Efficient Thin Film Solar Cells Research Articles

Growth and Fabrication of GaAs Thin-Film Solar Cells on a Si Substrate via Hetero Epitaxial Lift-Off

We demonstrate, for the first time, GaAs thin film solar cells epitaxially grown on a Si substrate using a metal wafer bonding and epitaxial lift-off process. A relatively thin 2.1 μm GaAs buffer layer was first grown on Si as a virtual substrate, and a threading dislocation density of 1.8 × 107 cm−2 was achieved via two In0.1Ga0.9As strained insertion layers and 6× thermal cycle annealing. An inverted p-on-n GaAs solar cell structure grown on the GaAs/Si virtual substrate showed homogenous photoluminescence peak intensities throughout the 2″ wafer. We show a 10.6% efficient GaAs thin film solar cell without anti-reflection coatings and compare it to nominally identical upright structure solar cells grown on GaAs and Si. This work paves the way for large-scale and low-cost wafer-bonded III-V multi-junction solar cells.

Highly efficient light trapping of clustered silicon nanowires for solar cell applications.

Due to their excellent photoelectric performance, nanostructures have attracted considerable attention in research to improve the power conversion efficiency of thin-film solar cells (TFSCs). Furthermore, cylindrical silicon nanowires (Cy-SiNWs) are regarded as promising candidates for a new generation of TFSCs. On this basis, many new nanostructures derived from conventional Cy-SiNWs have been studied extensively, but most of these structures require high manufacturing accuracy because of their complex morphology. In this paper, an ingenious design of clustered silicon nanowires (Cl-SiNWs) is introduced, whose cross section is similar to the flower shape and consists of four arcs with the same radius. Hence, it requires lower manufacturing difficulty compared with nanostructures with curvature variation of the cross-section profile (i.e., elliptic shape, crescent shape, etc.). In this study, the optical and electrical characterizations are numerically investigated using the finite-difference time-domain method. The numerical simulation shows that the optimized Cl-SiNWs achieve an optical ultimate efficiency (ηul) and circuit current density (Jsc) of 33.66% and 27.54mA/cm2, respectively, with an enhancement of 7.3% over conventional Cy-SiNWs. Further, the ηul and Jsc improve to 42.20% and 34.53mA/cm2 by adding the silicon substrate and silver backreflector. More importantly, the ηul of Cl-SiNWs always obtained a higher value than Cy-SiNWs at a recommended diameter range of 360-560 nm. Therefore, the suggested Cl-SiNWs have exhibited tremendous potential for the future development of low-cost and highly efficient solar cells.

Quasi-hemispherical pit array textured surface for increasing the efficiency of thin-film solar cells

Enhancing light absorption is an important way for solar cells to increase the conversion efficiency. In this paper, we prepared a quasi-hemispherical pit array texture on the glass surface through the micro-fabrication process. Then, silicon thin-film (a-Si:H) solar cells were deposited on the other smooth surface. Pit array textured cells exhibit a higher short-circuit current density and power conversion efficiency than flat devices by ∼7% and 5%, respectively. The reflectance spectrum of textured solar cells is considerably reduced, and the external quantum efficiency is considerably improved in the 300–800 nm wavelength range. Through COMSOL Multiphysics and finite-difference time-domain (FDTD) simulation, three significant effects identify light-trapping characteristics for textured structures: surface reflection reduction, secondary absorption, and light scattering. As a result, the textured surface of the quasi-hemispherical pit array can considerably increase the efficiency of solar cells. Meanwhile, the Lumerical DEVICE software was used to simulate the electrical characteristics of the cell, and the experimental results were theoretically proven.

Additive Strategy to Regulate Crystallization and Charge Carrier Dynamics of Csbi3i10 Towards Efficient and Stable Thin Film Solar Cells

Additive Strategy to Regulate Crystallization and Charge Carrier Dynamics of Csbi3i10 Towards Efficient and Stable Thin Film Solar Cells

Perovskite Solar Cells Go Bifacial-Mutual Benefits for Efficiency and Durability.

