Heterojunction Annealing Enabling Record Open-Circuit Voltage in Antimony Triselenide Solar Cells

Active Passivation of Anion Vacancies in Antimony Selenide Film for Efficient Solar Cells

Binary antimony selenide (Sb2Se3) is a promising inorganic light-harvesting material with high stability, nontoxicity, and wide light harvesting capability. In this photovoltaic material, it has been recognized that deep energy level defects with large carrier capture cross section, such as VSe (selenium vacancy), lead to serious open-circuit voltage (VOC) deficit and in turn limit the achievable power conversion efficiency (PCE) of Sb2Se3 solar cells. Understanding the nature of deep-level defects and establishing effective method to eliminate the defects are vital to improving VOC. In this study, a novel directed defect passivation strategy is proposed to suppress the formation of VSe and maintain the composition and morphology of Sb2Se3 film. In particular, through systematic study on the evolution of defect properties, the pathway of defect passivation reaction is revealed. Owing to the inhibition of defect-assisted recombination, the VOC increases, resulting in an improvement of PCE from 7.69% to 8.90%, which is the highest efficiency of Sb2Se3 solar cells prepared by thermal evaporation method with superstrate device configuration. This study proposes a new understanding of the nature of deep-level defects and enlightens the fabrication of high quality Sb2Se3 thin film for solar cell applications.

Effective Non-Radiative Interfacial Recombination Suppression Scenario Using Air Annealing for Antimony Triselenide Thin-Film Solar Cells

Antimony triselenide (Sb2Se3) has become a very promising candidate for next-generation thin-film solar cells due to the merits of their low-cost, low-toxic and excellent optoelectronic properties. Despite Sb2Se3 thin-film photovoltaic technology having undergone rapid development over the past few years, insufficient doping concentration and severe recombination have been the most challenging limitations hindering further breakthroughs for the Sb2Se3 solar cells. Post-annealing treatment of the Sb2Se3/CdS heterojunction was demonstrated to be very helpful in improving the device performance previously. In this work, post-annealing treatments were applied to the Sb2Se3/CdS heterojunction under a vacuum and in the air, respectively. It was found that compared to the vacuum annealing scenario, the air-annealed device presented notable enhancements in open-circuit voltage. Ultimately a competitive power conversion efficiency of 7.62% was achieved for the champion device via air annealing. Key photovoltaic parameters of the Sb2Se3 solar cells were measured and the effects of post-annealing treatments using different scenarios on the devices were discussed.

Back Interface and Absorber Bulk Deep-Level Trap Optimization Enables Highly Efficient Flexible Antimony Triselenide Solar Cell

The unique 1D crystal structure of Antimony Triselenide (Sb2Se3) offers notable potential for use in flexible, lightweight devices due to its excellent bending characteristics. However, fabricating high-efficiency flexible Sb2Se3 solar cells is challenging, primarily due to the suboptimal contact interface between the embedded Sb2Se3 layer and the molybdenum back-contact, compounded by complex intrinsic defects. This study introduces a novel Molybdenum Trioxide (MoO3) interlayer to address the back contact interface issues in flexible Sb2Se3 devices. Further investigations indicate that incorporating a MoO3 interlayer not only enhances the crystalline quality but also promotes a favorable [hk1] growth orientation in the Sb2Se3 absorber layer. It also reduces the barrier height at the back contact interface and effectively passivates harmful defects. As a result, the flexible Sb2Se3 solar cell, featuring a Mo-foil/Mo/MoO3/Sb2Se3/CdS/ITO/Ag substrate structure, demonstrates exceptional flexibility and durability, enduring large bending radii and multiple bending cycles while achieving an impressive efficiency of 8.23%. This research offers a straightforward approach to enhancing the performance of flexible Sb2Se3 devices, thereby expanding their application scope in the field of photovoltaics.

