, making CBD suitable for temperature-sensitive substrates [87].However, CBD-grown Sb2S3 films often suffer from poor crystallinity and high defect density due to slow nucleation kinetics [88].Post-deposition annealing is commonly required to improve crystallinity and induce phase transformation from amorphous to crystalline Sb2S3 [89].Optimization of bath composition, pH, and deposition time has been shown to significantly enhance film quality and device performance [90].

3.3 Spin Coating Technique

Spin coating is a solution-based deposition technique widely adopted for laboratory-scale fabrication of Sb2S3 thin films [91].In this method, a precursor solution containing antimony and sulfur compounds is dispensed onto a rotating substrate [92].Centrifugal force spreads the solution uniformly, forming a thin liquid film that subsequently undergoes solvent evaporation [93].Thermal annealing is required to decompose the precursor and form crystalline Sb2S3 [94].Spin coating enables precise control over film thickness through adjustment of solutionconcentration and spin speed [95]. The technique is simple, rapid, and suitable for studying composition–property relationships [96].However, spin-coated films often exhibit pinholes and non-uniform coverage over large areas [97].Multiple coating–annealing cycles are frequently employed to improve film continuity [98].

3.4 Atomic Layer Deposition (ALD)

Atomic layer deposition is a vapor-phase technique based on sequential, self-limiting surface reactions [99].ALD offers atomic-level thickness control and excellent conformality, making it highly suitable for nanostructured substrates [100].Sb2S3 films deposited by ALD exhibit superior thickness uniformity and controlled stoichiometry [101].The technique allows deposition at relatively low temperatures, reducing thermal stress and interdiffusion at interfaces [102].ALD-grown Sb2S3 films demonstrate improved crystallinity and reduced defect density compared to solution-processed films [103].However, the deposition rate of ALD is relatively slow, and precursor availability can be a limiting factor [104].Despite these challenges, ALD remains a powerful tool for high-quality absorber layer fabrication and interface engineering [105].

3.5 Spray Pyrolysis Technique

Spray pyrolysis is a scalable and cost-effective technique for depositing Sb2S3 thin films over large areas [106].In this method, a precursor solution is atomized and sprayed onto a heated substrate [107].Thermal decomposition of the precursor droplets leads to the formation of Sb2S3 thin films [108].Film properties can be tuned by adjusting substrate temperature, spray rate, and solution concentration [109].Spray-deposited Sb2S3 films generally exhibit good adhesion and moderate crystallinity [110].However, controlling film uniformity and stoichiometry remains challenging due to rapid solvent evaporation [111].Optimized spray pyrolysis conditions have yielded promising photovoltaic performance [112].

3.6 Thermal Evaporation

Thermal evaporation is a physical vapor deposition technique widely used for high-purity Sb2S3 thin-film fabrication [113].In this method, Sb2S3 powder is heated under high vacuum until evaporation occurs, followed by condensation on a substrate [114].Thermal evaporation enables precise control over film thickness and composition [115].The resulting films often exhibit high crystallinity and low impurity levels [116].Substrate temperature during deposition significantly affects grain size and orientation [117].Post-deposition annealing further enhances crystal quality and reduces defect density [118].Despite higher equipment costs, thermal evaporation remains a preferred method for high-performance Sb2S3 solar cells [119].

3.7 Comparative Assessment of Deposition Techniques

Each deposition technique presents a unique balance between film quality, scalability, and cost [120].Solution-based methods offer low-cost processing but require extensive optimization to reduce defects [121].Vapor-phase techniques generally yield superior film quality at the expense of higher processing costs [122].Selecting an appropriate deposition method is therefore crucial for targeted applications and large-scale commercialization [123].

4. Sb2S3-Based Solar Cell Architectures and Device Physics

4.1 Overview of Sb2S3 Photovoltaic Device Architectures

Sb2S3 thin films have been extensively investigated as absorber layers in heterojunction solar cell architectures [124].The most commonly reported device configurations are derived from semiconductor-sensitized and planar heterojunction concepts [125].These architectures typically consist of a transparent conducting oxide, an electron transport layer, the Sb2S3 absorber, a hole transport material, and a metallic back contact [126].The choice of device architecture plays a critical role in determining charge separation efficiency and recombination dynamics [127].Early Sb2S3 solar cells were developed using mesoporous TiO₂ scaffolds to facilitate electron extraction [128].Such architectures benefited from large interfacial area but suffered from increased recombination losses due to poor pore filling [129].Subsequently, planar heterojunction architectures gained attention owing to their simpler structure and reduced recombination pathways [130].Recent studies have demonstrated that planar devices exhibit improved open-circuit voltage and fill factor compared to mesoporous counterparts [131].

