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Formamidinium lead triiodide (FAPbI3) perovskite without methylammonium and/or Cs cations is considered the most promising candidate for perovskite photovoltaics. However, the crystallization of photoactive α‐FAPbI3 requires high‐temperature annealing (≥150 °C) and a controlled humidity environment when methylammonium‐containing additives are absent. A methylammonium‐free ink is reported that enables low‐temperature (≤80 °C) crystallization of photoactive α‐FAPbI3 films, while also demonstrating compatibility with blade‐coating large‐area films in ambient air. The synergistical effects of methylphenyl sulfoxide and PbCl2 facilitate the formation of an intermediate phase of nanoscale‐disordered δ‐FAPbI3, which dramatically reduces the crystallization temperature of α‐FAPbI3 down to 80 °C and even below. The 80 °C crystalized α‐FAPbI3 exhibits reduced strain and improved uniformity compared to high‐temperature annealed counterparts. The synthesized ink and the corresponding intermediate precursor film are also found remarkably stable, allowing open‐air processing without the need for humidity control. Highly efficient n–i–p structured α‐FAPbI3 minimodules can be fabricated under an ambient environment RH 50% with the ink at 80 °C, achieving a power conversion efficiency of up to 22.4%. The discovery of the low‐temperature FAPbI3 ink paves a new avenue for printing perovskite solar cells and associated optoelectronic applications, accelerating the commercialization progress of perovskite materials. [ABSTRACT FROM AUTHOR]

Multidimensional simulations for diverse solar cells often encounter distinctive configurations, even when employing the same simulation software. The complexity and inefficiency of this process are further exacerbated when employing different simulators. From our extensive decade‐long experience in numerical simulations of diverse solar cells, we have identified ten common simulation steps intrinsic to typical electrical and optical simulations. Subsequently, we propose ten sets of variables that encompass all the relevant details required for these steps. To address the challenge of varying information requirements for each variable across different simulations, we assign a list, a versatile data type, to each variable. This approach, by design, enables concise, coherent, and flexible input, accommodating the unique demands of each simulation. However, to ensure unambiguous simulations, precise specifications for these variables are essential. Computer code has been successfully implemented to ensure adherence to specifications and expedite variable synchronization with Sentaurus, the de facto standard for device simulation. Within this framework, users are only tasked with editing variables in a plain text file, obviating the need for in‐depth knowledge of Sentaurus. This streamlines the prerequisites for engaging in numerical simulation significantly. Through thoughtful design considerations, we preserve the simulation capacity while simultaneously enhancing productivity considerably. This open‐source framework welcomes global collaboration within the photovoltaic community and has the potential to generate an extensive dataset for cost‐effective artificial intelligence training. [ABSTRACT FROM AUTHOR]

Kesterite is an earth‐abundant energy material with high predicted power conversion efficiency, making it a sustainable and promising option for photovoltaics. However, a large open circuit voltage Voc deficit due to non‐radiative recombination at intrinsic defects remains a major hurdle, limiting device performance. Incorporating Ge into the kesterite structure emerges as an effective approach for enhancing performance by manipulating defects and morphology. Herein, how different amounts of Ge affect the kesterite growth pathways through the combination of advanced microscopy characterization techniques are systematically investigated. The results demonstrate the significance of incorporating Ge during the selenization process of the CZTSSe thin film. At high temperature, the Ge incorporation effectively delays the selenization process due to the formation of a ZnSe layer on top of the metal alloys through decomposition of the Cu‐Zn alloy and formation of Cu‐Sn alloy, subsequently forming of Cu‐Sn‐Se phase. Such an effect is compounded by more Ge incorporation that further postpones kesterite formation. Furthermore, introducing Ge mitigates detrimental "horizontal" grain boundaries by increasing the grain size on upper layer. The Ge incorporation strategy discussed in this study holds great promise for improving device performance and grain quality in CZTSSe and other polycrystalline chalcogenide solar cells. [ABSTRACT FROM AUTHOR]

Poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine (PTAA) is one of the most efficient hole transport materials for p–i–n structured perovskite solar cells (PSCs). However, the hydrophobicity of PTAA causes wettability problems and is thereby associated with low yield and poor reproducibility. Herein, a new strategy for improving the perovskite precursor wettability on PTAA is developed. A Cu2(Thiourea)Br2 complex interfacial layer is introduced on the PTAA, improving the coverage of perovskite precursors and thereby the perovskite film. Partially dissolved Cu2(Thiourea)Br2 in the perovskite absorber further enhances band alignment and carrier extraction between layers. With the addition of Cu2(Thiourea)Br2 layer on nondoped PTAA, PSCs in p–i–n structure with a bandgap of 1.63 eV have achieved over 21% efficiency both on 0.1 and 1.0 cm2 sized devices with a significantly improved yield and reproducibility. Unencapsulated devices retain 100% of their initial efficiency after 2000 h at 65 °C. [ABSTRACT FROM AUTHOR]

Tandem solar cells are rationally designed and fabricated by stacking multiple subcells to achieve power conversion efficiency well above the Shockley‐Queisser (SQ) limit. There is a large selection pool for the subcell candidates, such as Si, III–V, Kesterite, Perovskite, and organic solar cells. A series of different combinations of these subcells have been successfully demonstrated in practical tandem solar cell devices. However, there has not been a systematic summary of how to connect subcells in a tandem solar cell using a practical, cost‐effective, and efficiency‐beneficial fashion. In this work, the connection manners of subcells within a tandem cell are classified into three main categories, performing sequential growth, using the physical connection, and applying an intermediate layer, focusing on systematical description of intermediate layers using different materials. The advantages and disadvantages of these connection methods and their applicability to tandem cell types are further elaborated using two typical example models, III–V/Si and Perovskite inclusive tandem cell devices. Eventually, this work can provide useful guidance on how to carry out a suitable intermediate connection in the design of tandem solar cells depending on the selected subcells and device structure. [ABSTRACT FROM AUTHOR]

Flexible photovoltaics have been and will be increasingly in demand in modern and future society in various applications. Searching for ideal flexible photovoltaic technologies that can perfectly meet these expanding demands has long been an active branch of photovoltaic research. Flexible kesterite Cu2ZnSn(S,Se)4 (CZTSSe) has emerged in recent years owning to its great potential to be an abundant, low-cost, stable, and high-efficiency 'green' photovoltaic material that can be widely deployed with the lowest detrimental environmental impact. Here, we review the recent progress with flexible kesterite solar cells in thin-film and monograin technologies, discuss the key challenges and strategies associated with the flexible substrates, and finally provide the future perspectives on further pushing the efficiency toward commercial-competitive levels. [ABSTRACT FROM AUTHOR]

