Sb2Se3 Solar Cells Research Articles

Reflection and lattice mismatch loss analysis in Sb2Se3 solar cells

Antimony chalcogenide thin film solar cells have been considered promising candidates in the field of photovoltaics, because of their suitable physical and chemical properties. However, the reported experimental record efficiency is far from the corresponding theoretical value. Multiple works have been directed to increase the efficiency of these devices; however, to the best of our knowledge, studies related to losses due to the reflection of the incident radiation in conjunction with the effects of the lattice mismatch of the constituent layers of the solar cells in the formation of interfacial states have not been addressed. Considering these aspects, this work presents a study of reflection losses caused by the layers of materials typically used for processing of solar cells based on Sb2Se3 and a description of the influence of lattice mismatch in the formation of interfacial states, evaluating the impact of both aspects on the efficiency.

Classification of lattice defects and the microscopic origin of p-type conductivity of Sb2Se3 solar cell absorber with varying Al2O3-layer thicknesses

Based on first-principles calculations, herein, we reveal the origin of p-type conductivity and the roles of Al and O in the enhancement of hole concentration in Sb2Se3 thin films. A new class of low-energy defects with shallow acceptor levels is presented by substituting Se with O and inducing Sb vacancy [OSe–VSb] complex. Moreover, the concentration of holes induced by the intrinsic and extrinsic defects is calculated and discussed. Our results can explain the intriguing experimental observation where the hole concentration is enhanced after Al2O3 capping and provide a new insight to the defect chemistry and physics of Sb2Se3 thin films. In addition, Al2O3 layers with varying thicknesses have been deposited on the surface of Sb2Se3 films. The crystallinity, orientation and electrical properties of Sb2Se3 films have been investigated in detail. Lastly, 6.87% efficiency of Sb2Se3 solar cells without other optimization has been obtained based on the structure of FTO/CdS (CBD)/Sb2Se3/Al2O3/Au.

Post‐deposition annealing and interfacial atomic layer deposition buffer layers of Sb2Se3/CdS stacks for reduced interface recombination and increased open‐circuit voltages

AbstractCurrently, Sb2Se3 thin films receive considerable research interest as a solar cell absorber material. When completed into a device stack, the major bottleneck for further device improvement is the open‐circuit voltage, which is the focus of the work presented here. Polycrystalline thin‐film Sb2Se3 absorbers and solar cells are prepared in substrate configuration and the dominant recombination path is studied using photoluminescence spectroscopy and temperature‐dependent current–voltage characteristics. It is found that a post‐deposition annealing after the CdS buffer layer deposition can effectively remove interface recombination since the activation energy of the dominant recombination path becomes equal to the bandgap of the Sb2Se3 absorber. The increased activation energy is accompanied by an increased photoluminescence yield, that is, reduced non‐radiative recombination. Finished Sb2Se3 solar cell devices reach open‐circuit voltages as high as 485 mV. Contrarily, the short‐circuit current density of these devices is limiting the efficiency after the post‐deposition annealing. It is shown that atomic layer‐deposited intermediate buffer layers such as TiO2 or Sb2S3 can pave the way for overcoming this limitation.

Routes to increase performance for antimony selenide solar cells using inorganic hole transport layers

Simple compound antimony selenide (Sb2Se3) is a promising emergent light absorber for photovoltaic applications benefiting from its outstanding photoelectric properties. Antimony selenide thin film solar cells however, are limited by low open circuit voltage due to carrier recombination at the metallic back contact interface. In this work, solar cell capacitance simulator (SCAPS) is used to interpret the effect of hole transport layers (HTL), i.e., transition metal oxides NiO and MoO x thin films on Sb2Se3 device characteristics. This reveals the critical role of NiO and MoO x in altering the energy band alignment and increasing device performance by the introduction of a high energy barrier to electrons at the rear absorber/metal interface. Close-space sublimation (CSS) and thermal evaporation (TE) techniques are applied to deposit Sb2Se3 layers in both substrate and superstrate thin film solar cells with NiO and MoO x HTLs incorporated into the device structure. The effect of the HTLs on Sb2Se3 crystallinity and solar cell performance is comprehensively studied. In superstrate device configuration, CSS-based Sb2Se3 solar cells with NiO HTL showed average improvements in open circuit voltage, short circuit current density and power conversion efficiency of 12%, 41%, and 42%, respectively, over the standard devices. Similarly, using a NiO HTL in TE-based Sb2Se3 devices improved open circuit voltage, short circuit current density and power conversion efficiency by 39%, 68%, and 92%, respectively.