Schematic representation of a conventional Sb2S3-based solar cell illustrating the layered device configuration comprising a glass substrate, fluorine-doped tin oxide (FTO) transparent electrode, electron transport layer, Sb2S3 absorber film, hole transport material, and metallic back contact, highlighting the charge-selective junctions within the device [124, 126, 130].

4.2 Electron Transport Layers and Interface Engineering

Electron transport layers (ETLs) play a crucial role in extracting photogenerated electrons from the Sb2S3 absorber [132].Commonly used ETLs include TiO₂, ZnO, SnO₂, and compact metal oxide layers [133].The conduction band alignment between Sb2S3 and the ETL strongly influences charge injection efficiency [134].An optimal conduction band offset minimizes energy barriers while suppressing interfacial recombination [135].Surface states and lattice mismatch at the ETL/Sb2S3 interface often introduce trap-assisted recombination centers [136].

Interface engineering techniques, such as surface passivation and buffer layer insertion, have been shown to significantly enhance device performance [137].Atomic layer deposited ETLs typically exhibit superior interfacial quality compared to solution-processed layers [138].Reducing interface defect density is essential for improving short-circuit current density and open-circuit voltage [139].

4.3 Hole Transport Materials and Back Contacts

Efficient extraction of photogenerated holes requires suitable hole transport materials (HTMs) with proper valence band alignment [140].Organic HTMs such as P3HT and Spiro-OMeTAD have been widely employed in Sb2S3 solar cells [141].Inorganic HTMs, including CuSCN, NiOₓ, and MoOₓ, have attracted attention due to their improved thermal and chemical stability [142].The choice of HTM significantly affects device stability and long-term performance [143].Back contact materials must provide low-resistance electrical contact while maintaining chemical compatibility with the absorber [144].Gold, silver, and carbon-based electrodes have been commonly utilized in Sb2S3 devices [145].Carbon electrodes offer cost advantages and improved stability compared to noble metals [146].

4.4 Charge Generation, Transport, and Recombination Mechanisms

Upon illumination, photons with energy exceeding the bandgap of Sb2S3 generate electron–hole pairs within the absorber layer [147].Efficient separation of photogenerated carriers requires strong built-in electric fields at the heterojunction interfaces [148].Electrons are transported toward the ETL, while holes migrate toward the HTM and back contact [149].Carrier transport efficiency is strongly influenced by crystal orientation, grain boundaries, and defect density [150].Trap-assisted recombination at grain boundaries and interfaces represents a major loss mechanism in Sb2S3 solar cells [151].Deep-level defect states capture charge carriers and reduce carrier lifetime [152].Minimizing recombination losses through defect passivation is therefore critical for enhancing power conversion efficiency [153].

4.5 Energy Band Alignment and Built-In Potential

Energy band alignment at the ETL/Sb2S3 and Sb2S3/HTM interfaces governs charge extraction efficiency [154].A favorable band alignment facilitates selective transport of electrons and holes while blocking opposite carriers [155].Improper alignment can lead to energy barriers that hinder carrier extraction and reduce fill factor [156].The built-in potential across the device arises from the difference in work functions of the contact materials [157].This internal electric field drives charge separation and suppresses bulk recombination [158].Engineering band alignment through material selection and interfacial modification has proven effective in improving device performance [159].

4.6 Photovoltaic Performance Metrics

Key performance parameters of Sb2S3 solar cells include open-circuit voltage, short-circuit current density, fill factor, and power conversion efficiency [160].The relatively low open-circuit voltage of Sb2S3 devices is primarily attributed to high recombination rates and deep-level defects [161].Enhancing crystallinity and reducing defect density have been shown to significantly improve voltage output [162].Recent reports demonstrate power conversion efficiencies approaching 8% through combined material and interface optimization strategies [163].

5. Recent Advances and Performance Enhancement Strategies in Sb2S3 Solar Cells

5.1 Defect Engineering and Passivation Strategies

Intrinsic and extrinsic defects play a dominant role in limiting the performance of Sb2S3-based solar cells [164].Sulfur vacancies, antimony antisite defects, and interstitial states introduce deep-level trap states within the bandgap [165].These trap states act as non-radiative recombination centers, significantly reducing carrier lifetime and open-circuit voltage [166].Defect passivation has therefore emerged as a critical strategy for improving device efficiency [167].Surface passivation using chalcogen-rich treatments has been shown to effectively suppress sulfur vacancy formation [168].Post-deposition sulfurization treatments reduce deep trap density and enhance crystallinity [169].Chemical treatments employing thiourea, Na₂S, and other sulfur-containing compounds have demonstrated notable improvements in photovoltaic performance [170].Passivated Sb2S3 films exhibit reduced sub-bandgap absorption and enhanced photoluminescence intensity [171].