Kesterite Cu2ZnSn(S,Se)4 (CZTSSe) with earth‐abundant and environmental‐benign constituents has been regarded as a promising solar energy harvesting material for green and cost‐effective photovoltaic applications. The record efficiency of CZTSSe solar cells has recently been refreshed twice after years‐long stagnation, keeping it in the spotlight. Nevertheless, the champion efficiency of 13.6% is still far behind its counterpart Cu(In,Ga)Se2 (CIGS) (23.35%) despite being endowed with a similar electronic structure and nearly‐identical device architecture. In fact, CZTSSe solar cells are more susceptible to non‐radiative recombination at bulk and interfaces, which must be improved for further efficiency advancement. In this review, the state‐of‐art strategies to enhance the power conversion efficiency of CZTSSe solar cells are summarized and discussed, with focus given to three critical device regions i) kesterite absorber, ii) buffer/kesterite interface, and iii) kesterite/back contact interface. With the further elucidation of the latest progress and disclosure of fundamental mechanisms, novel insights toward high‐efficiency kesterite solar cells are proposed. [ABSTRACT FROM AUTHOR]

Earth‐abundant and air‐stable Cu2BaSnS4−xSex (CBTSSe) and related thin‐film absorbers are regarded as prospective options to meet the increasing demand for low‐cost solar cell deployment. Devices based on vacuum‐deposited CBTSSe absorbers have achieved record power conversion efficiency (PCE) of 5.2% based on a conventional device structure using CdS buffer and i‐ZnO/indium tin oxide (ITO) window layers, with open‐circuit voltage (VOC) posing the major bottleneck for improving solar cell performance. The current study demonstrates a >20% improvement in VOC (from 0.62 to 0.75 V) and corresponding enhancement in PCE (from 5.1% to 6.2% without antireflection coating; to 6.5% with MgF2 antireflection coating) for solution‐deposited CBTSSe solar cells. This performance improvement is realized by introducing an alternative successive ionic layer adsorption and reaction‐deposited Zn1−xCdxS buffer combined with sputtered Zn1−xMgxO/Al‐doped ZnO window/top contact layer, which offers lower electron affinities relative to the conventional CdS/i‐ZnO/ITO stack and better matching with the low electron affinity of CBTSSe. A combined experimental (temperature‐ and light intensity‐dependent VOC measurements) and device simulation (SCAPS‐1D) evaluation points to the importance of addressing relative band offsets for both the buffer and window layers relative to the absorber in mitigating interfacial recombination and optimizing CBTSSe solar cell performance. [ABSTRACT FROM AUTHOR]

Effectively incorporating alkali metals or alternative isovalent cations into Cu2ZnSnS4 (CZTS) is considered one of the most promising strategies for realizing a step‐change improvement in the photovoltaic device performance. Herein, the local distribution of Na and Cd by a moisture‐assisted postdeposition annealing (MAPDA) treatment combined with a subsequent heterojunction heat treatment is manipulated. The MAPDA treatment facilitates the controllable reduction of the Na concentration, thus promoting the spontaneous diffusion of Cd into the heterojunction region. A subsequent 150 °C low‐temperature heterojunction heat treatment after MAPDA treatment enables further modification of Cd and Na distributions, leading to significantly enhanced optoelectronic properties at the CZTS/CdS heterojunction and greatly improved device performance with a peak conversion efficiency of 9.40%. The modified heterojunction significantly improves quasi‐Fermi‐level splitting under low‐photon injection, making CZTS solar cells more feasible in low‐light applications. This work provides an effective approach to simultaneously manipulate the distribution of Na and Cd, enabling pronounced modification of the heterojunction quality of CZTS solar cells and boost of conversion efficiencies. Insights gleaned herein may also be applicable to manipulating other critical trace elements in chalcogenide materials in general. [ABSTRACT FROM AUTHOR]

Antimony sulfide (Sb2S3) is a promising wide‐bandgap photovoltaic material, and a potential top‐cell candidate for next‐generation Si‐based tandem solar cells. The most widely used electron transport layers in Sb2S3 solar cells are TiO2 and CdS, which present an obvious performance variation in open‐circuit voltage (VOC) and short current (Jsc). However, the mechanisms behind the performance disparity because of the electron transport layer (ETL) have not been disclosed. Herein, a comprehensive comparative study of using TiO2 and CdS as the electron transport layers in Sb2S3 solar cells is presented, which covers their influence on preferential crystal orientation, band alignment, interface, and bulk defects. It is found that the CdS ETL results in less interfacial defects and more favorable band alignment, enabling a higher VOC, while the high resistance of the CdS film and parasitic light absorption restricts the JSC. The findings provide a substantial guidance on device optimization for Sb2S3 solar cells. [ABSTRACT FROM AUTHOR]

Sulfide kesterite Cu2ZnSnS4 (CZTS) solar cells, containing earth‐abundant and environmentally benign constituents, are regarded as promising candidates for thin‐film photovoltaic technologies. CZTS device performance, however, is currently limited by severe nonradiative recombination caused by abundant deep‐level defects. Herein, an effective defect engineering approach for high bandgap CZTS solar cells using a newly introduced moisture‐assisted post‐deposition annealing treatment is reported. This treatment modifies the local chemical composition within the heterojunction and CZTS grain boundaries and enhances the incorporation of Cd within the CZTS layer during CdS deposition. Cd not only accumulates at the grain boundaries, but it also presents in grain interiors where it occupies Cu lattice sites. The overall modification of the local chemical environment suppresses deep level defects and activates relatively shallow acceptor CuZn antisites and Cu vacancies, giving rise to remarkably improved device performance. This work opens a new direction for defect engineering of kesterite materials, which may also be applicable to other thin film semiconductors. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) with a power conversion efficiency (PCE) overpassing 25% have proved to be the most promising competitor for the next‐generation photovoltaic technology. Massive efforts are devoted to the improvement of the performance and stability of PSCs, whereas the hole transport layer (HTL) has attracted significant interest. Among diverse hole transport materials, poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine (PTAA) is one of the most promising candidates due to its ease of fabrication, transparency to visible light, mechanical flexibility, conductivity, and stability. Over the past few years, there has been an increasing amount of research using PTAA as the HTL first in n–i–p and then in p–i–n PSCs with extended applications in flexible, large‐area, and tandem devices. Herein, a progress review on PTAA for PSC applications is provided, which enables a better understanding of the advantages and disadvantages of PTAA, as well as the approaches to fully realizing its tremendous potential. The emerging and promising research directions for PTAA‐based PSCs are discussed, shedding light on the practical applications of PTAA. [ABSTRACT FROM AUTHOR]