In-Sb Covalent Bonds over Sb2Se3/In2Se3 Heterojunction for Enhanced Photoelectrochemical Water Splitting

Antimony selenide is a promising P-type photocatalyst, but it has a large number of deep energy level defects, leading to severe carrier recombination. The construction of a heterojunction is a common way to resolve this problem. However, the conventional heterojunction system inevitably introduces interface defects. Herein, we employ in situ synthesis to epitaxially grow In2Se3 nanosheets on Sb2Se3 nanorods and form In-Sb covalent interfacial bonds. This petal-shaped heterostructure reduced interface defects and enhanced the efficiency of carrier separation and transport. In this work, the photocurrent density in the proposed Sb2Se3/In2Se3 photocathode is 0.485 mA cm-2 at 0 VRHE, which is 30 times higher than that of pristine Sb2Se3 and it has prominent long-term stability for 24 h without obvious decay. The results reveal that the synergy of the bidirectional built-in electric field constructed between In2Se3 and Sb2Se3 and the solid In-Sb interfacial bonds together build a high-efficiency transport channel for the photogenerated carriers that display enhanced photoelectrochemical (PEC) water-splitting performance. This work provides efficient guidance for reducing interface defects via the in situ synthesis and construction of interfacial bonds.

Controlled Epitaxial Growth of (hk1)-Sb2Se3 Film on Cu9S5 Single Crystal via Post-Annealing Treatment for Photodetection Application

Antimony selenide (Sb2Se3) is a promising semiconductor for photodetector applications due to its unique photovoltaic properties. Achieving optimal carrier transport in (001)-Sb2Se3 by the material of contacting substrate requires in-depth study. In this paper, the induced growth of Sb2Se3 films from (hk0) to (hk1) planes is achieved on digenite (Cu9S5) films by post-annealing treatment. The flake-like and flower-like morphologies on the surface of Sb2Se3 films are caused by different thicknesses of the Cu9S5 films, which are related to the (hk0) and (hk1) planes of Sb2Se3 surface. The epitaxial growth of Sb2Se3 films on (105)-Cu9S5 surfaces exhibits thickness dependence. The results inform research into the controlled induced growth of low-dimensional materials. The device of Sb2Se3/Cu9S5/Si has good broadband response (visible to near-infrared), self-powered characteristics, and stability. As the crystalline quality of the Sb2Se3 film increases along the (hk1) plane, the carrier transport is enhanced correspondingly. Under the 980 nm light irradiation, the device has an excellent switching ratio of 2 × 104 at 0 bias, with responsivity, detectivity, and response time up to 17 µA W-1, 1.48 × 107 Jones, and 355/490 µs, respectively. This suggests that Sb2Se3 is suitable for self-powered photodetectors and related optical and optoelectronic devices.

Promoting effect of lanthanum doping on photovoltaic performance of CZTSSe solar cells

A large open-circuit voltage (VOC) deficit is the major challenge hindering the efficiency improvement of Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. Cation substitution, or doping, is usually an effective strategy to achieve carrier regulation and improve efficiency. In this work, we developed a rare-earth element lanthanum (La) doped CZTSSe thin-film solar cell by directly introducing La3+ ions into the CZTS precursor solution. Such a proposed La doping approach could effectively enhance light harvesting, adjust the bandgap, and increase the electron diffusion length. Furthermore, appropriate concentrations of La doping can reduce harmful defect cluster. Benefiting from the La doping, the VOC significantly increases from 431 to 497 mV. Consequently, the power conversion efficiency is enhanced significantly from 6.54% (VOC = 431 mV, JSC = 25.50 mA/cm2, FF = 58.28%) for the reference cell to 10.21% (VOC = 497 mV, JSC = 35.20 mA/cm2, FF = 58.41%) for the optimized La-doped cell. This research provides a new direction for enhancing the performance of CZTSSe cells, offering promising prospects for the future of CZTSSe thin-film solar cells.

Suppressing Deep-Level Trap Toward Over 13% Efficient Solution-Processed Kesterite Solar Cell

Cu2ZnSn (S,Se)4 (CZTSSe), a promising absorption material for thin-film solar cells, still falls short of reaching the balance limit efficiency due to the presence of various defects and high defect concentration in the thin film. During the high-temperature selenization process of CZTSSe, the diffusion of various elements and chemical reactions significantly influence defect formation. In this study, a NaOH-Se intermediate layer introduced at the back interface can optimize Cu2ZnSnS4 (CZTS)precursor films and subsequently adjust the Se and alkali metal content to favor grain growth during selenization. Through this back interface engineering, issues such as non-uniform grain arrangement on the surface, voids in bulk regions, and poor contact at the back interface of absorber layers are effectively addressed. This method not only optimizes morphology but also suppresses deep-level defect formation, thereby promoting carrier transport at both interfaces and bulk regions of the absorber layer. Consequently, CZTSSe devices with a NaOH-Se intermediate layer improved fill factor, open-circuit voltage, and efficiency by 13.3%. This work initiates from precursor thin films via back interface engineering to fabricate high-quality absorber layers while advancing the understanding regarding the role played by intermediate layers at the back interface of kesterite solar cells.