Reactively sputtered CdS:O buffer layers for substrate Sb2Se3 solar cells

Antimony selenide (Sb2Se3) is an emerging and promising photovoltaic material. High controllability for the energy level of buffer layers is greatly desirable for achieving higher performance Sb2Se3 solar cells due to the formation of heterojunction at the buffer/Sb2Se3 absorber interface. In this work, the CdS:O buffers were prepared by using a reactive sputtering technique including an Ar/O2 mixture gas and a CdS ceramic target, and a composite buffer were fabricated with a structure of CBD-CdS (∼10 nm)/CdS:O. The interface damage induced by sputtering is investigated, and untra-thin CBD-CdS is performed to recover the plasma induced damage at the CdS:O/Sb2Se3 heterojunction interface. By optimizing the S/(S+O) composition ratio and the phase component of the composite buffer, wide band-gap buffer layers were achieved, and the device spectra response and device parameters JSC and VOC were improved. It was found that the composite CdS:O buffer optimizes the heterojunction interface band alignment and further efficiently reduce the interface recombination, enhanced the transfer and collection of photogenerated carriers.

Numerical Simulation of the Performance of Sb2Se3 Solar Cell via Optimizing the Optoelectronic Properties Based SCAPS-1D.

Antimony trisulfide (Sb2Se3), a non-toxic and accessible substance, has possibilities as a material for use in solar cells. The current study numerically analyses Sb2Se3 solar cells through the program Solar Cell Capacitance Simulator (SCAPS). A detailed simulation and analysis of the influence of the Sb2Se3 layer’s thickness, defect density, band gap, energy level, and carrier concentration on the devices’ performance are carried out. The results indicate that a good device performance is guaranteed with the following values in the Sb2Se3 layer: an 800 optimal thickness for the Sb2Se3 absorber; less than 1015 cm−3 for the absorber defect density; a 1.2 eV optimum band gap; a 0.1 eV energy level (above the valence band); and a 1014 cm−3 carrier concentration. The highest efficiency of 30% can be attained following optimization of diverse parameters. The simulation outcomes offer beneficial insights and directions for designing and engineering Sb2Se3 solar cells.

Interfacial Engineering towards Enhanced Photovoltaic Performance of Sb2Se3 Solar Cell

AbstractAntimony selenide (Sb2Se3) is a kind of emerging candidate for the application in low‐cost and high‐efficiency thin film solar cells owing to its non‐toxicity, earth‐abundance, and unique quasi‐1D crystal structure. In this photovoltaic material, quasi‐vertically oriented Sb2Se3 thin films can transfer photocarriers efficiently along the [hk1]‐orientation. However, the crystal orientation control in thin films is still the main obstacle to improve the efficiency of Sb2Se3 solar cells. Herein, an interfacial engineering method is developed by antimony chloride (SbCl3) on CdS films with post‐annealing treatment to improve the quality of both interface and absorber thin film. It is found that the SbCl3 treatment resulted in 1) transformation of the CdS/Sb2Se3 interface from “cliff” to “spike” like energy band alignments; 2) improved surface morphology of CdS surface, and 3) suppressed cubic structure of CdS structure and thus generating improved [hk1]‐oriented Sb2Se3 film on the high‐purity hexagonal CdS. As a result, the Sb2Se3 solar cell treated with SbCl3 achieves a top efficiency of 6.89% in superstrate planar heterojunction Sb2Se3 solar cell. This study provides a new interfacial post‐treatment method for the preparation of high‐performance Sb2Se3 planar heterojunction solar cells.

Interface engineering of antimony selenide solar cells: a review on the optimization of energy band alignments

Earth-abundant and environmentally benign antimony selenide (Sb2Se3) has emerged as a promising light-harvesting absorber for thin-film photovoltaic (PV) devices due to its high absorption coefficient, nearly ideal bandgap for PV applications, excellent long-term stability, and intrinsically benign boundaries if properly aligned on the substrate. The record power conversion efficiency of Sb2Se3 solar cells has currently reached 9.2%, however, it is far lower than the champion efficiencies of other chalcogenide thin-film solar cells such as CdTe (22.1%) and Cu(In,Ga)Se2 (23.35%). The inferior device performance of Sb2Se3 thin-film solar cells mainly results from a large open-circuit voltage deficit, which is strongly related to the interface recombination loss. Accordingly, constructing proper band alignments between Sb2Se3 and neighboring charge extraction layers through interface engineering to reduce carrier recombination losses is one of the key strategies to achieving high-efficiency Sb2Se3 solar cells. In this review, the fundamental properties of Sb2Se3 thin films, and the recent progress made in Sb2Se3 solar cells are outlined, with a special emphasis on the optimization of energy band alignments through the applications of electron-transporting layers and hole-transporting layers. Furthermore, the potential research directions to overcome the bottlenecks of Sb2Se3 thin-film solar cell performance are also presented.