Bifacial solar cells hold the potential to achieve a higher power output per unit area than conventional monofacial devices without significantly increasing manufacturing costs. However, efficient bifacial designs are challenging to implement in inorganic thin-film solar cells because of their short carrier lifetimes and high rear surface recombination. The emergence of perovskite photovoltaic (PV) technology creates a golden opportunity to realize efficient bifacial thin-film solar cells, owing to their outstanding optoelectronic properties and unique features of device physics. More importantly, transparent conducting oxide electrodes can prevent electrode corrosion by halide ions, mitigating one major instability issue of the perovskite devices. Here, the theory of bifacial PV devices is summarized and the advantages of bifacial perovskite solar cells, such as high power output, enhanced device durability, and low economic and environmental costs, are reviewed. The limitations and challenges for bifacial perovskite solar cells are also discussed. Finally, the awareness of bifacial solar cells as a feasible commercialization pathway of perovskite PV for mainstream solar power generation and building-integrated PV is advocated and future research directions are suggested.

Novel perovskite solar cell with Distributed Bragg Reflector.

This paper reports numerical modeling of perovskite solar cell which has been knotted with Distributed Bragg Reflector pairs to extract high energy efficiency. The geometry of the proposed cells is simulated with three different kinds of perovskite materials including CH3NH3PbI3, CH3NH3PbBr3, and CH3NH3SnI3. The toxic perovskite material based on Lead iodide and lead bromide appears to be more efficient as compared to non-toxic perovskite material. The executed simulated photovoltaic parameters with the highest efficient structure are open circuit voltage = 1.409 (V), short circuit current density = 24.09 mA/cm2, fill factor = 86.18%, and efficiency = 24.38%. Moreover, a comparison of the current study with different kinds of structures has been made and surprisingly our novel geometry holds enhanced performance parameters that are featured with back reflector pairs (Si/SiO2). The applied numerical approach and presented designing effort of geometry are beneficial to obtain results that have the potential to address problems with less efficient thin-film solar cells.

Computational investigation on the photovoltaic performance of an efficient GeSe-based dual-heterojunction thin film solar cell

This article reports the design and computational analysis of an efficient GeSe-based n-ZnSe/p-GeSe/p +-WSe2 dual-heterojunction (DH) thin film solar cell using SCAPS-1D simulation program with physical parameters from the literature. The device has been optimized considering the thickness, doping and defect density of each layer. The optimized device shows an efficiency of ∼42.18% with a short circuit current density, J SC of 47.84 mA cm−2, an open circuit voltage, V OC of 1.07 V and fill factor, FF of 82.80%, respectively that remains within the Shockley-Queisser limit of a DH solar cell. The raised built-in potential developed between the two interfaces of the devices produces a surpassing V OC. The higher J SC is attributed to the current generated by absorption of sub-band gap photons by a tail-states-assisted two-step photon upconversion mechanism in the WSe2 back surface field layer. These results indicate the potential of manufacturing the high efficiency GeSe-based DH solar cell in future.

Design of a highly efficient FeS2-based dual-heterojunction thin film solar cell

ABSTRACT This article demonstrates a highly efficient FeS2-based n-ZnSe/p-FeS2/p+-AlxGa1-xSb dual-heterojunction thin film solar cell using SCAPS-1D simulator. The study has been carried out taking the physical parameters from the literature. The influence of thickness, doping, and defect concentration of ZnSe, FeS2, and AlxGa1-xSb layers on the photovoltaic performance of the solar cell has been investigated in details. The power conversion efficiency (PCE) of the n-ZnSe/p-FeS2 single-heterojunction solar cell is ~23.22% with JSC = 47.52 mA/cm2, VOC = 0.59 V, and FF = 82.62%, respectively. The PCE of the solar cell further increases to ~36.75% with JSC = 48.13 mA/cm2, VOC = 0.94 V, and FF = 80.75%, respectively with the insertion of AlxGa1-xSb back surface field (BSF) layer. This increase in PCE is mainly due to the enhancement of VOC which is resulted from the suitable band alignment of the dual-heterojunction devices. These results indicate that FeS2-based dual-heterojunction thin film solar cell with ZnSe and AlxGa1-xSb window and BSF layers, respectively, is a potential candidate to fabricate high efficiency thin film solar cell for harvesting solar energy in the future.