Designing Atomic Interface in Sb2 S3 /CdS Heterojunction for Efficient Solar Water Splitting

In the emerging Sb2 S3 -based solar energy conversion devices, a CdS buffer layer prepared by chemical bath deposition is commonly used to improve the separation of photogenerated electron-hole pairs. However, the cation diffusion at the Sb2 S3 /CdS interface induces detrimental defects but is often overlooked. Designing a stable interface in the Sb2 S3 /CdS heterojunction is essential to achieve high solar energy conversion efficiency. As a proof of concept, this study reports that the modification of the Sb2 S3 /CdS heterojunction with an ultrathin Al2 O3 interlayer effectively suppresses the interfacial defects by preventing the diffusion of Cd2+ cations into the Sb2 S3 layer. As a result, a water-splitting photocathode based on Ag:Sb2 S3 /Al2 O3 /CdS heterojunction achieves a significantly improved half-cell solar-to-hydrogen efficiency of 2.78% in a neutral electrolyte, as compared to 1.66% for the control Ag:Sb2 S3 /CdS device. This work demonstrates the importance of designing atomic interfaces and may provide a guideline for the fabrication of high-performance stibnite-type semiconductor-based solar energy conversion devices.

(Bi,Sb)2 Se3 Alloy Thin Film for Short-Wavelength Infrared Photodetector and TFT Monolithic-Integrated Matrix Imaging

Short-wavelength infrared photodetectors play a significant role in various fields such as autonomous driving, military security, and biological medicine. However, state-of-the-art short-wavelength infrared photodetectors, such as InGaAs, require high-temperature fabrication and heterogenous integration with complementary metal-oxide-semiconductor (CMOS) readout circuits (ROIC), resulting in a high cost and low imaging resolution. Herein, for the first time, a low-cost, high-performance, high-stable, and thin-film transistor (TFT) ROIC monolithic-integrated (Bi,Sb)2 Se3 alloy thin-film short-wavelength infrared photodetector is reported. The (Bi,Sb)2 Se3 alloy thin-film short-wavelength infrared photodetectors demonstrate a high external quantum efficiency (EQE) of 21.1% (light intensity of 0.76 µW cm-2 ) and a fast response time (3.24 µs). The highest EQE is about two magnitudes than that of the extrinsic photoconduction of Sb2 Se3 (0.051%). In addition, the unpackaged devices demonstrate high electric and thermal stability (almost no attenuation at 120 °C for 312 h), showing potential for in-vehicle applications that may experient such a high temperature. Finally, both the (Bi,Sb)2 Se3 alloy thin film and n-type CdSe buffer layer are directly deposited on the TFT ROIC (with a 64 × 64-pixel array) with a low-temperature process and the material identification and imaging applications are presented. This work is a significant breakthrough in ROIC monolithic-integrated short-wavelength infrared imaging chips.

Suppressing Buried Interface Nonradiative Recombination Losses Toward High-Efficiency Antimony Triselenide Solar Cells

Antimony triselenide (Sb2 Se3 ) has possessed excellent optoelectronic properties and has gained interest as a light-harvesting material for photovoltaic technology over the past several years. However, the severe interfacial and bulk recombination obviously contribute to significant carrier transport loss thus leading to the deterioration of power conversion efficiency (PCE). In this work, buried interface and heterojunction engineering are synergistically employed to regulate the film growth kinetic and optimize the band alignment. Through this approach, the orientation of the precursor films is successfully controlled, promoting the preferred orientational growth of the (hk1) of the Sb2 Se3 films. Besides, interfacial trap-assisted nonradiative recombination loss and heterojunction band alignment are successfully minimized and optimized. As a result, the champion device presents a PCE of 9.24% with short-circuit density (JSC ) and fill factor (FF) of 29.47 mA cm-2 and 63.65%, respectively, representing the highest efficiency in sputtered-derived Sb2 Se3 solar cells. This work provides an insightful prescription for fabricating high-quality Sb2 Se3 thin film and enhancing the performance of Sb2 Se3 solar cells.