Consolidated tables showing an extensive listing of the highest independently confirmed efficiencies for solar cells and modules are presented. Guidelines for inclusion of results into these tables are outlined, and new entries since January 2022 are reviewed. An appendix describing temporary electrical contacting of large‐area solar cells approaches and terminology is also included. [ABSTRACT FROM AUTHOR]

Antimony sulfide is an emerging 1D nontoxic Earth‐abundant photovoltaic material with favorable wide bandgap as a suitable top‐cell candidate for multijunction tandem solar cells. However, the current fabrication technology for Sb2S3 solar cells relies heavily on a high‐purity Sb2S3 source, which limits its large‐scale deployment. Therefore, it is attractive to fabricate the Sb2S3 solar cells directly from the raw stibnite source, which can be cost effective by avoiding the complicated, costly purification and refinement process of the stibnite ore, while reducing process‐emitted pollution. Herein, high‐quality Sb2S3 films (thickness: ≈1 μm) by the vapor transport deposition of raw stibnite ore powder are obtained, followed by a sulfurization process to remove the surface oxides and facilitate alkali element redistribution. In this way, the particle size is increased from ≈500 nm to ≈1.5 μm, the carrier concentration of the Sb2S3 film is increased from ≈1015 to ≈1016 cm−3, and the power conversion efficiency of Sb2S3 solar cell is increased by more than two times. Through the elemental distribution analysis, it is found that it is the redistribution of alkali elements introduced from the natural stibnite ore that induces the grain growth, contributes toward defect suppression, and leads toward enhanced device performance. [ABSTRACT FROM AUTHOR]

Selective contact annealing is developed to improve the performance of bifacial‐grid III–V top cells bonded on glass by epoxy resin for Si‐based tandem solar cells. The annealing method can minimize the damage to the bonding layer and is compatible with the industrial evaporation technique for contact fabrication. The improvement of the front contact quality by selective annealing treatments is demonstrated through optical and electrical characterization which shows a significantly enhanced III–V device performance. Furthermore, a fitting model is established to reveal the mechanism underlying the performance improvement through the reduction of contact resistances and the bad contact area. Herein, an effective annealing approach to fabricate high‐quality metal–semiconductor contacts for devices with poor thermal resistivity is demonstrated, which can be used in polymer‐bonded top cells in Si‐based tandem solar cells and other flexible optoelectronic devices on polymer substrates. [ABSTRACT FROM AUTHOR]

Herein, an electroluminescence (EL)‐based imaging method to detect broken fingers in solar cells is presented. The method is based on the ratio of two EL images taken with different paths of the injected current. The resultant high‐contrast images allow unambiguous separation of various series resistance‐related problems and hence the potential application of identifying broken fingers. The method can be applied to solar cells with both full and partial rear contacts. It can be easily implemented in commercial luminescence imaging systems, significantly extending their capabilities. [ABSTRACT FROM AUTHOR]

Kesterite Cu2ZnSnS4 (CZTS) solar cell has emerged as one of the most promising thin‐film photovoltaic technologies that allows for cheap, clean, and efficient renewable power in the future. Nevertheless, limited by the large photovoltage deficit caused by severe interface recombination, the potential of CZTS solar cells is far from being fully tapped. Herein, it is demonstrated that the carrier density of the CZTS absorber and the acceptor‐like interface defects are two critical factors governing the interface recombination in addition to the unfavorable conduction band alignment. Results of device simulation suggest that passivating the acceptor‐like interface defects combined with appropriate absorber carrier density is the essential way to promote the photovoltage and efficiency of CZTS solar cells to a more competitive level. It is believed that these results could be generally applicable to the interface recombination of other heterojunction solar cells. [ABSTRACT FROM AUTHOR]

The performance of kesterite Cu2ZnSn(S,Se)4 (CZTSSe) solar cell is known to be severely limited by the nonradiative recombination near the heterojunction interface and within the bulk of the CZTSSe absorber resulting from abundant recombination centers and limited carrier collection efficiency. Herein, nonradiative recombination is simultaneously reduced by incorporating small amounts of Ge and Cd into the CZTSSe absorber. Incorporation of Ge effectively increases the p‐type doping, thus successfully improving the bulk conductance and reducing the recombination in the CZTSSe bulk via enhanced quasi‐Fermi level splitting, while the incorporation of Cd greatly reduces defects near the junction region, enabling larger depletion region width and better carrier collection efficiency. The combined effects of Cd and Ge incorporation give rise to systematic improvement in open‐circuit voltage (VOC), short‐circuit current density (JSC), and fill factor (FF), enabling a high conversion efficiency of 11.6%. This study highlights the multiple cation incorporation strategy for systematically manipulating the opto‐electronic properties of kesterite materials, which may also be applicable to other semiconductors. [ABSTRACT FROM AUTHOR]

Earth‐abundant and environmentally benign kesterite Cu2ZnSn(S,Se)4 (CZTSSe) is a promising alternative to its cousin chalcopyrite Cu(In,Ga)(S,Se)2 (CIGS) for photovoltaic applications. However, the power conversion efficiency of CZTSSe solar cells has been stagnant at 12.6% for years, still far lower than that of CIGS (23.35%). In this report, insights into the latest cutting‐edge strategies for further advance in the performance of kesterite solar cells is provided, particularly focusing on the postdeposition thermal treatment (for bare absorber, heterojunction, and completed device), alkali doping, and bandgap grading by engineering graded cation and/or anion alloying. These strategies, which have led to the step‐change improvements in the power conversion efficiency of the counterpart CIGS solar cells, are also the most promising ones to achieve further efficiency breakthroughs for kesterite solar cells. Herein, the recent advances in kesterite solar cells along these pathways are reviewed, and more importantly, a comprehensive understanding of the underlying mechanisms is provided, and promising directions for the ongoing development of kesterite solar cells are proposed. [ABSTRACT FROM AUTHOR]