Analysis and design of p-n homojunction Sb2Se3 solar cells by numerical simulation

Antimony selenide (Sb2Se3) is considered a promising candidate utilized as an absorber in thin film solar cell (TFSC) technology thanks to its non-toxic and earth-abundant nature besides its reported high absorption coefficient. To enhance the power conversion efficiency (PCE) of Sb2Se3 solar cells, we report some design suggestions by applying device simulation. The numerical model is firstly validated by calibration of simulation results vs those from an experimental Sb2Se3 solar cell structure composed of FTO/CdS/Sb2Se3/Au where CdS serves as an electron transport layer (ETL). Then, the cell is modified to include an embedded p-n homojunction. In contrast to the conventional heterostructure design, a homojunction structure has crucial benefits in terms of both electronic and optoelectronic characteristics such as the extra produced built-in electric field which can increase the transport of photogenerated carriers. Three device configurations are presented and compared. The first and the second cases are when using CdS and ZnOS as ETLs. Utilizing ZnOS ternary compound is found to be more beneficial as its conduction band offset with the absorber layer could be tuned to attain a proper cliff-like band alignment. The third case is when considering homojunction design free from all carrier transport layers. Possible paths for device optimization are investigated to boost the efficiency in a try to overcome the efficiency bottleneck encountered in the Sb2Se3-based quasi homojunction solar cells. All simulations, performed in this study, are done by SCAPS device simulation software under standard AM1.5G one Sun illumination.

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.

Energy band alignment for Cd-free antimony triselenide substrate structured solar cells by Co-sputtering ZnSnO buffer layer

Antimony selenide (Sb2Se3) have developed as an environmental-friendly photoactive materials for low-cost photovoltaics due to its non-toxic elements and excellent optoelectronic properties. However, chemical bath deposited (CBD) CdS thin film was generally employed as electron transport layer (ETL) in substrate or superstrate structured Sb2Se3 solar cells, which was still a huge concern restraining its long-term advancement. In this work, we have replaced the toxic CdS film by employing ZnSnO films fabricated through magnetron co-sputtering technique to develop Cd-free ZnSnO/Sb2Se3 solar cells. It was observed that Sn/(Zn + Sn) in ZnSnO film affecting the energy band alignment with Sb2Se3 take part in improving the device efficiency. Substrate structured Cd-free Sb2Se3 based devices with a champion device performance of 3.44%, were firstly made with the optimized Zn0.57Sn0.43O buffer layer closely related to the rational band alignment, the reduced recombination losses at interface (ZnSnO/Sb2Se3), and efficient charge transfer. This substituted sputtering ZnSnO for CBD-CdS film demonstrated remarkable potential to efficient and Cd-free Sb2Se3 solar cell with full-vacuum process.

Numerical analysis of hole transport layer-free antimony selenide solar cells: Possible routes for efficiency promotion

Amongst the numerous absorbers confronted in thin-film solar cell technology, antimony selenide (Sb2Se3) is regarded as an extremely promising contender as it is a non-toxic and earth-abundant besides its high-level absorption coefficient. To boost the power conversion efficiency (PCE) of Sb2Se3 solar cells, we report some design recommendations by utilizing device simulation. The device model is firstly validated by calibration of an experimental cell having a configuration of FTO/CdS/Sb2Se3/Spiro-OMeTAD/Au. Then, the optimization of a hole transport layer (HTL) free structure is carried out by tuning the conduction band offset between the electron transport layer (ETL) and the Sb2Se3 absorber and by inspecting the key absorber parameters to get the maximum available power conversion efficiency. In this context, the ternary compound material ZnMgO is found to match the optimum band alignment. Moreover, the impact of ETL parameters, like thickness, doping, and surface treatment by ammonia etching, has been analyzed to understand its underlying physics and to provide possible ways for device efficiency promotion. All simulations, conducted in this paper, are accomplished by SCAPS device simulation software under standard one Sun (AM1.5G, 100 mW/cm2) illumination at 300 K.