Grain Engineering of Sb2 S3 Thin Films to Enable Efficient Planar Solar Cells with High Open-Circuit Voltage

Sb2 S3 is a promising environmentally friendly semiconductor for high performance solar cells. But, like many other polycrystalline materials, Sb2 S3 is limited by nonradiative recombination and carrier scattering by grain boundaries (GBs). This work shows how the GB density in Sb2 S3 films can be significantly reduced from 1068 ± 40 to 327 ± 23 nm µm-2 by incorporating an appropriate amount of Ce3+ into the precursor solution for Sb2 S3 deposition. Through extensive characterization of structural, morphological, and optoelectronic properties, complemented with computations, it is revealed that a critical factor is the formation of an ultrathin Ce2 S3 layer at the CdS/Sb2 S3 interface, which can reduce the interfacial energy and increase the adhesion work between Sb2 S3 and the substrate to encourage heterogeneous nucleation of Sb2 S3 , as well as promote lateral grain growth. Through reductions in nonradiative recombination at GBs and/or the CdS/Sb2 S3 heterointerface, as well as improved charge-carrier transport properties at the heterojunction, this work achieves high performance Sb2 S3 solar cells with a power conversion efficiency reaching 7.66%. An impressive open-circuit voltage (VOC ) of 796 mV is achieved, which is the highest reported thus far for Sb2 S3 solar cells. This work provides a strategy to simultaneously regulate the nucleation and growth of Sb2 S3 absorber films for enhanced device performance.

Electron Transport Layer Engineering Induced Carrier Dynamics Optimization for Efficient Cd-Free Sb2 Se3 Thin-Film Solar Cells

Antimony selenide (Sb2 Se3 ) is a highly promising photovoltaic material thanks to its outstanding optoelectronic properties, as well as its cost-effective and eco-friendly merits. However, toxic CdS is widely used as an electron transport layer (ETL) in efficient Sb2 Se3 solar cells, which largely limit their development toward market commercialization. Herein, an effective green Cd-free ETL of SnOx is introduced and deposited by atomic layer deposition method. Additionally, an important post-annealing treatment is designed to further optimize the functional layers and the heterojunction interface properties. Such engineering strategy can optimize SnOx ETL with higher nano-crystallinity, higher carrier density, and less defect groups, modify Sb2 Se3 /SnOx heterojunction with better interface performance and much desirable "spike-like" band alignment, and also improve the Sb2 Se3 light absorber layer quality with passivated bulk defects and prolonged carrier lifetime, and therefore to enhance carrier separation and transport while suppressing non-radiative recombination. Finally, the as-fabricated Cd-free Mo/Sb2 Se3 /SnOx /ITO/Ag thin-film solar cell exhibits a stimulating efficiency of 7.39%, contributing a record value for Cd-free substrate structured Sb2 Se3 solar cells reported to date. This work provides a viable strategy for developing and broadening practical applications of environmental-friendly Sb2 Se3 photovoltaic devices.

Enhancement in the Efficiency of Sb2 Se3 Solar Cells by Triple Function of Lithium Hydroxide Modified at the Back Contact Interface

The efficiency of antimony selenide (Sb2 Se3 ) solar cells is still limited by significant interface and deep-level defects, in addition to carrier recombination at the back contact surface. This paper investigates the use of lithium (Li) ions as dopant for Sb2 Se3 films, using lithium hydroxide (LiOH) as a dopant medium. Surprisingly, the LiOH solution not only reacts at the back surface of the Sb2 Se3 film but also penetrate inside the film along the (Sb4 Se6 )n molecular chain. First, the Li ions modify the grain boundary's carrier type and create an electric field between p-type grain interiors and n-type grain boundary. Second, a gradient band structure is formed along the vertical direction with the diffusion of Li ions. Third, carrier collection and transport are improved at the surface between Sb2 Se3 and the Au layer due to the reaction between the film and alkaline solution. Additionally, the diffusion of Li ions increases the crystallinity, orientation, surface evenness, and optical electricity. Ultimately, the efficiency of Sb2 Se3 solar cells is improved to 7.57% due to the enhanced carrier extraction, transport, and collection, as well as the reduction of carrier recombination and deep defect density. This efficiency is also a record for CdS/Sb2 Se3 solar cells fabricated by rapid thermal evaporation.

