High-efficiency Thin-film Solar Cells Research Articles

Bandgap-graded Cu2Sn1-xGexS3 thin film solar cells prepared by sputtering SnGe/Cu targets

Cu2Sn1-xGexS3 (CTGS) thin films were created through sulfurizing SnGe/Cu precursors deposited by the sputtering method. The effects of different sulfurization conditions on the crystallinity, morphology, composition, optical-electrical properties and chemical information of the CTGS thin films have been investigated in detail. The results demonstrate that the CTGS thin films obtained by using sulfurization temperature at 550 °C for 20min have the best crystal quality and smooth surface morphology with largest grains and the best optical-electrical properties. Meanwhile, CTGS thin films solar cell with the best performance is found that the CTGS film possesses a graded band gap structure, in which the band gap gradually become larger towards the Mo electrode, and the CdS/CTGS hetero-junction interface shows the “type I″ energy band alignment with a “spike-like” structure. As a result, the obtained bandgap-graded CTGS thin film solar cells with the best power conversion efficiency (PCE) of 3.35 (±0.04) % manifest an open-circuit voltage of 389 (±7.78) mV and a short-circuit current density of 26.98 (±0.54) mA cm−2. This work demonstrates a promising route to develop high-efficiency Cu(In,Ga)Se2 or Cu2SnS3-based thin film solar cells.

Influence of Stacking Order on the Structural and Optical Properties of Cu2ZnSnS4 Absorber Layer Prepared from DC-Sputtered Oxygenated Precursors

Several studies have attempted to overcome the sudden volume expansion of the precursor during sulfurization by the use of oxygen-containing precursors when growing the CZTS absorber. This work demonstrates the influence of precursor stacking orders on the properties of the CZTS thin film absorber layer from DC-sputtered oxygenated precursors for solar cell applications. CZTS absorber layers were prepared from three types of DC-sputtered stacks, namely, Zn-O/Sn/Cu, Sn/Zn-O/Cu, and Sn/Cu/Zn-O. The precursors were sequentially deposited on a soda lime glass (SLG) using DC-magnetron sputtering and annealed in a sulfur and nitrogen ambient. X-ray diffractometry (XRD) and Raman spectroscopy analyses reveal the formation of crystalline kesterite CZTS structure regardless of the precursor stacking order. Atomic force microscope (AFM) analysis showed that CZTS thin films grown from precursor stacks SLG/Zn-O/Sn/Cu and SLG/Sn/Zn-O/Cu had improved morphological properties with densely packed large grains compared to that with stack SLG/Sn/Cu/Zn-O. SLG/Zn-O/Sn/Cu is the best stack among the studied stacking orders since it exhibits large grains in the absorber layer, which is preferential for high-efficiency thin film solar cells. The use of oxygenated precursor with order Sn/Zn-O/Cu promises improved CZTS absorber properties as it exhibits better morphological properties.

SCAPS numerical design of MoSe2 solar cell for different buffer layers

The solar cell capacitance simulator (SCAPS-1D) has been used to simulate, design and analyze of MoSe2, an attractive transition metal dichalcogenide (TMDC) material, based heterojunction solar cells to use it as a potential alternative to conventional absorber layers used in solar cells. The work also focuses on finding optimal absorber, buffer layer thickness and impact of operating temperature on solar cell performance with a possible replacement to toxic CdS buffer layer. It has been obtained that the optimum thickness of MoSe2 absorber layer is 1 µm and buffer layer is about 0.04 µm. The efficiency obtained with CdS based buffer layer solar cell is 20.21%. Among different buffer layers such as In2S3, ZnO, ZnOS and ZnSe, the highest efficiency obtained of MoSe2 based solar cell is 20.58% with ZnO buffer layer. ZnO buffer based solar cell shows a temperature gradient of -0.355%/K compared to -0.347%/K for CdS buffer based solar cell. The findings of this work provide important guidance to fabricate high-efficiency MoSe2 thin film solar cell with non-toxic ZnO as a potential buffer layer.