Halide perovskite‐based photovoltaic (PV) devices have recently emerged for low energy consumption electronic devices such as Internet of Things (IoT). In this work, an effective strategy to form a hole‐selective layer using phenethylammonium iodide (PEAI) salt is presented that demonstrates unprecedently high open‐circuit voltage of 0.9 V with 18 µW cm−2 under 200 lux (cool white light‐emitting diodes). An appropriate post‐deposited amount of PEAI (2 mg) strongly interacts with the perovskite surface forming a conformal coating of PEAI on the perovskite film surface, which improves the crystallinity and absorption of the film. Here, Kelvin probe force microscopy results indicate the diminished potential difference across the grain boundaries and grain interiors after the PEAI deposition, constructing an electrically and chemically homogeneous surface. Also, the surface becomes more p‐type with a downshift of a valence band maximum, confirmed by ultraviolet photoelectron spectroscopy measurement, facilitating the transport of holes to the hole transport layer (HTL). The hole‐selective layer‐deposited devices exhibit reduced hysteresis in light current density–voltage curves and maintain steadily high fill factor across the different light intensities (200–1000 lux). This work highlights the importance of the HTL/perovskite interface that prepares the indoor halide perovskite PV devices for powering IoT device. [ABSTRACT FROM AUTHOR]

Lithium incorporation in kesterite Cu2ZnSn(S,Se)4 (CZTSSe) materials has been experimentally proven effective in improving electronic quality for application in photovoltaic devices. Herein, a feasible and effective solution‐based lithium post‐deposition treatment (PDT), enabling further efficiency improvement on the high‐performance baseline is reported and the dominant mechanism for this improvement is proposed. In this way, lithium is uniformly incorporated into grain interiors (GIs) without segregation at grain boundaries (GBs), which can occupy the Zn sites with a high solubility in the CZTSSe matrix, producing high density of LiZn antisites with shallower acceptor levels than the intrinsic dominant defect (CuZn antisites). As a result, CZTSSe absorber with better p‐type doping is obtained, leading to a pronounced enhancement in fill factor and a corresponding gain in open‐circuit voltage and short‐circuit current and consequently a significant efficiency boost from 9.3% to 10.7%. This work provides a feasible alternative alkali‐PDT treatment for chalcogenide semiconductors and promotes a better understanding of the mechanism of Li incorporation in kesterite materials. [ABSTRACT FROM AUTHOR]

Majority carrier mobility is one of the most fundamental and yet important carrier transport parameters determining the optimal device architecture and performance of the emerging antimony chalcogenide solar cells. However, carrier mobility measurements based on the Hall effect have limitations for these highly anisotropy materials due to the discrepancy of transport directions under Hall measurement and device operation. Herein, a defect‐resolved mobility measurement (DRMM) method enabling the evaluation of effective majority carrier mobility from a working device without such limitations is presented. Using this method, comprehensive information about the carrier transport in representative Sb2S3 and Sb2Se3 solar cells is extracted. Though with preferred [hk1]‐crystalline orientation, Sb2S3 and Sb2Se3 still suffer from extremely low carrier mobility and low carrier density, respectively, resulting in large bulk resistance and poor carrier collection efficiency. Further crystalline structure analysis discloses that crystalline defects such as dislocations may significantly constrain carrier transport in these low‐dimensional materials. These results suggest that a p‐i‐n device architecture with fully depleted absorber is a promising optimization approach for further efficiency advances of antimony chalcogenide solar cells. [ABSTRACT FROM AUTHOR]

For semitransparent devices with n‐i‐p structures, a metal oxide buffer material is commonly used to protect the organic hole transporting layer from damage due to sputtering of the transparent conducting oxide. Here, a surface treatment approach is addressed for tungsten oxide‐based transparent electrodes through slight modification of the tungsten oxide surface with niobium oxide. Incorporation of this transparent electrode technique to the protective buffer layer significantly recovers the fill factor from 70.4% to 80.3%, approaching fill factor values of conventional opaque devices, which results in power conversion efficiencies over 18% for the semitransparent perovskite solar cells. Application of this approach to a four‐terminal tandem configuration with a silicon bottom cell is demonstrated. [ABSTRACT FROM AUTHOR]

Solar energy is one of the most abundant renewable energy sources. For efficient utilization of solar energy, photovoltaic technology is regarded as the most important source. However, due to the intermittent and unstable characteristics of solar radiation, photoelectric conversion (PC) devices fail to meet the requirements of continuous power output. With the development of rechargeable electric energy storage systems (ESSs) (e.g., supercapacitors and batteries), the integration of a PC device and a rechargeable ESS has become a promising approach to solving this problem. The so‐called integrated photorechargeable ESSs which can directly store sunlight generated electricity in daylight and reversibly release it at night time, has a huge potential for future applications. This review summarizes the development of several types of mainstream integrated photorechargeable ESSs and introduces different working mechanisms for each photorechargeable ESS in detail. Several general perspectives on challenges and future development in the field are also provided. [ABSTRACT FROM AUTHOR]

A proof‐of‐concept tandem solar cell using Sb2S3 and Sb2Se3 as top and bottom cell absorber materials is demonstrated. The bandgaps of Sb2S3 and Sb2Se3 are 1.74 and 1.22 eV, perfectly satisfying the requirement of tandem solar cells. The application of few‐layer graphene enables high transmittance and excellent interfacial contact in the top subcell. By controlling the thickness of the top cell for maximizing the spectral application, the tandem device delivers a power conversion efficiency of 7.93%, which outperforms the individually optimized top cell (5.58%) and bottom cell (6.50%). Mechanistical investigation shows that the tandem device is able to make up voltage loss in the subcells, which is a critical concern in the current antimony chalcogenide solar cells. This study provides an alternative approach to enhancing the energy conversion efficiency of antimony selenosulfide. [ABSTRACT FROM AUTHOR]

Environmentally friendly and earth abundant Cu2ZnSnS4 (CZTS) based thin films are potential absorbers for next generation photovoltaics. Their optical properties provide the option to be used as upper cells for Si based tandem solar cells, together with a similar structure to Si, triggering interest in investigation of CZTS/Si tandem cells. However, epitaxially growing CZTS on Si can be challenging. Here, we heteroepitaxially grow tetragonal Cu2ZnSnS4 (CZTS) thin films on single crystalline cubic Si (111) wafers with a 4° miscut by simple and low-cost radio frequency magnetron sputtering from a single target. The CZTS film displays a mirror-like surface with a surface roughness of 8.46 nm. The absorption coefficients of the epitaxial CZTS are over 104 cm−1 at 1.5 eV and 1.0 × 105 cm−1 at 2.1 eV. The bandgap is 1.45 eV, and the photoluminescence lifetime is 7.04 ns. Our results demonstrate the potential of the epitaxial CZTS films fabricated by sputtering on the Si substrate for application in CZTS/Si based tandem solar cells. [ABSTRACT FROM AUTHOR]