Cadmium-Free Kesterite Thin-Film Solar Cells with High Efficiency Approaching 12

Cadmium sulfide (CdS) buffer layer is commonly used in Kesterite Cu2 ZnSn(S,Se)4 (CZTSSe) thin film solar cells. However, the toxicity of Cadmium (Cd) and perilous waste, which is generated during the deposition process (chemical bath deposition), and the narrow bandgap (≈2.4 eV) of CdS restrict its large-scale future application. Herein, the atomic layer deposition (ALD) method is proposed to deposit zinc-tin-oxide (ZTO) as a buffer layer in Ag-doped CZTSSe solar cells. It is found that the ZTO buffer layer improves the band alignment at the Ag-CZTSSe/ZTO heterojunction interface. The smaller contact potential difference of the ZTO facilitates the extraction of charge carriers and promotes carrier transport. The better p-n junction quality helps to improve the open-circuit voltage (VOC ) and fill factor (FF). Meanwhile, the wider bandgap of ZTO assists to transfer more photons to the CZTSSe absorber, and more photocarriers are generated thus improving short-circuit current density (Jsc). Ultimately, Ag-CZTSSe/ZTO device with 10 nm thick ZTO layer and 5:1 (Zn:Sn) ratio, Sn/(Sn + Zn): 0.28 deliver a superior power conversion efficiency (PCE) of 11.8%. As far as it is known that 11.8% is the highest efficiency among Cd-free kesterite thin film solar cells.

High-Performance and Stable Sb2S3 Thin-Film Photodetectors for Potential Application in Visible Light Communication

Photodetectors (PDs) are critical parts of visible light communication (VLC) systems for achieving efficient photoelectronic conversion and high-fidelity transmission of signals. Antimony sulfide (Sb₂S₃) as a nontoxic, high optical absorption coefficient, and low-cost semiconductor becomes a promising candidate for applications in VLC systems. Particularly, Sb₂S₃ PDs were verified to have significantly weak light detection ability in the visible region. However, the response speed of Sb₂S₃ PDs with existing device structures is still relatively slow. Herein, through optimizing the device structure for the p-i-n type PDs, a p-type Sb₂Se₃ hole transport layer (HTL) is designed to enhance the built-in electric field and to accelerate the migration of photogenerated carriers for the high responsivity and fast response speed. The optimal thickness of the structure is obtained through the simulation of SCAPS-1D software, and the optimized devices show high-performance parameters, including a responsivity of 0.34 A W^-1, a specific detectivity (D^*) of 2.20 × 10¹² Jones, the -3 dB bandwidth of 440 kHz, high stability, and the value of the Sb₂S₃ PDs can reach 60% in the range of 360-600 nm, which indicates that the device is very suitable for working in the visible light band. In addition, the resulting Sb₂S₃ PD is successfully integrated into VLC systems by designing a matched light detection circuit. The results suggest that the Sb₂S₃ PDs are expected to provide an alternative to future VLC system applications.

Vertically Aligned One-Dimensional Crystal-Structured Sb2Se3 for High-Efficiency Flexible Solar Cells via Regulating Selenization Kinetics

Recently, antimony selenide (Sb₂Se₃) has exhibited an exciting potential for flexible photoelectric applications due to its unique one-dimensional (1D) chain-type crystal structure, low-cost constituents, and superior optoelectronic properties. The 1D structure endows Sb₂Se₃ with a strong anisotropy in carrier transport and a lasting mechanical deformation tolerance. The control of the crystalline orientation of the Sb₂Se₃ film is an essential requirement for its device performance optimization. However, the current state-of-the-art Sb₂Se₃ devices suffer from unsatisfactory orientation control, especially for the (001) orientation, in which the chains stand vertically. Herein, we achieved an unprecedented control of the (001) orientation for the growth of the Sb₂Se₃ film on a flexible Mo-coated mica substrate by balancing the collision rate and kinetic energy of Se vapor particles with the surface of Sb film by regulating the selenization kinetics. Based on this (001)-oriented Sb₂Se₃ film, a high efficiency of 8.42% with a record open-circuit voltage (V_OC) of 0.47 V is obtained for flexible Sb₂Se₃ solar cells. The vertical van der Waals gaps in the (001) orientation provide favorable diffusion paths for Se atoms, which results in a Se-rich state at the bottom of the Sb₂Se₃ film and promotes the in situ formation of the MoSe₂ interlayer between Mo and Sb₂Se₃. These phenomena contribute to a back-surface field enhanced absorber layer and a quasi-Ohmic back contact, improving the device's V_OC and the collection of carriers. This method provides an effective strategy for the orientation control of 1D materials for efficient photoelectric devices.