InGaN based Schottky barrier solar cell: Study of the temperature dependence of electrical characteristics

The indium gallium nitride (InGaN) semiconductor alloy shows great promise for high-efficiency thin-film solar cells due to its intrinsic characteristics. However, there are major challenges in the development of high-quality p-doped and indium-rich InGaN layers to fabricate a pn or pin solar cell. This study focuses on the development of an alternative structure, not requiring p-doping, with a Schottky contact on n-type InGaN. The InGaN absorber was grown by metalorganic chemical vapor deposition and its structural, morphological and optical properties studied. Structural analysis by X-ray diffraction showed the growth of single crystal layers without phase separation. Indium compositions which vary up to around 8.3 % were confirmed by transmission measurements. The formation of V-shaped pits was observed with increased indium composition at lower growth temperatures. Schottky diodes based on InGaN with platinum metallic contacts were fabricated and their current–voltage characteristics studied in detail as a function of temperature. This analysis of the conduction mechanisms in Schottky/InGaN devices permitted in particular the extraction of the diode parameters as a function of the temperature showing a high rectification with an ideality factor of 1.15 with reverse saturation current of 6.7×10−9A at room temperature for an indium composition of 5.52 %. In addition, the analysis revealed the presence of a dual Gaussian distribution of barrier heights in a specific temperature range. Finally, the incident photon-to-electron conversion efficiency (IPCE) of the fabricated InGaN Schottky solar cells, measured using intensity-modulated photocurrent spectroscopy, reached a peak value of 51 %, which is among the highest published values for InGaN based solar cells.

Self-assembled growth of quasi-vertically oriented Sb2S3 thin films for substrate structured solar cells

Antimony sulfide (Sb2S3) is an appealing one-dimensional light-harvesting material for thin-film solar cells due to the high absorption coefficient, suitable bandgap and abundance of constituent elements. The orientation of the Sb2S3 thin film is considered as one of the most important factors affecting the performance of the device. According to the minimum energy principle, Sb2S3 is prone to grow parallel to the substrate along the [hk0] orientation which is harmful to the device performance. On the other hand, [hk1]-oriented films are much more beneficial but additional processes such as annealing are often required. In this work, stoichiometric Sb2S3 thin films consist of compact, highly [hk1]-oriented grains have been prepared via a self-assembled growth by magnetron sputtering and post-sulfurization. After carefully optimized the preparation process, a champion device (2.89% power conversion efficiency) was obtained with an open-circuit voltage of 696 mV and a short-circuit current density of 12.48 mA/cm2 under AM 1.5G solar radiation. Interestingly, the high open-circuit voltage of our device is already comparable to the state-of-the-art Sb2S3 solar cells. This work demonstrates a great potential of the sputtering and post-sulfurization method in fabrication of high-efficiency substrate Sb2S3 thin-film solar cells.

GaAs thin-film solar cells for perfect absorption in the visible and near-infrared bands

Improving the solar cell's ability to capture solar photons and enhancing its absorption of light have a significant impact on increasing the photoelectric conversion efficiency (PCE) of solar cells. In this study, we propose to embed a layer of light-trapping structure (LTS) utilizing Ti nanoparticles and their oxide TiO2 periodically arranged in the window layer of GaAs thin-film solar cells. This structure improves the light absorption efficiency by increasing the optical range and surface plasmon resonance of light inside the cell, which in turn improves the PCE of the solar cell. Simulation results show that the GaAs solar cell proposed in this paper achieves an average absorptivity of 94.99% in the visible and near-infrared wavelength bands, and the PCE reaches 31.77%, which is close to the Shockley-Queisser limit level of the single-junction solar cell. And it realizes the characteristic of perfect absorption in the wavelength range of 555–800 nm. The cell structure proposed in this study is characterized by high bandwidth perfect absorption and high PCE, which is insensitive to the angle of incidence, and provides a new idea for the design of new high-efficiency thin-film solar cells.

Mechanosynthesis of semiconductor nanocrystalline Cu2ZnSnSe4 for solar cells

Cu2ZnSnSe4 is a promising material that can be used to make low-cost, high-efficiency thin-film solar cells. The present study, we established a simple and efficient approach for producing a single-phase Cu2ZnSnSe4 bulk material from fundamental precursors (Cu, Zn, Sn and Se) using dry ball milling. After every two hours of the dry milling process, X-Ray Diffraction (XRD) and Raman Spectroscopy investigations were carried out to investigate the movement towards single phase Cu2ZnSnSe4 and the concurrent secondary phase depletion. The development of Cu2ZnSnSe4 materials that crystallize in a Kesterite system is shown by the prominent diffraction peaks. The crystalline size of the materials is 10–20 nm and dislocation density is 3.02–3.22 ×1015 lines/m2. UV–Vis spectroscopy was used to investigate the optical properties of the materials. Using transmittance and reflectance data, the linear and nonlinear optical constants of Cu2ZnSnSe4 films were calculated and the bandgap value is 1.6 eV. Hence from these results we can conclude that the above synthesized powder can be used for the development of thin films via thermal or electron beam evaporations on desired substrate and also we can use for various energy harvesting applications as a photoabsorber.