To improve the crystallinity and overall film quality of the light absorbing layer is vital to further enhance the performance of sulfide Kesterite Cu2ZnSnS4 (CZTS) solar cells, especially for all solution‐processed devices using ball‐milling processed CZTS that generally leads to poor crystallization. In this work, a novel treatment method involving high‐boiling‐point solvent (HBPS), via simply spinning oleic acid (OA) solution onto CZTS precursor film coupled with an elongated annealing duration, was for the first time reported that enabled not only reduced surface roughness, but considerably increased crystalline of CZTS film. This is corroborated by an enhanced XRD intensity by eight ‐fold in conjunction with a five‐fold increased steady‐state PL intensity, the latter of which also indicates an improved CdZnS/CZTS heterojunction quality. Combined with all solution‐processed buffer layer and contact material, device using HBPS‐treated ball‐milling processed CZTS absorber yielded a power conversion efficiency of 6.1%, which is the highest reported for all solution‐processed pure‐sulfide CZTS solar cells. The HBPS‐treatment approach developed in this work is simple and effective, and in principle can promisingly be applied to any film to work synergistically with thermal annealing treatment, leading to simultaneously enhanced crystallinity and overall film quality while maintaining its planeness. A one‐step high‐boiling‐point solvent treating method is developed to form nearly micron‐sized pure‐sulfide Cu2ZnSnS4 large grains. Oleic Acid is spin‐coated onto CZTS precursor before annealing, combining with extended annealing duration, to enhance crystallinity, enlarge grain size and reduce surface roughness of CZTS film simultaneously. Based on this high‐boiling‐point solvent treatment. all solution‐processed (sputtering‐free) CZTS solar cell achieves competitive photovoltaic performance. [ABSTRACT FROM AUTHOR]

The earth‐abundant and environmentally‐friendly CuSbS2 solar cells have been struggling with low device performance, especially poor open circuit voltage (Voc). In this work, post‐annealing treatment of the CuSbS2/CdS heterojunction performed on CuSbS2‐based solar cells was firstly reported. With this treatment, we demonstrated CuSbS2 solar cells with a record Voc of 622 mV. The improvement of device performance was found peaked at 250°C post‐annealing which mainly benefits from the significantly boosted open‐circuit voltage and short‐circuit current. The study of microstructure by high‐resolution transmission electron microscopy revealed that such improvement could be attributed to the formation of epitaxial CuSbS2/CdS hetero‐interface upon heat treatment, which reduces the interface defect density that may lead to reduced Voc deficit. Besides, results of photoluminescence and time‐resolved photoluminescence measurements also indicated improved electrical properties of completed devices with higher photoluminescence intensity and longer minority carrier lifetime. We demonstrated significant improvement in efficiency (particularly in the Voc and Jsc) for CuSbS2 solar cells by post‐heat treatment of the CuSbS2/CdS heterojunction. The underlying correlation between post‐heat treatment and device performance reveals that the post‐heat treatment on the heterojunction leads to (1) the transformation from amorphous to epitaxial relationship of CuSbS2/CdS hetero‐interface and (2) simultaneously improved absorber quality. [ABSTRACT FROM AUTHOR]

Abstract: In this research, a new route of surface passivation is reported by introducing hydrogen from the atomic layer deposited (ALD) Al2O3 layer into pure sulfide Cu2ZnSnS4 (CZTS) solar cells. Different amounts of hydrogen are incorporated into the Cu2ZnSnS4/CdS interface through controlling the thickness of the ALD‐Al2O3 layer. The device with three cycles of ALD‐Al2O3 yields the highest efficiency of 8.08% (without antireflection coating) with improved open‐circuit voltage of up to 70 mV. With closer examination on the passivation route of ALD‐Al2O3, it is revealed by the surface chemisty study that the Al2O3 can be etched away by ammonium hydroxide in the CdS buffer deposition process. Instead, the hydrogen is detected within a shallow depth from the CZTS surface, and makes a significant difference in the measured distribution of contact potential difference and device performance. This may be interpreted by the effect of hydrogen passivation of the CZTS surface by curing dangling bonds at the surface of CZTS grains. This work may provide a new direction of further improving the performance of kesterite solar cells. [ABSTRACT FROM AUTHOR]

Abstract: Planar perovskite solar cells obtained by low‐temperature solution processing are of great promise, given a high compatibility with flexible substrates and perovskite‐based tandem devices, whilst benefitting from relatively simple manufacturing methods. However, ionic defects at surfaces usually cause detrimental carrier recombination, which links to one of dominant losses in device performance, slow transient responses, and notorious hysteresis. Here, it is shown that several different types of ionic defects can be simultaneously passivated by simple inorganic binary alkaline halide salts with their cations and anions. Compared to previous literature reports, this work demonstrates a promising passivation technology for perovskite solar cells. The efficient defect passivation significantly suppresses the recombination at the SnO2/perovskite interface, contributing to an increase in the open‐circuit voltage, the fast response of steady‐state efficiency, and the elimination of hysteresis. By this strong leveraging of multiple‐element passivation, low‐temperature‐processed, planar‐structured perovskite solar cells of 20.5% efficiencies, having negligible hysteresis, are obtained. Moreover, this defect‐passivation enhances the stability of solar cells with efficiency beyond 20%, retaining 90% of their initial performance after 30 d. This approach aims at developing the concept of defect engineering, which can be expanded to multiple‐element passivation from monoelement counterparts using simple and low‐cost inorganic materials. [ABSTRACT FROM AUTHOR]

Abstract: The thin‐film photovoltaic material Cu2ZnSnS4 (CZTS) has drawn worldwide attention in recent years due to its earth‐abundant, nontoxic element constitution, and remarkable photovoltaic performance. Although state‐of‐the‐art power conversion efficiency is achieved by hydrazine‐based methods, effort to fabricate such devices in a high throughput, environmental‐friendly way is still highlydesired. Here a hydrazine‐free all‐solution‐processed CZTS solar cell with Na2S self‐depleted back contact modification layer for the first time is demonstrated, using a ball‐milled CZTS as light absorber, low‐temperature solution‐processed ZnO electron‐transport layer as well as silver‐nanowire transparent electrode. The inserting of Na2S self‐depleted layer is proven to effectively stabilize the CZTS/Mo interface by eliminating a detrimental phase segregation reaction between CZTS and Mo‐coated soda lime glass, thus leading to a better crystallinity of CZTS light absorbing layer, enhanced carrier transportation at CZTS/Mo interface as well as a smaller series resistance. Furthermore, the self‐depletion feature of the Na2S modification layer also averts hole‐transportation barrier within the devices. The results show the vital importance of interfacial engineering for these CZST devices and the Na2S interface layer can be extended to other optoelectronic devices using Mo contact. [ABSTRACT FROM AUTHOR]