Enhanced efficiency of graded-bandgap thin-film solar cells due to concentrated sunlight.

A systematic study was performed with a coupled optoelectronic model to examine the effect of the concentration of sunlight on the efficiencies of CIGS, CZTSSe and AlGaAs thin-film solar cells with a graded-bandgap absorber layer. Efficiencies of 34.6% for CIGS thin-film solar cells and 29.9% for CZTSSe thin-film solar cells are predicted with a concentration of 100 suns, the respective one-sun efficiencies being 27.7% and 21.7%. An efficiency of 36.7% is predicted for AlGaAs thin-film solar cells with a concentration of 60 suns, in comparison to 34.5% one-sun efficiency. Sunlight concentration does not affect the per-sun electron-hole-pair (EHP) generation rate but reduces the per-sun EHP recombination rate either near the front and back faces or in the graded-bandgap regions of the absorber layer, depending upon the semiconductor used for that layer, and this is the primary reason for the improvement in efficiency. Other effects include the enhancement of open-circuit voltage, which can be positively correlated to the higher short-circuit current density. Sunlight concentration can therefore play a significant role in enhancing the efficiency of thin-film solar cells.

ZnO thickness and ZnTe back contact effect of CdTe thin film solar cell Voc and efficiency progression

CdTe thin film (TF) solar cells are most promising photovoltaic (PV) technology in commercial platform. Back contacts and interface defects related opto-electrical losses are still vital to limit its further technological benefit. TF PV cells shallow recombination and parasitic loss lessening purpose carrier selective back contact with band matching window layers are essential. Beside that back and front contact thickness choice is vital for field associated selective carrier collection and generous optical transmission into the active junction of the cell. It can make variation of cell efficiency. Window and front contact layers band edge variation and back contact thickness effect is analyzed by SCAPS-1D simulation software. ZnO and SnO2 front contact for CdS and CdSe window layers effect are numerically studied for 1 μm CdTe thin film PV cell. Significance of materials for front contact and its thickness effect on current density while ZnTe back surface field contact thickness effect on open circuit voltage and efficiency are demonstrated. Finally, ZnO/CdS/CdTe/ZnTe cell of 0.925 V open circuit voltage and 19.06% efficiency has been achieved for 90 nm of ZnTe with Molybdenum (Mo) back contact.

Efficiency enhancement of WSe2 heterojunction solar cell with CuSCN as a hole transport layer: A numerical simulation approach

In this research work, the tungsten diselenide (WSe2)-based thin-film solar cell with a copper thiocyanate (CuSCN) hole transport layer (HTL) has been designed and studied by using the Solar Cell Capacitance Simulator in One Dimension software program (SCAPS-1D). A comparative numerical study between Al/ITO/CdS/WSe2/Ni and Al/ITO/CdS/WSe2/CuSCN/Ni has been done. The SCAPS-1D simulator has been utilized to investigate photovoltaic parameters such as open circuit voltage, short-circuit current density, fill-factor, power conversion efficiency and quantum efficiency of heterojunction solar cell due to the variation of thickness, doping density, bulk defect density, defect density at buffer/absorber and absorber/HTL interfaces, operating temperature, band alignment and back surface recombination velocity. The conversion efficiency of 17.33% has been determined for the WSe2 solar cell without HTL. On the contrary, the efficiency of the proposed solar cell with CuSCN HTL has been found to be 24.20% at the optimal device structure. These numerical findings of the present study may therefore provide an intuitive approach to fabricate an economically feasible and highly efficient WSe2-based heterojunction thin-film solar cell.

Atomic Layer Deposition of Ultrathin ZnO Films for Hybrid Window Layers for Cu(Inx,Ga1-x)Se2 Solar Cells.