Improved Carrier Lifetimes of CdSe Thin Film via Te Doping for Photovoltaic Application

Cadmium selenide (CdSe) solar cells have proven to be a remarkable potential top cell for a silicon-based tandem application. However, the defects and short carrier lifetimes of CdSe thin films greatly limit the solar cell performance. In this work, a Te-doped strategy is proposed to passivate the Se vacancy defects and increase the carrier lifetime of the CdSe thin film. The theoretical calculation helps to reveal the mechanism of nonradiative recombination of the CdSe thin film in depth. After Te-doping, the calculated capture coefficient of CdSe can be reduced from 4.61 × 10^-8 cm³ s^-1 to 2.32 × 10^-9 cm³ s^-1. Meanwhile, the carrier lifetime of CdSe thin film is increased nearly 3-fold from 0.53 to 1.43 ns. Finally, the efficiency of the Cd(Se,Te) solar cell is improved to 4.11%, about a relative 36.5% improvement compared to the pure CdSe solar cell. Both theoretical calculations and experiments prove that Te can effectively passivate bulk defects and improve the carrier lifetime of CdSe thin films, deserving further exploration to improve solar cell performance.

Tellurium Doping Inducing Defect Passivation for Highly Effective Antimony Selenide Thin Film Solar Cell

Antimony selenide (Sb₂Se₃) is emerging as a promising photovoltaic material owing to its excellent photoelectric property. However, the low carrier transport efficiency, and detrimental surface oxidation of the Sb₂Se₃ thin film greatly influenced the further improvement of the device efficiency. In this study, the introduction of tellurium (Te) can induce the benign growth orientation and the desirable Sb/Se atomic ratio in the Te-Sb₂Se₃ thin film. Under various characterizations, it found that the Te-doping tended to form Sb₂Te₃-doped Sb₂Se₃, instead of alloy-type Sb₂(Se,Te)₃. After Te doping, the mitigation of surface oxidation has been confirmed by the Raman spectra. High-quality Te-Sb₂Se₃ thin films with preferred [hk1] orientation, large grain size, and low defect density can be successfully prepared. Consequently, a 7.61% efficiency Sb₂Se₃ solar cell has been achieved with a V_OC of 474 mV, a J_SC of 25.88 mA/cm², and an FF of 64.09%. This work can provide an effective strategy for optimizing the physical properties of the Sb₂Se₃ absorber, and therefore the further efficiency improvement of the Sb₂Se₃ solar cells.

Energy Band Alignment by Solution-Processed Aluminum Doping Strategy toward Record Efficiency in Pulsed Laser-Deposited Kesterite Thin-Film Solar Cell

Kesterite-based Cu2ZnSnS4 (CZTS) thin-film photovoltaics involve a serious interfacial dilemma, leading to severe recombination of carriers and insufficient band alignment at the CZTS/CdS heterojunction. Herein, an interface modification scheme by aluminum doping is introduced for CZTS/CdS via a spin coating method combined with heat treatment. The thermal annealing of the kesterite/CdS junction drives the migration of doped Al from CdS to the absorber, achieving an effective ion substitution and interface passivation. This condition greatly reduces interface recombination and improves device fill factor and current density. The JSC and FF of the champion device increased from 18.01 to 22.33 mA cm-2 and 60.24 to 64.06%, respectively, owing to the optimized band alignment and remarkably enhanced charge carrier generation, separation, and transport. Consequently, a photoelectric conversion efficiency (PCE) of 8.65% was achieved, representing the highest efficiency in CZTS thin-film solar cells fabricated by pulsed laser deposition (PLD) to date. This work proposed a facile strategy for interfacial engineering treatment, opening a valuable avenue to overcome the efficiency bottleneck of CZTS thin-film solar cells.

Thermally Driven Point Defect Transformation in Antimony Selenosulfide Photovoltaic Materials

Thermal treatment of inorganic thin films is a general and necessary step to facilitate crystallization and, in particular, to regulate the formation of point defects. Understanding the dependence of the defect formation mechanism on the annealing process is a critical challenge in terms of designing material synthesis approaches for obtaining desired optoelectronic properties. Herein, a mechanistic understanding of the evolution of defects in emerging Sb₂ (S,Se)₃ solar cell films is presented. A top-efficiency Sb₂ (S,Se)₃ solar-cell film is adopted in this study to consolidate this investigation. This study reveals that, under hydrothermal conditions, the as-deposited Sb₂ (S,Se)₃ film generates defects with a high formation energy, demonstrating kinetically favorable defect formation characteristics. Annealing at elevated temperatures leads to a two-step defect transformation process: 1) formation of sulfur and selenium vacancy defects, followed by 2) migration of antimony ions to fill the vacancy defects. This process finally results in the generation of cation-anion antisite defects, which exhibit low formation energy, suggesting a thermodynamically favorable defect formation feature. This study establishes a new strategy for the fundamental investigation of the evolution of deep-level defects in metal chalcogenide films and provides guidance for designing material synthesis strategies in terms of defect control.