High-efficiency Sb2Se3 thin-film solar cells based on Cd(S,O) buffer layers prepared via spin-coating

CdS films prepared via chemical bath deposition exhibit extremely good performance as a buffer layer of chalcogenide solar cells. However, their commercial application is very limited because of the production of a large amount of wastewater containing cadmium. In this study, we develop an efficient way to prepare CdS films using the spin-coating technique. The spin solution is anhydrous, and the oxygen content can be well controlled by changing the Cd/S content ratio in the solution. The crystal structure, morphology, and optical and electrical properties of CdS films with different Cd/S content ratios are characterized. The effect of the oxygen content on the device performance is investigated. We find that the introduction of an appropriate amount of oxygen can improve the carrier transport efficiency by decreasing the interface recombination. The spin-coated CdS films have good coverage of the substrate for film thicknesses below 50 nm. By the optimizing of Cd/S content ratio, we achieve an improved efficiency of 5.76% for the Sb2Se3 solar cells. This preparation technique is sufficiently simple for large-scale processing and produces much less wastewater containing cadmium; thus, it is promising for application to future large-scale solar cell production.

Design of n-CdS/p-CuInTe2/p + -MoS2 thin film solar cell with a power conversion efficiency of 34.32%

Copper indium telluride (CuInTe2)-based n-CdS/p-CuInTe2/p + -MoS2 double-heterostructure solar cell has been investigated numerically by solar cell capacitance simulator (SCAPS-1D). Initially, an adjusted condition among the most influencing parameters e.g. thickness, carrier doping level, and bulk defects of active materials such as CdS window, CuInTe2 absorber, and p + -MoS2 back surface field (BSF) layers has been obtained by a systematic computation. The proposed solar cell exhibits an improved power conversion efficiency (PCE) of 34.32% with VOC =0.927 V, JSC = 42.50 mA/cm2, and FF = 87.14% under the optimized condition. The PCE can be further enhanced to 38.87% introducing sub-bandgap absorption in the MoS2 (300 nm) BSF with Urbach energy, E0 of 0.4 eV. These detailed simulation results reveal a huge potential of CuInTe2 absorber with MoS2 BSF layer for the manufacture of a cost-effective, high-efficiency double-heterojunction thin film solar cell.

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.

An innovative design of arrays-interpenetrated CZTSSe/MoO3 back interfacial contacts for improving the solar cell performance

It is widely known that the challenge of making good electrical contact at the back electrode interface will always follow us for high-efficient kesterite-type CZTSSe thin-film solar cells. Aiming at clarifying the correlation of device performance on the micro-structure of back interface, we come up with a new fresh design that introducing in-situ anodized MoO 3 porous arrays with regulated structural parameters acts as the back interfacial contact. Regards the such array-structures of interpenetrated CZTSSe and MoO 3 , the study reveals that the overall device performance is closely related to the micro-structure of the MoO 3 interface layer, and the optimized device efficiency can be improved to 9.00% from 6.31% (Ref. Mo-based cells), having a 32% increased J SC together with a 64% increase in FF. The performance improvement mechanism is analyzed in details. The interesting preliminary finding would indicate that the new strategy is very effective to form reliable electrical contact at the back interface for high-efficient CZTSSe solar cells. • New design of interpenetrated CZTSSe/MoO 3 arrays for innovative interfacial contact of CZTSSe solar cells. • Nearly 43% increase of efficiency from 6.31% to 9.00% is achieved. • Increase of J SC from 25.49 to 33.63 mA/cm 2 and FF from 60.4% to 63.65%. • Potential for revealing the effect of back contact structure on device performance.