Sulfurization with various atmosphere and postheat treatments has been reported for earth abundant kesterite Cu2ZnSnS4 (CZTS) preparation as cost-effective material for next-generation solar cells. A full understanding of the nanoscale microstructure and chemistry of CZTS/CdS interface obtained from these different fabrication routes is currently lacking, yet is critical to developing optimal processing routes for high-performance kesterite solar cells. Here, the first detailed investigation of the interfacial microstructure and chemistry of CdS/Cu2ZnSnS4 heterojunctions is presented. For CZTS obtained from sulfurization in a sulfur-only atmosphere where highly defective surfaces are present, air annealing followed by etching in the initial stage of chemical bath deposition (CBD) process can effectively eliminate interfacial defects and allow the epitaxial growth of CBD-CdS, improving the minority lifetime, open circuit voltage ( VOC), and fill factor (FF) of the devices, while blocking Cd diffusion and deteriorating short circuit current ( Jsc). For CZTS from sulfurization in a combined sulfur and SnS atmosphere where CBD-CdS can directly epitaxially grow on CZTS and Cd-diffusion is clearly observed, associated devices show the longest lifetime and the highest efficiency of 8.76%. Epitaxial growth of CdS and Cd diffusion into CZTS are found to be two crucial features minimizing interfacial recombination and achieving high-efficiency devices. This will not only enhance the understanding of the device structure and physics of kesterite based solar cells, but also provide an effective way for designing other chalcogenide heterojunction solar cells. [ABSTRACT FROM AUTHOR]

A kesterite Cu2ZnSnS4 thin film solar cell with efficiency of over 9% is obtained by utilizing Zn1–xCdxS film as a replacement to traditional CdS buffer layer. Zn1–xCdxS film can optimize the conduction band offset between Cu2ZnSnS4 absorber and buffer, forming a minor positive conduction band alignment, thereby alleviating the recombination significantly and improving the open circuit voltage and fill factor efficiently. [ABSTRACT FROM AUTHOR]

Kesterite-based solar cells are attracting considerable attention in recent years, owing to the reduced toxicity and greater abundance of their constituent elements. In this brief review, we discuss the current status of this important technology by focusing on three key aspects of the device: (i) the interface between the kesterite absorber and the Mo back contact, (ii) the kesterite absorber bulk defects and grain boundaries and (iii) the interface between the kesterite absorber and the buffer layer. By identifying key issues to be addressed, we provide suggestions for their potential improvement and future research. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Various characterization methods are implemented to investigate the fundamental properties of a Cu2ZnSnS4 (CZTS) solar cell. The chemical distribution across the CZTS grain boundaries, the surface potential of CZTS absorber, the minority lifetime, the carrier collection length, diode ideality factor, dark saturation current, and series resistance are revealed in the characterization measurement. The short minority lifetime, high defect density, and large series resistance are confirmed and need to be addressed in the future work for further efficiency improvement. [ABSTRACT FROM AUTHOR]

The influence of three kinds of precursor depositions on the performance of corresponding CuZnSnS solar cells has been investigated, which includes evaporation of stacking metal layers (Mo/Zn/Cu/Sn), co-evaporation of metal elements (Mo/(Zn,Cu,Sn)) and co-evaporation of metals together with a small amount of sulfur (Mo/(Zn,Cu,Sn,S)) . It is found that Mo/(Zn,Cu,Sn) leads to large grain absorber and the best open circuit voltage V, short circuit current density J and efficiency; Mo/Zn/Cu/Sn produces a porous structure with small grain size which causes lowest shunt resistance, V, J and efficiency; Mo/(Zn,Cu,Sn,S) results in a dense film with small grain size which induces highest shunt resistance (R) and fill factor (FF); ~200 nm thick MoS layer is formed during the sulfurization. [ABSTRACT FROM AUTHOR]

A 20 nm Ag coating on Mo back contact was adopted to improve the back contact of evaporated Cu2ZnSnS4 (CZTS) solar cells. The Ag layer helped reduce the thickness of MoS2 which improves fill factor (FF) significantly; additionally, it reduced secondary phases ZnS and SnS2−x, which may help carrier transport; it was also involved in the doping of the absorber layer, which compensated the intrinsic p-type doping and therefore drags down the doping level. The doping involvement may enlarge the depletion region and improve lifetime of the absorber, which led to enhancing open circuit voltage (VOC), short circuit current density (JSC), and efficiency significantly. However, it degrades the crystallinity of the material slightly. [ABSTRACT FROM AUTHOR]

The effects of an ultrathin ZnO intermediate layer deposited at the CZTS/Mo interface on CZTS solar cell performance have been investigated in this work. The ZnO layer inhibits the generation of MoS2 layer and the formation of voids in the CZTS absorber. Consequently, the incorporation of this layer reduces the series resistance and increases the shunt resistance, which boosts photovoltaic conversion efficiency from 1.13% to 4.3%. (© 2014 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

an important step towards the realisation of silicon-based tandem solar cells using silicon quantum dots embedded in a silicon dioxide (SiO) matrix, single-junction silicon quantum dot (Si QD) solar cells on quartz substrates have been fabricated. The total thickness of the solar cell material is 420 nm. The cells contain 4 nm diameter Si quantum dots. The impacts of post-metallisation treatments such as phosphoric acid (HPO) etching, nitrogen (N) gas anneal and forming gas (Ar: H) anneal on the cells' electrical and photovoltaic properties are investigated. The Si QD solar cells studied in this work have achieved an open circuit voltage of 410 mV after various processes. Parameters extracted from dark I- V, light I- V and circular transfer length measurement (CTLM) suggest limiting mechanism in the Si QD solar cell operation and possible approaches for further improvement. [ABSTRACT FROM AUTHOR]