Oxygen Content Modulation Toward Highly Efficient Sb2Se3 Solar Cells

Vapor-transport deposition (VTD) method is the main technique for the preparation of Sb₂Se₃ films. However, oxygen is often present in the vacuum tube in such a vacuum deposition process, and Sb₂O₃ is formed on the surface of Sb₂Se₃ because the bonding of Sb-O is formed more easily than that of Sb-Se. In this work, the formation of Sb₂O₃ and thus the carrier transport in the corresponding solar cells were studied by tailoring the deposition microenvironment in the vacuum tube during Sb₂Se₃ film deposition. Combined by different characterization techniques, we found that tailoring the deposition microenvironment can not only effectively inhibit the formation of Sb₂O₃ at the CdS/Sb₂Se₃ interface but also enhance the crystalline quality of the Sb₂Se₃ thin film. In particular, such modification induces the formation of (hkl, l = 1)-oriented Sb₂Se₃ thin films, reducing the interface recombination of the subsequently fabricated devices. Finally, the Sb₂Se₃ solar cell with the configuration of ITO/CdS/Sb₂Se₃/Spiro-OMeTAD/Au achieves a champion efficiency of 7.27%, a high record for Sb₂Se₃ solar cells prepared by the VTD method. This work offers guidance for the preparation of high-efficiency Sb₂Se₃ thin-film solar cells under rough-vacuum conditions.

Exploring Cu-Doping for Performance Improvement in Sb2Se3 Photovoltaic Solar Cells

Copper-doped antimony selenide (Cu-doped Sb2Se3) thin films were deposited as absorber layers in photovoltaic solar cells using the low-temperature pulsed electron deposition (LT-PED) technique, starting from Sb2Se3 targets where part of the Sb was replaced with Cu. From a crystalline point of view, the best results were achieved for thin films with about Sb1.75Cu0.25Se3 composition. In order to compare the results with those previously obtained on undoped thin films, Cu-doped Sb2Se3 films were deposited both on Mo- and Fluorine-doped Tin Oxide (FTO) substrates, which have different influences on the film crystallization and grain orientation. From the current-voltage analysis it was determined that the introduction of Cu in the Sb2Se3 absorber enhanced the open circuit voltage (VOC) up to remarkable values higher than 500 mV, while the free carrier density became two orders of magnitude higher than in pure Sb2Se3-based solar cells.

Semiconductor Multimaterial Optical Fibers for Biomedical Applications

Integrated sensors and transmitters of a wide variety of human physiological indicators have recently emerged in the form of multimaterial optical fibers. The methods utilized in the manufacture of optical fibers facilitate the use of a wide range of functional elements in microscale optical fibers with an extensive variety of structures. This article presents an overview and review of semiconductor multimaterial optical fibers, their fabrication and postprocessing techniques, different geometries, and integration in devices that can be further utilized in biomedical applications. Semiconductor optical fiber sensors and fiber lasers for body temperature regulation, in vivo detection, volatile organic compound detection, and medical surgery will be discussed.

A Novel Multi-Sulfur Source Collaborative Chemical Bath Deposition Technology Enables 8%-Efficiency Sb2 S3 Planar Solar Cells

Sb₂ S₃ as a light-harvesting material has attracted great attention for applications in both single-junction and tandem solar cells. Such solar cell has been faced with current challenge of low power conversion efficiency (PCE), which has stagnated for 8 years. It has been recognized that the synthesis of high-quality absorber film plays a critical role in efficiency improvement. Here, using fresh precursor materials for antimony (antimony potassium tartrate) and combined sulfur (sodium thiosulfate and thioacetamide), a unique chemical bath deposition procedure is created. Due to the complexation of sodium thiosulfate and the advantageous hydrolysis cooperation between these two sulfur sources, the heterogeneous nucleation and the S^2- releasing processes are boosted. As a result, there are noticeable improvements in the deposition rate, film morphology, crystallinity, and preferred orientations. Additionally, the improved film quality efficiently lowers charge trapping capacity, suppresses carrier recombination, and prolongs carrier lifetimes, leading to significantly improved photoelectric properties. Ultimately, the PCE exceeds 8% for the first time since 2014, representing the highest efficiency in all kinds of Sb₂ S₃ solar cells to date. This study is expected to shed new light on the fabrication of high-quality Sb₂ S₃ film and further efficiency improvement in Sb₂ S₃ solar cells.