(Digital Presentation) Preparation of Metal Halide Perovskite Thin Films Via Laser Deposition

We have been preparing metal halide perovskite (hereinafter referred to as perovskite) thin films by laser deposition. In this study, we report the results of our investigation of the effects of laser wavelength and fluence on the deposition process. One of the most important features of perovskites, which have been rapidly developed in recent years as materials for high-efficiency and low-cost thin-film solar cells, is the applicability of a simple process using solution coating under atmospheric pressure [1]. Crystal growth of perovskite by the solution method occurs through equilibrium chemical reactions, enabling the formation of thin films on the order of μm thickness in less than a few seconds; however, it is difficult to systematically control the crystal growth process at the molecular layer level by the solution method. On the other hand, in the physical vapor deposition (PVD) method, although the deposition rate is relatively low, ranging from sub-nanometer to several nm/s, the deposition can be controlled at the molecular layer level, as well as allowing different atoms to be readily introduced into the film. Therefore, the PVD method allows the addition of elements that are difficult to achieve with solution reactions and is suitable for studies that investigate the effects of such elements on physical properties.In laser deposition (LD), one of the PVD methods, materials are irradiated with an infrared (IR) or an ultraviolet (UV) laser beam, and thin films are formed by evaporation through IR heating or ablation with plasma formation through UV electron excitation. The advantage of LD is that it can cause instantaneous heating or ablation by switching on and off laser irradiation only on the material surface, thus enabling the deposition of molecular layers of organic materials with high vapor pressure or high melting point materials such as inorganic oxides with minimal cross-contamination caused by evaporation. We have prepared perovskite thin films by alternate deposition of PbI2 and CH3NH3I (MAI) using an IR laser and solid-phase reaction at room temperature aiming at the detailed investigation of the crystal growth process and introduction of various dopants in perovskite materials. [2, 3]. In this study, we have also performed perovskite film deposition by UV pulsed laser and investigated the difference in the physical properties of the perovskite films compared to those deposited by IR laser.Fig. 1 shows a schematic structure and appearance of the laser deposition system used in this experiment. The experimental method is described below. A synthetic quartz substrate was introduced into an ultra-high vacuum chamber with a base vacuum of 2×10-5 Pa., Then a semiconductor continuous IR laser (wavelength: 808 nm) or a UV pulse laser beam generated by the fourth harmonic of an Nd:YAG Q-Switch laser (wavelength: 266 nm, 10 Hz) was irradiated alternately onto PbI2 and MAI targets to form CH3NH3PbI3.The optical band gap of the thin films deposited by continuous infrared laser deposition shows a change in optical band gap depending on the thickness of the alternately deposited PbI2 and MAI, which can be attributed to the different content ratios of the tetragonal and orthorhombic phases. Interestingly, in UV pulsed laser deposition, the deposition rate was about 0.35 nm/s under the high laser fluence condition with lens focusing, while a high deposition rate of 20 nm/s was obtained under the low laser fluence condition without lens focusing. This result suggests that the excess kinetic energy of the deposition precursor in the case of lens-focused deposition causes re-sputtering on the surface of the already deposited film, resulting in a reduction of the effective deposition rate.In the presentation, we will demonstrate and discuss the results of crystallinity and optical absorption properties.[1] T. Miyasaka, A. Kulkarni, G. M. Kim, S. Öz and A. K. Jena, Adv. Energy Mater. 2020, 11902500 (2020).[2] K. Kawashima, Y. Okamoto, O. Annayev, N. Toyokura, R. Takahashi, M. Lippmaa, K. Itaka, Y. Suzuki, N. Matsuki and H. Koinuma, Science and Technology of Advanced Materials 18, 307 (2017).[3] N. Matsuki, Y. Iida, T. Shimada, Yuta Abeand T. Sato, ECS Meeting abst. MA2020-02, 1860 (2020). Figure 1

Microenvironment Created by SnSe2 Vapor and Pre-Selenization to Stabilize the Surface and Back Contact in Kesterite Solar Cells.

The ambient air-processed preparation of kesterite Cu2 ZnSn(S,Se)4 (CZTSSe) thin film is highly promising for the fabrication of low-cost and eco-friendly solar cells. However, the Sn volatilization loss and formation of a thick Mo(S,Se)2 interfacial layer during the traditional selenization process pose challenges for fabricating high-efficiency CZTSSe solar cells. Here, CZTS precursors prepared by a sol-gel process in ambient air are selenized and assisted with SnSe2 vapor via one- and two-step selenization to prepare a CZTSSe absorber on a Mo film and, subsequently, solar cells. For one-step selenization, the thickness of the fine grain and Mo(S,Se)2 layers near the back contact can be significantly reduced with increasing SnSe2 vapor partial pressure in the mixed selenization atmosphere, while the device efficiency is only 7.97% due to the severe interface recombination. For two-step selenization, the desired morphology and stoichiometry of the absorber can be achieved through the assistance of Sn-poor precursors selenized with high SnSe2 vapor partial pressure to regulate the Sn content in CZTSSe, yielding the highest efficiency of 10.85%. This study improves the understanding of the key role of the microenvironment during film growth towards the production of high-efficiency thin film solar cells and other photoelectronic devices.