5.2 Doping and Alloying Approaches

Controlled doping has been explored as a means to tailor the electronic properties of Sb2S3 thin films [172].Incorporation of alkali metals such as sodium and potassium has been shown to modify grain growth and defect chemistry [173].Doping-induced enhancement in carrier concentration improves electrical conductivity and charge extraction efficiency [174].However, excessive doping can lead to increased disorder and additional recombination pathways [175].Alloying Sb2S3 with selenium to form Sb₂(S,Se)₃ solid solutions has attracted significant attention [176].Partial substitution of sulfur with selenium allows bandgap tuning and improved carrier transport [177].Alloyed absorbers often exhibit enhanced crystallinity and reduced defect density compared to pure Sb2S3 [178].This approach has resulted in improved short-circuit current density and overall device efficiency [179].

5.3 Interface Engineering and Buffer Layer Optimization

Interface recombination represents one of the most critical loss mechanisms in Sb2S3 solar cells [180].Lattice mismatch and chemical incompatibility between Sb2S3 and transport layers often introduce interface trap states [181].Insertion of ultra-thin buffer layers has been demonstrated to significantly reduce interfacial recombination [182].Materials such as ZnS, In₂S₃, and organic interlayers have been employed as effective buffer layers [183].Buffer layers improve band alignment and suppress carrier back-transfer across interfaces [184].Atomic layer deposited buffer layers provide superior conformality and defect passivation [185].Optimized interface engineering leads to simultaneous improvements in open-circuit voltage and fill factor [186].

.5.4 Morphology Control and Grain Orientation Engineering

Film morphology and grain orientation critically influence charge transport and recombination behavior in Sb2S3 thin films [187].Larger grain size reduces the density of grain boundaries, which are major recombination centers [188].Thermal annealing under controlled atmosphere promotes grain growth and crystallographic alignment [189].Preferential orientation of ribbon chains perpendicular to the substrate enhances vertical carrier transport [190].Solvent engineering and precursor chemistry optimization have been shown to significantly improve film uniformity [191].Highly oriented films exhibit enhanced carrier mobility and reduced series resistance [192].Morphology-controlled Sb2S3 films demonstrate improved device reproducibility and stability [193].

5.5 Device Stability and Environmental Robustness

Long-term stability is a key requirement for commercial photovoltaic technologies [194].Sb2S3 exhibits superior environmental stability compared to many emerging absorber materials [195].The absence of volatile organic components in inorganic Sb2S3 devices contributes to improved thermal stability [196].Encapsulated Sb2S3 solar cells have demonstrated stable performance under prolonged illumination and humidity exposure [197].Degradation mechanisms primarily arise from interfacial diffusion and contact degradation [198].Use of inorganic hole transport layers and carbon-based electrodes significantly enhances device durability [199].Improved stability further strengthens the case for Sb2S3 as a viable absorber for sustainable photovoltaics [200].

5.6 Performance Trends and Efficiency Progress

Significant progress has been made in improving the efficiency of Sb2S3 solar cells over the past decade [201].Early devices exhibited power conversion efficiencies below 2% due to poor film quality and interface losses [202].Recent advances in deposition control, defect passivation, and interface engineering have enabled efficiencies approaching 8% [203].Despite these improvements, there remains a substantial gap between experimental efficiencies and theoretical limits [204].

6. Challenges, Limitations, and Future Research Directions

6.1 Fundamental Challenges in Sb2S3 Thin-Film Solar Cells

Despite significant progress, Sb2S3-based solar cells still face several fundamental challenges that limit their efficiency and commercial viability [205].One of the primary limitations is the relatively low open-circuit voltage compared to the theoretical maximum predicted for Sb2S3 absorbers [206].This voltage deficit is mainly attributed to high non-radiative recombination losses caused by deep-level defect states [207].Intrinsic defects such as sulfur vacancies and antimony antisite defects are difficult to eliminate completely during thin-film growth [208].Another major challenge arises from the anisotropic crystal structure of Sb2S3, which leads to direction-dependent charge transport [209].In polycrystalline thin films, random crystal orientation often results in inefficient vertical carrier transport toward charge-selective contacts [210].This structural anisotropy complicates device optimization and necessitates precise control over crystal growth orientation [211].Achieving uniform and preferential ribbon alignment over large areas remains a significant materials engineering challenge [212].

6.2 Interface-Related Losses and Contact Instability

Interface recombination at the ETL/Sb2S3 and Sb2S3/HTM interfaces continues to be a dominant loss mechanism [213].Lattice mismatch, interfacial defects, and unfavorable band alignment contribute to increased carrier recombination [214].Chemical instability at the back contact interface can also lead to long-term device degradation [215].Diffusion of metal atoms into the Sb2S3 absorber under operational conditions has been reported to deteriorate device performance [216].The selection of stable and chemically compatible contact materials remains a critical challenge [217].Organic hole transport materials often suffer from poor thermal and environmental stability [218].Replacing organic components with robust inorganic alternatives is therefore a key research priority [219].