Enhanced Efficiency and Stability in Sb2S3 Seed Layer Buffered Sb2Se3 Solar Cells

AbstractAntimony selenide (Sb2Se3) has excellent directional optical and electronic behaviors due to its quasi‐1D nanoribbons structure. The photovoltaic performance of Sb2Se3 solar cells largely depends on the orientation of the nanoribbons. It is desired to grow these Sb2Se3 ribbons normal to the substrate to enhance photoexcited carrier transport. Therefore, it is necessary to develop a strategy for the vertical growth of Sb2Se3 nanoribbons to achieve high‐efficiency solar cells. Since antimony sulfide (Sb2S3) and Sb2Se3 are from the same space group (Pbnm) and have the same crystal structure, herein an ultrathin layer (≈20 nm) of Sb2S3 has been used to assist the vertical growth of Sb2Se3 nanoribbons to improve the overall efficiency of Sb2Se3 solar cell. The Sb2S3 thin layer deposited by the hydrothermal process helps the Sb2Se3 ribbons grow normal to the substrate and increases the efficiency from 5.65% to 7.44% through the improvement of all solar cell parameters. This work is expected to open a new direction to tailor the Sb2Se3 grain growth and further develop the Sb2Se3 solar cell in the future.

Ten Years of Sb2Se3 Thin Film Solar Cells

Antimony selenide (Sb2Se3) has emerged as a promising absorber material for photovoltaic application. Since the first pure‐phase Sb2Se3 solar cell reported ten years ago, increasing research has been carried out on this system with the device efficiency now reaching 9.2%. This work aims to present the major milestones of Sb2Se3 thin film solar cells from its birth to the present, including the selection of Sb2Se3 for thin film photovoltaics, the choice of planar device configuration instead of sensitized device, switching from solution processing to vacuum processing, new concept of orientation control and benign grain boundaries, discovery of unusual and complex defects, and post selenization for defect passivation. In the end, the authors discuss the competitive applications of Sb2Se3 solar cells in flexible devices and outlook their future development.

N-Si/p-Sb2Se3 structure based simple solar cell device

Sb2Se3 is a p-type semiconductor that has been widely used as an absorber layer in thin film solar cells. For this study, Sb2Se3 was made using the solid-state reaction route, and thin films were deposited by the thermal evaporation method at room temperature and annealed at various temperatures. The crystallinity of Sb2Se3 thin films improved after annealing. The material and thin films were characterized by XRD, Raman, SEM, and UV–Vis spectroscopy to study their structural and optical properties. A simple device structure that can be made using a thermal evaporation system is proposed. We have accomplished simulation work based on Sb2Se3/c-Si hetero-junction photovoltaic cells using SCAPS-1D. In the simulation, experimental data of Sb2Se3, including its band gap, thickness, and absorption coefficient, have been introduced. The simulation is used to extract the parameters, such as back contact work function, electron affinity, and the thickness of the p-Sb2Se3 layer and n-Si layer, which is also varied and optimized to improve the device's performance. p-Sb2Se3 with a band gap of 1.64 eV showed a maximum efficiency of 12.75% at the optimized conditions. As n-Si is commercially available, this simple device structure can have multiple local applications. It can be considered a reliable method for predicting photovoltaic performance for future studies, such as improving the efficiency of Sb2Se3 solar cells or trying out a new tandem solar cell structure using Sb2Se3.

Back contact modification in Sb2Se3 solar cells: The effect of a thin layer of MoSe2

The record efficiency reported for Sb2Se3 solar cells is 9.2% and different lines of work have been opened with the aim of overcoming the factors that limit this value. Between them, the back contact is one of the aspects that must be considered to improve the efficiency of solar cells. In this work, the effect of forming an intermediate layer between the back contact of Mo and the Sb2Se3 absorber is studied and its impact on the properties of solar cells processed in substrate configuration: glass/Mo/Sb2Se3/CdS/i-ZnO/ITO, is evaluated. For the study, a series of photovoltaic devices were processed in which selenization processes were carried out in the molybdenum contact under different thermal annealing temperatures in the range of 320 to 400°C to produce the MoSe2 compound. The influence of these thermal processes based on Sb2Se3 structural properties and the electro-optical properties of solar cells was evaluated. The results revealed that by the introduction of MoSe2, through the selenization of the Mo, the electrical properties of the solar cells are improved, with the best efficiency solar cell of 5.0%. According to our analysis, it is considered that the optimization of the electrical parameters is a consequence of the behavior of MoSe2 as a hole transport layer, giving rise to a n-i-p structure whose internal electrical field is found further within the absorber, which makes the carrier separation process more efficient and prevents recombination. On the other hand, to evaluate the thickness of the MoSe2 layer and determine the physical processes that limit the efficiency of the devices, a simulation process was carried out based on the experimental results.