Numerical simulation and performance optimization of GeSe based thin film solar cell with NiO as back surface field layer

Germanium monoselenide (GeSe) has emerged as a viable candidate for absorber material in thin film solar cell (TFSC) due to its favorable material characteristics. Herein, the novel GeSe based TFSC with CdS as buffer layer and NiO as back surface field (BSF) layer has been proposed and its photovoltaic performance has been evaluated theoretically using wxAMPS software. The device output parameters have been assessed by varying thickness and carrier concentration for the GeSe layer, CdS layer and NiO layer, respectively. Moreover, the defect densities in GeSe absorber layer, CdS/GeSe and GeSe/NiO interface layers, and the work function of metal electrode at the cell rear side have been altered to evaluate the photovoltaic characteristics. Conversion efficiency of 31.37% has been obtained for the proposed GeSe-based TFSC with the new architecture under the conditions such as the thicknesses of the CdS layer, GeSe layer and NiO layer are optimized to be 0.03 μm, 0.3 μm and 0.05 μm, respectively; the carrier concentrations of the CdS layer, GeSe layer and NiO layer are optimized to be 1018 cm−3, 1019 cm−3 and 1020 cm−3, respectively; the defect densities in the GeSe layer, IDL1, IDL2 both are set to be 1015 cm−3. These results suggest that GeSe can be employed as the promising absorber layer to fabricate low-cost and high efficiency TFSC.

Synthesis of titanium-doped CdIn2S4 thin film and its photoelectric properties for intermediate band solar cells

The series Titanium-doped CdIn2S4 (Ti-CIS) thin films, with a spinel structure, were successfully synthesized by a typical technology of magnetron sputtering. The prepared Ti-CIS thin films were characterized by X-ray diffraction patterns, Raman spectrometer, energy dispersive X-ray analysis, transient photocurrent response and UV–vis–NIR spectrophotometer. The experimental results demonstrated that the optical absorption spectra were widened in Ti-CIS films. Due to Ti doping, two additional sub-band edge responses were observed at about 760 nm (1.63 eV) and 1150 nm (1.07 eV), which indicated a partially filled intermediate band (IB) was formed in the forbidden band of Ti-CGS3 film by the spin-up t2 g states, and leaded to lower-energy photon absorption. Whereas, no additional sub-band edge responses were obviously observed in the optical absorption spectra of the Ti-CIS1 and Ti-CIS2 films, probably because of the Ti-CIS films inferior in quality or less doped-Ti content. The result analysis of the transient photocurrent response further verified that a larger number of carriers are generated in the Ti-CIS films, the surface recombination process rarely occurs. In general, the good photoelectric properties of Ti-CIS films prepared by magnetron sputtering expected to be a promising candidate IB material for the high-efficiency thin film solar cells.

Exploring a high-carrier-mobility black phosphorus/MoSe2 heterostructure for high-efficiency thin film solar cells

Transition metal dichalcogenides (TMDCs) with self-passivated surfaces, suitable bandgaps and high optical-absorption coefficients are very promising for thin film solar cells, but seriously hindered by low carrier mobility. Herein, we propose interface-engineered two-dimensional van der Waals heterostructure composed of high-carrier-mobility black phosphorus (BP) layer and MoSe2 layer, and demonstrate a new-type BP/MoSe2 heterostructure thin film solar cell with high efficiency. The electronic structure and optical properties of both BP/MoSe2 and BP/MoS2 heterostructures are systematically investigated. Compared with BP/MoS2 heterostructure, BP/MoSe2 heterostructure shows enhanced photoelectric characteristics. Additionally, BP/MoSe2 heterostructure has greater light absorption intensity as well as a wider absorption range, achieving a much higher power conversion efficiency of up to 23.04%. It is found that the built-in electric field at the interface of BP/MoSe2 heterostructure accelerates the separation of electron-hole pairs. This work provides a feasible strategy for using the BP/MoSe2 heterostructure for next-generation high-specific-power thin film solar cells.