Antimony sulfide (Sb2S3) as a wide‐bandgap, nontoxic, and stable photovoltaic material reveals great potential for the uppermost cells in Si‐based tandem cell stacks. Sb2S3 solar cells with a compatible process, acceptable cost, and high efficiency therefore become the mandatory prerequisites to match silicon bottom cells. The performance of vacuum processed Sb2S3 device is pinned by bulk and interfacial recombination. Herein, a thermally treated TiO2 buffer layer induces quasiepitaxial growth of vertical orientation Sb2S3 absorber overcoming interface defects and absorber transport loss. Such novel growth could pronouncedly improve the open‐circuit voltage (Voc) due to the superior interface quality and intraribbon transport. The epitaxial rough Sb2S3 surface shows a texturized‐like morphology. It is optimized by tuning the grain sizes to form strong light trapping effect, which further enhances the short‐circuit current density (Jsc) with a 16% improvement. The final optimal device with high stability obtains a power conversion efficiency of 5.4%, which is the best efficiency for full‐inorganic Sb2S3 solar cells. The present developed quasiepitaxy strategy supports a superior interface, vertical orientation, and surface light trapping effect, which provides a new perspective for efficient noncubic material thin film solar cells. [ABSTRACT FROM AUTHOR]

While interfacial and grain‐boundary passivation presently attract enormous research interest for perovskite solar cells (PSCs), the improvement of Cs‐(FAPbI3)X(MAPbBr3)Y bulk quality still lacks systematical study, especially for constructing polycrystalline layers in planar configurations. Here, a DMSO‐molecule‐process for improving the quality of Cs‐(FAPbI3)0.85(MAPbBr3)0.15 is developed, where the molar ratio of precursors, the kind of anti‐solvents, and speed‐time profiles are found critical. The optimized treatment significantly enhanced the crystal orientation, grain size, surface roughness, photo‐response, carrier lifetime, and contact potential difference of absorbers. Cs‐(FAPbI3)0.85(MAPbBr3)0.15 absorbers also present superior charge transport, as well as reduced carrier recombination and decreased trap densities via DMSO‐molecule‐control, enabling performance improvement on both long‐term stability and photovoltaic parameters of 1 cm2 PSCs. Champion planar cells demonstrated a power conversion efficiency (PCE) of 21.07% (0.159 cm2) and PCE of 19.4% (1 cm2) with negligible hysteresis. Moreover, 1 cm2 devices retained 90% of initial PCE after aging 50 days in ambient air. DMSO‐molecule‐control is demonstrated to enhance the morphological and electronic qualities of Cs‐(FAPbI3)0.85(MAPbBr3)0.15 absorbers, thus increasing the efficiency (reaching 19.4%) and boosting the long‐term stability (retaining 90% of the initial efficiency after 50 days in ambient air) of 1 cm2 sized planar perovskite solar cells. [ABSTRACT FROM AUTHOR]

Understanding the elemental composition and point defect properties is crucial for improving device performance in Chalcogenide thin film solar cells. The correlation between composition and defect characteristics of CuSbS 2 thin film sulfurized from metallic precursors was systematically investigated. Interestingly, it was found that CuSbS 2 polycrystalline thin film maintains an overall Cu-rich composition with a Cu/Sb ratio greater than 1, regardless of the initial precursor compositions. Besides, no obvious difference in the performance of integrated devices is observed, due to the similar Cu/Sb atomic ratios and electronic properties (carrier concentration and mobility) in these CuSbS 2 thin films. By conducting admittance spectroscopy analysis on CuSbS 2 devices, identical defect energy was obtained at 280 meV above the valence band maximum, which can be ascribed to Cu Sb. This could be mainly explained by the Cu-rich composition induced low formation energy of Cu Sb. Therefore, further defects engineering focusing on Cu Sb is required to boost the device efficiency of CuSbS 2 solar cells. • The correlation between composition and defect characteristics has been systematically studied in CuSbS 2 solar cells. • Polycrystalline CuSbS 2 thin-films exhibit a Cu-rich composition across a wide range of initial precursor compositions. • Polycrystalline CuSbS 2 shows consistent Cu/Sb ratios and electronic properties, regardless of precursor compositions. • Cu Sb is revealed to be the dominant defect in Cu-rich CuSbS 2 thin-film prepared by the co-sputtering method. [ABSTRACT FROM AUTHOR]

Abstract: Properties of heavily boron-doped hydrogenated polycrystalline germanium (Ge) films sputter-deposited on glass are investigated for developing p+ emitters of the bottom cells of low cost monolithic tandem solar cells. The films were deposited and in-situ doped by co-sputtering Ge with boron at various power levels (P B) in a mixture of argon and hydrogen at 500°C, and then followed by a rapid thermal anneal process at 550°C for 120s or 600°C for 60s, respectively. The dependence of the structural properties of the films on the various boron incorporations as well as annealing conditions was explored by Raman and X-ray diffraction measurements. We find that the films as deposited at 500°C are polycrystalline with strong (220) preferential orientation, which are normally of columnar structure, confirmed by cross-sectional transmission electron microscopy. Revealed by Hall measurements, a boron activation level of 6.24×1019 atoms/cm3, well above reported maximum solid solubility in crystalline Ge, was obtained in the as deposited film at P B=55W. Annealing at 600°C enhanced the concentration to 1.21×1020 atoms/cm3. A fact that boron hardly diffuses in Ge at temperatures below 800°C makes the resultant material an excellent candidate for thin p+ emitters of the bottom cells of monolithic tandem solar cells. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogenated polycrystalline Si x Ge1−x films, with a varying silicon fraction x ≤0.246, were in situ deposited in an argon and hydrogen mixture at 500°C using radio frequency sputtering with an aim to develop a material for the bottom cell of a low cost monolithic tandem solar cell. Silicon and germanium atomic compositions of the films were determined by X-ray photoelectron spectroscopy (XPS). Structural evolution revealed by Raman and X-ray diffraction (XRD) indicated that the crystallinity of the films was improved with decreasing silicon fraction, accompanied with an increase of surface roughness verified by atomic force microscopy (AFM). Optical band gaps of these films derived from Tauc plots, which were calculated from reflectance/transmittance measurements, decreased with decreasing silicon fraction. Resistivity of the films, determined by four-point-probe technique, significantly decreased as well. High quality with low thermal budget obtained in this work suggests the films could be used in thin film solar cells on glass. [ABSTRACT FROM AUTHOR]