Crystal Growth Promotion and Defect Passivation by Hydrothermal and Selenized Deposition for Substrate-Structured Antimony Selenosulfide Solar Cells

Antimony sulfide-selenide (Sb₂(S,Se)₃) is a promising light-harvesting material for stable and high-efficiency thin-film photovoltaics (PV) because of its excellent light-harvesting capability, abundant elemental storage, and excellent stability. This study aimed to expand the application of Sb₂(S,Se)₃ solar cells with a substrate structure as a flexible or tandem device. The use of a hydrothermal method accompanied by a postselenization process for the deposition of Sb₂(S,Se)₃ film based on the solar cell substrate structure was first demonstrated. The mechanism of postselenization treatment on crystal growth promotion of the Sb₂(S,Se)₃ film and the defect passivation of the Sb₂(S,Se)₃ solar cell were revealed through different characterization methods. The crystallinity and the carrier transport property of the Sb₂(S,Se)₃ film improved, and both the interface defect density of the Sb₂(S,Se)₃/CdS interface and the bulk defect density of the Sb₂(S,Se)₃ absorber decreased. Through these above-mentioned processes, the transport and collection of electronics can be improved, and the defect recombination loss can be reduced. By using postselenization treatment to optimize the absorber layer, Sb₂(S,Se)₃ solar cells with the configuration SLG/Mo/Sb₂(S,Se)₃/CdS/ITO/Ag achieved an efficiency of 4.05%. This work can provide valuable information for the further development and improvement of Sb₂(S,Se)₃ solar cells.

Post-Treatment of TiO2 Film Enables High-Quality Sb2Se3 Film Deposition for Solar Cell Applications

The TiO2 thin film is considered as a promising wide band gap electron-transporting material. However, due to the strong Ti-O bond, it displays an inert surface characteristic causing difficulty in the adsorption and deposition of metal chalcogenide films such as Sb2Se3. In this study, a simple CdCl2 post-treatment is conducted to functionalize the TiO2 thin film, enabling the induction of nucleation sites and growth of high-quality Sb2Se3. The interfacial treatment optimizes the conduction band offset of TiO2/Sb2Se3 and leads to an essentially improved TiO2/Sb2Se3 heterojunction. With this convenient interface functionalization, the power conversion efficiency of the Sb2Se3 solar cell is remarkably improved from 2.02 to 6.06%. This study opens up a new avenue for the application of TiO2 as a wide band gap electron-transporting material in antimony chalcogenide solar cells.

Sb2 Se3 Thin-Film Solar Cells Exceeding 10% Power Conversion Efficiency Enabled by Injection Vapor Deposition Technology

Binary Sb₂ Se₃ semiconductors are promising as the absorber materials in inorganic chalcogenide compound photovoltaics due to their attractive anisotropic optoelectronic properties. However, Sb₂ Se₃ solar cells suffer from complex and unconventional intrinsic defects due to the low symmetry of the quasi-1D crystal structure resulting in a considerable voltage deficit, which limits the ultimate power conversion efficiency (PCE). In this work, the creation of compact Sb₂ Se₃ films with strong [00l] orientation, high crystallinity, minimal deep level defect density, fewer trap states, and low non-radiative recombination loss by injection vapor deposition is reported. This deposition technique enables superior films compared with close-spaced sublimation and coevaporation technologies. The resulting Sb₂ Se₃ thin-film solar cells yield a PCE of 10.12%, owing to the suppressed carrier recombination and excellent carrier transport and extraction. This method thus opens a new and effective avenue for the fabrication of high-quality Sb₂ Se₃ and other high-quality chalcogenide semiconductors.

Rapid thermal annealing process for Se thin-film solar cells

Recently, selenium (Se) has regained interest as possible wide-bandgap photovoltaic material for silicon-based tandem applications. However, the easy sublimation of Se below the melting point (220 °C) brings challenges for...