Influence of Mo-pretreating on microstructure evolution of solution-processed absorbers for high efficient CZTSSe solar cells

For Mo-based Cu2ZnSn(S,Se)4 (CZTSSe) thin-film solar cells, high quality CZTSSe absorbers together with a moderately thick MoSe2 layer at CZTSSe/Mo interfaces are crucial for boosting the cell efficiency. Herein, a simple Mo pretreating method is proposed and its influence on microstructure evolution of solution-processed CZTSSe absorbers under different selenization temperatures is detailedly investigated. It is found that Mo pretreatment can not only significantly affect the microstructure formation of CZTSSe film but also suppress the over-selenization of Mo electrode, and effectively promote the cell efficiency from 2.48% to 6.67% by combing an optimized selenization process. The results are of great significance for the optimization of absorber layer structures in high-efficient CZTSSe thin-film solar cells.

Cadmium sulphide thin films deposition and characterization for device applications

Thin films of metal chalcogenides (sulphides, selenides, and tellurides) are investigated, and group II-VI semiconducting materials are more attracted to the thin films, and researchers are more interested in group II-VI semiconducting materials because of their use in photovoltaic cells, photoconductors, optical filters, solar cells, sensors, and other optoelectronic devices. Cadmium sulphide is a semiconducting material that corresponds to the II-VI family and has an energy bandgap of 2.42 eV. It is significant because of their numerous applications in optoelectronic devices, solar cells, LEDs, photoconductors, and other fields. It's also beneficial for window layers in CdTe or CuInSe2-based high-efficiency thin-film solar cells. It can be prepared by several techniques like chemical bath deposition (CBD), electrodeposition, thermal evaporation, spray pyrolysis, molecular beam epitaxy, etc. We have prepared CdS thin films over Molybdenum substrate using a non-aqueous medium by the CBD method. The electrolyte was made by combining the AR grade of cadmium acetate (0.24 M) dissolved with ethylene glycol and ethanol (ratio = 1:2) and the electrolyte temperature was kept at 130 °C with 220 rpm. Molybdenum substrate was dipped into the electrolyte using rigid support and thiourea (0.35 M) was influenced by the prepared electrolyte. The film was deposited for 20 min, and the deposited films was found to be well adherent to the substrate and free of voids, pinholes, and pits. XRD, FESEM, EDS, AFM, and FTIR were used to see into the solid-state features of the films which have been deposited. The deposited film shows a significant peak at 2θ = 26.240 with the (002) plane, suggesting that the film has a crystalline hexagonal structure. Using AFM, RMS roughness value is equal to 92 nm. Compositional analysis peaks reveal the availability of Cd and S.

Simulating the performance of a high-efficiency SnS-based dual-heterojunction thin film solar cell

This article demonstrates a novel high efficiency ZnS/SnS/MoS2 dual-heterojunction thin film solar cell. The device has been optimized with respect to the thickness, doping concentration, and defect density of each constituent layer including working temperature and back contact metal work function using SCAPS-1D simulator. The MoS2 plays a promising role to serve as a back surface field (BSF) layer with commendatory band alignment, which provides an opportunity for higher absorption of longer wavelength photons utilizing the tail-states-assisted (TSA) two-step photon upconversion approach. The insertion of MoS2 in the ZnS/SnS pristine structure offers a significant improvement of the power conversion efficiency (PCE) within the detailed-balance limit with a rise from 20.1 to 41.4% with VOC of 0.91 V, JSC of 53.4 mA/cm2 and FF of 84.9%, respectively. This result reveals MoS2 as an effective BSF for low cost, highly efficient dual-heterojunction structure for future fabrication.

Chemical and Electrical Instability of MgxZn1−xO in CdTe Thin Film Solar Cell

Mg <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-</sub> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> O (MZO) is a promising window material for high-efficiency CdTe thin film solar cell fabrication. However, the performance of MZO-based CdTe solar cell exhibits high sensitivity to the heat treatment of MZO during device fabrication process. In this article, the chemical, microstructural and electrical instability of MZO films and their effect on device performance of CdTe thin film solar cell was studied. It is found that during the high-temperature vacuum treatment (400°C-600°C), the atomic element losses in the MZO films led to high oxygen-vacancy concentration and formation of an Mg-rich surface layer. The high-temperature treated MZO films exhibited rough surface morphology, high electronic conductivity, and low electron affinity. The rough MZO surface induced formation of trap states with high concentration in the CdTe absorber and decreased open-circuit voltage for the solar cell. The MZO conductivity and the surface electron affinity affect the carrier transport in the solar cells. This work demonstrates that the heat treatment process of the MZO window layer significantly affects the performance and reproducibility of CdTe solar cell fabrication.