Enhanced charge carrier transport via efficient grain conduction mode for Sb2Se3 solar cell applications

The combination of the SnO2 and Sb2Se3 offers an alternative strategy for realizing the n-p heterojunction in Sb2Se3 thin-film solar cells. However, the low conductivity of the SnO2 and the lateral growth of Sb2Se3 grains make carrier extraction more challenging, thereby resulting in unsatisfactory device performance. In this study, the improvement of the Sb2Se3 solar cell performance is achieved by enhancing the conductivity of the SnO2 and rearranging the Sb2Se3 elongated grains simultaneously so that the carriers can be efficiently transmitted through the grain conduction mode instead of the grain boundary conduction mode. Furthermore, the evolution of (Sb4Se6)n ribbons from pure lateral growth to longitudinal growth is observed by adjusting the distribution of doping elements on the SnO2 surface. Finally, under optimal treatment times, the carrier recombination in the heterojunction is effectively inhibited by building an efficient electron-transport channel, and the Sb2Se3 solar cell achieved the highest power conversion efficiency of 5.41%. Our study clarifies the relationship between carrier transport and grain orientation in one-dimensional Sb2Se3 materials and realized the effective adjustment of the (Sb4Se6)n ribbon growth direction. The outcomes of this study provide guidance for the control of carrier behavior in optoelectronic devices with similar one-dimensional absorber materials.

Interface Modification Uncovers the Potential Application of SnO2/TiO2 Double Electron Transport Layer in Efficient Cadmium‐Free Sb2Se3 Devices

AbstractAn undesirable p–n heterojunction interface of Sb2Se3 absorber with Cd‐free electron transport layer (ETL) is one of the key problems hindering the efficiency improvement of Sb2Se3 solar cell. Herein, a promising SnO2/TiO2 ETL coupled with SbCl3 treatment is introduced to improve the performance of Sb2Se3 solar cell. The mechanism of SbCl3 treatment on the crystal orientation of Sb2Se3 thin film and the p–n heterojunction interface of Sb2Se3 solar cell is disclosed combined with different characterization methods. The carrier transport property for Sb2Se3 thin film is enhanced, and the conduction band offset (CBO) of TiO2/Sb2Se3 interface is reduced from 0.57 to 0.20 eV by forming Sb2O3 interlayer at TiO2/Sb2Se3 interface after SbCl3 treatment, by which the interface recombination and the open circuit voltage deficit of the device can be effectively decreased, and the interface bonding at TiO2/Sb2Se3 interface can be effectively improved. Ultimately, the Cd‐free Sb2Se3 solar cell with configuration of ITO/SnO2/TiO2/Sb2Se3/Au achieves an efficiency of 5.82%, which is the highest efficiency in vapor transport deposition (VTD)‐processed Cd‐free Sb2Se3 solar cell at present. This work is expected to fill in the blank of VTD‐processed Cd‐free Sb2Se3 solar cell and offers a valuable reference for future band alignment of Sb2Se3 solar cell.

Vanadium-doped indium tin oxide window layer in Sb2Se3 solar cell

Antimony selenide (Sb2Se3) is an emerging photovoltaic material. Indium tin oxide (ITO) is commonly used as the window layer material in Sb2Se3 solar cells; however, ITO films have poor absorption in the near-infrared spectrum. Our objective in this research was to replace conventional ITO with vanadium-doped indium tin oxide (ITO:V) to improve the near-infrared light transmittance of Sb2Se3 thin film solar cells and thereby enhance the efficiency of solar cells. The experiment parameters included vanadium doping concentration and annealing temperature. ITO films doped with 0.35 at.% V and annealed at 100 °C for 30 min outperformed conventional ITO films in terms of photovoltaic performance. The proposed scheme improved light transmittance from 80.03% to 83.02% over a wavelength range of 400–1100 nm, which led to a significant improvement in Jsc and device efficiency (from 4.5% to 5.6%). It appears that ITO films can be doped with vanadium to improve transmittance by reducing refractive index degradation in the near-infrared region.