Sb 2 S 3 and CuSbS 2 have been proposed as alternative earth-abundant absorber materials for thin-film solar cells. However, no thermodynamic study of the S−Sb binary system and the Cu−S−Sb ternary system were investigated. In this paper, The S−Sb system and the Cu−S−Sb system are calculated utilizing the so-called CALPHAD (CALculation of PHAse Diagrams) technique. Using TEM-EDS and XRD, Cu 0.9 Sb 1 S 2 is experimentally confirmed at the Cu 1 Sb 1 S 2 and Sb 2 S 3 two-phases region in the isothermal section at 673 K of the Cu−S−Sb ternary system. Given the asymmetric shape and miscibility gap of the liquidus in the S−Sb phase diagram, the associate solution model for the liquid phase is adopted. The solution phases (liquid, bcc, fcc) are treated with the Redlich–Kister equation. The compounds S 3 Sb 2 , Cu 3 SbS 3 , Cu 12 Sb 4 S 13 , CuSbS 2 , and Cu 3 SbS 4 are described as a stoichiometric compound. A set of self-consistent thermodynamic parameters of the S−Sb binary system and the Cu−S−Sb ternary system are obtained. The calculated results are in good agreement with the experimental data. This study provides a set of reliable thermodynamic parameters to the Cu−Sb−S thermodynamic database, and a cost-effective tool to design material synthesis experiments and manufacturing processes. [ABSTRACT FROM AUTHOR]

• Preparation of CZTS thin films via facile and environmentally friendly SILAR method. • Analysis of the effects of different annealing temperature and holding time on film quality. • Fabrication of 4.26% efficiency solar cells by water-based inorganic method. Kesterite Cu 2 ZnSnS 4 (CZTS) solar cells are regarded as a promising photovoltaic technology owing to the non-toxic and earth-abundant constitutes. With the application of scalable and low-cost solution methods, the possibility of its commercialization can be further increased. This work explores preparing prominent CZTS films by an economically feasible successive ionic adsorption and reaction (SILAR) synthesis method. The obtained precursor with the Mo/ZnS/Cu 2 SnS 3 structure requires appropriate substantial annealing under a chalcogen atmosphere to form kesterite CZTS films. The annealing process is therefore optimized to improve the film quality and the performance of solar cells. Specifically, the optimal annealing condition is determined by adjusting the annealing temperature and holding time, respectively. The CZTS film annealed at 580 °C for 60 min demonstrates better film quality in terms of surface morphology, crystallinity, and phase purity. Consequently, CZTS solar cells fabricated with the optimal absorber exhibit a preferable efficiency of up to 4.26%. [ABSTRACT FROM AUTHOR]

This review summarizes some emerging inorganic photovoltaic materials including Cu(In,Ga)Se 2 (CIGSe), kesterite Cu 2 ZnSn(S,Se) 4 (CZTSSe), CdTe, Sb 2 Se 3 and inorganic perovskite CsPb(I 1− x Br x) 3. The materials features, development history and performance enhancements for each of solar cells are discussed in detail. The efficient conversion of solar energy to electricity for human utilization heavily relies on the development of solar cells. Nowadays, a variety of high-performance solar cells are constantly emerging. Thin-film solar cells made from inorganic materials have constituted one of the major categories of solar cells showing potential in the fast growing photovoltaic (PV) market. In order to provide an overall grasp of and insight into the future direction of inorganic thin-film solar cell development, we review key emerging and representative inorganic photovoltaic materials including chalcopyrite Cu(In,Ga)Se 2 (CIGSe), kesterite Cu 2 ZnSn(S,Se) 4 (CZTSSe), CdTe, Sb 2 Se 3 and inorganic perovskite CsPb(I 1− x Br x) 3 in this paper. Absorber materials, evolution of device development, and current challenges and key strategies for performance enhancement are detailed. [ABSTRACT FROM AUTHOR]

Among various thin-film solar cell absorber materials, the kesterite semiconductor Cu SB 2 sb ZnSn(S, Se) SB 4 sb (CZTSSe) is composed of earth-abundant and environmental-friendly elements while possessing promising optical-electrical properties. This leads to a short minority carrier lifetime and diffusion length in CZTSSe solar cells, which is almost one order of magnitude lower than that in CdTe, CIGSe and perovskite, let alone silicon solar cells. However, the low critical temperature of Cu and Zn position replacement in CZTSSe implies that the influence of the significant amount of Cu-Zn disorder cannot be eliminated during the study of other defects/defect clusters. Massive Cu-Zn antisite defects in the bulk of CZTSSe result from nearly the same cation sizes as well as small chemical mismatch of Cu SP + sp and Zn SP + sp . [Extracted from the article]

Cadmium sulfide (CdS) is the most widely used buffer material for a variety of thin-film solar cells including Cu 2 ZnSnS 4 . However, reports have shown that CdS film obtained by chemical bath deposition (CBD) is not the ideal buffer layer for pure sulfide CZTS solar cell. Zinc doping is a viable approach to modifying the CdS buffer film, but the present methods are far from satisfactory. Here, we innovatively developed an effective way of Zinc doping using partial electrolyte (PE) treatment, resulting in state-of-the-art buffer layer for solar cells based on high-surface-waviness CZTS light absorber. Our study shows that this Zn PE-treated CdS film improved the properties including coverage, full-range light transmittance and conduction band alignment with CZTS. Ultimately, the resultant modified CdS film boosted the open-circuit voltage of our devices by more than 100 mV, yielding power conversion efficiency (PCE) of 3.30%. We note that this is the highest efficiency that has been reported for all solution-processed CZTS solar cells. [ABSTRACT FROM AUTHOR]

A hole-transporting layer is essential for effective operation of planar perovskite solar cells. Hole-transporting materials (HTMs) used so far are mainly based on organic semiconductors, which are usually expensive and relatively instable compared with inorganic materials. In this article, crystalline selenium (c-Se) prepared by thermal evaporation followed by annealing at low temperature was used as the hole-transporting layer for the planar perovskite solar cells in the device structure of fluorine-doped tin oxide (FTO)/SnO 2 /perovskite/selenium/Au. The device employing c-Se as HTM displayed enhanced long-term stability, keeping 80% of the original efficiency after 40 days in ambient environment. However, the power conversion efficiency of 8.3% remains low compared with the device based on spiroOMeTAD, which results from higher recombination in the c-Se device as determined by impedance spectroscopy. Thermal-evaporated selenium could be a low-cost and easy-fabrication HTM for efficient and stable perovskite solar cells after reducing the recombination in devices. [ABSTRACT FROM AUTHOR]