6.3 Scalability and Manufacturing Constraints

While high-quality Sb2S3 films have been demonstrated at the laboratory scale, translating these results to large-area devices presents additional challenges [220].Solution-based deposition techniques often exhibit poor thickness uniformity and reproducibility over large substrates [221].Vapor-phase techniques, although capable of producing high-quality films, involve higher capital and operational costs [222].Balancing film quality with scalable, cost-effective manufacturing processes remains unresolved [223].Process integration with existing photovoltaic manufacturing infrastructure also poses challenges [224].Compatibility with roll-to-roll processing and flexible substrates requires further optimization of deposition conditions [225].Developing scalable deposition methods without compromising film quality is essential for commercialization [226].

6.4 Future Research Directions

Future research on Sb2S3 solar cells should prioritize comprehensive defect control strategies at both bulk and interface levels [227].Advanced characterization techniques, such as deep-level transient spectroscopy and time-resolved photoluminescence, are needed to identify dominant recombination pathways [228].Combining experimental studies with first-principles modeling can provide deeper insights into defect formation and passivation mechanisms [229].Orientation-controlled growth of Sb2S3 thin films represents a promising pathway to enhance charge transport [230].Techniques that promote vertical alignment of ribbon chains are expected to significantly improve carrier extraction efficiency [231].Interface engineering using ultra-thin passivation layers and graded band structures should be further explored [232].Alloying and compositional engineering offer additional opportunities to optimize bandgap and electronic properties [233].Controlled incorporation of selenium or other chalcogen elements may enable improved carrier transport and reduced recombination [234].Exploration of tandem device architectures incorporating Sb2S3 as a wide-bandgap absorber could unlock higher overall efficiencies [235].

6.5 Commercialization Prospects

Sb2S3 possesses several intrinsic advantages that make it attractive for commercial photovoltaic applications [236].The material is composed of earth-abundant and non-toxic elements, ensuring long-term sustainability [237].Its high absorption coefficient allows for ultrathin absorber layers, reducing material consumption [238].Furthermore, Sb2S3 exhibits superior environmental stability compared to many emerging absorber materials [239].However, closing the efficiency gap with established thin-film technologies remains essential for market competitiveness [240].Continued improvements in efficiency, stability, and scalability will determine the future commercial success of Sb2S3 solar cells [241].With sustained research efforts and technological innovation, Sb2S3 holds strong potential as a next-generation photovoltaic absorber [242].

7. Conclusion

Antimony sulfide (Sb2S3) has emerged as a highly promising absorber material for next-generation thin-film photovoltaic applications due to its earth-abundant composition, low toxicity, and favorable optoelectronic properties [243].The orthorhombic crystal structure composed of quasi-one-dimensional (Sb₄S₆)ₙ ribbon chains impart strong anisotropy to charge transport, which fundamentally governs device performance [244].Its suitable bandgap in the visible range and exceptionally high optical absorption coefficient enables efficient light harvesting using ultrathin absorber layers [245].This review has comprehensively analyzed the structure–property–performance relationships of Sb2S3 thin films, emphasizing the critical role of deposition techniques, crystal orientation, and defect chemistry [246].Both solution-based and vapor-phase deposition methods have demonstrated the capability to produce functional Sb2S3 absorber layers, though trade-offs between scalability, cost, and film quality remain [247].Advances in deposition control, post-treatment processes, and annealing strategies have significantly improved crystallinity and reduced defect densities [248].Considerable progress has been achieved in Sb2S3-based solar cell architectures through interface engineering, buffer layer optimization, and selective contact design [249].Defect passivation strategies, including sulfur-rich treatments and compositional engineering, have proven effective in suppressing non-radiative recombination losses [250].Doping and alloying approaches, particularly the formation of Sb₂(S,Se)₃ solid solutions, offer promising pathways for bandgap tuning and enhanced carrier transport [251].Despite these advancements, Sb2S3 solar cells continue to exhibit a notable efficiency gap compared to their theoretical limits [252].This gap is primarily attributed to residual bulk and interfacial defects, sub-optimal band alignment, and anisotropy-induced transport limitations [253].Addressing these challenges requires precise control over crystal growth orientation, advanced defect characterization, and rational interface design [254].Looking forward, future research should focus on orientation-controlled thin-film growth, atomic-scale interface passivation, and integration of robust inorganic charge transport layers [255].The exploration of tandem and hybrid photovoltaic architectures incorporating Sb2S3 as a wide-bandgap absorber represents a particularly promising direction [256].With continued interdisciplinary efforts combining materials science, device physics, and scalablemanufacturing, Sb2S3 holds strong potential to evolve into a commercially viable photovoltaic technology [257].

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