The efficiency of thin-film chalcogenide solar cells is dependent on their window layer thickness. However, the application of an ultrathin window layer is difficult because of the limited capability of the deposition process. This paper reports the use of atomic layer deposition (ALD) processes for fabrication of thin window layers for Cu(Inx,Ga1−x)Se2 (CIGS) thin-film solar cells, replacing conventional sputtering techniques. We fabricated a viable ultrathin 12 nm window layer on a CdS buffer layer from the uniform conformal coating provided by ALD. CIGS solar cells with an ALD ZnO window layer exhibited superior photovoltaic performances to those of cells with a sputtered intrinsic ZnO (i-ZnO) window layer. The short-circuit current of the former solar cells improved with the reduction in light loss caused by using a thinner ZnO window layer with a wider band gap. Ultrathin uniform A-ZnO window layers also proved more effective than sputtered i-ZnO layers at improving the open-circuit voltage of the CIGS solar cells, because of the additional buffering effect caused by their semiconducting nature. In addition, because of the precise control of the material structure provided by ALD, CIGS solar cells with A-ZnO window layers exhibited a narrow deviation of photovoltaic properties, advantageous for large-scale mass production purposes.

Performance analysis of tungsten disulfide (WS2) as an alternative buffer layer for CdTe solar cell through numerical modeling

The cadmium telluride (CdTe) solar cells are the most widely used high efficiency thin film solar cells that have shown stable performance over a long time. Although being a frontier in thin film technology, the performance of CdTe solar cells is setback by pinhole effects when thin CdS buffer layers are used in devices for compensating the spectral loss. To overcome this, generally, a highly resistive ZnO is used as window layer between the transparent conducting oxide (TCO) and the CdS layer. In this work, a single tungsten disulfide (WS2) is proposed to replace the bilayer window in conventional CdTe solar cells. The band discontinuities at two interfaces of the WS2 in the proposed structure (p-CdTe/n-WS2/n-ITO) are studied with varying defect state density. The performance parameters such as open circuit voltage, short circuit current, fill factor, and efficiency are observed respectively for different defect state densities of interfaces and the bulk layer of WS2. Comparison between the conventional CdTe structure and proposed structure shows that the CdTe solar cells with a single WS2 buffer layer can perform as efficiently as the one with CdS/ZnO bilayer.

The absorber and buffer layer thicknesses for CdTe/CdS based thin film solar cell efficiency at various operational temperatures

Cadmium telluride (CdTe)/cadmium sulfide (CdS) solar cell is a promising candidate for photovoltaic (PV) energy production, as fabrication costs are compared by silicon wafers. We include an analysis of CdTe/CdS solar cells while optimizing structural parameters. Solar cell capacitance simulator (SCAPS)-1D 3.3 software is used to analyze and develop energy-efficient. The impact of operating thermal efficiency on solar cells is highlighted in this article to explore the temperature dependence. PV parameters were calculated in the different absorber, buffer, and window layer thicknesses (CdTe, CdS, and SnO2). The effect of the thicknesses of the layers, and the fundamental characteristics of open-circuit voltage, fill factor, short circuit current, and solar energy conversion efficiency were studied. The results showed the thickness of the absorber and buffer layers could be optimized. The temperature had a major impact on the CdTe/CdS solar cells as well. The optimized solar cell has an efficiency performance of >14% when exposed to the AM1.5 G spectrum. CdTe 3000 nm, CdS 50 nm, SnO2 500 nm, and (at) T 300k were the I-V characteristics gave the best conversion open circuit voltage (Voc)=0.8317 volts, short circuit current density (Jsc)=23.15 mA/cm2, fill factor (FF)%=77.48, and efficiency (η)%=14.73. The results can be used to provide important guidance for future work on multi-junction solar cell design.

RGO@CuSCN bilayer as composite back contact for highly efficient CdTe thin-film solar cells

Highly efficient CdTe solar cells were fabricated by introducing [email protected] as a composite back contact. The [email protected] was prepared by convenient solution-processed method. As a Cu-doping source and electron reflection layer, CuSCN could facilitate to dope CdTe and decrease the carrier recombination on the back surface of CdTe. The rGO, as a hole transport layer, could suppress unfavorable over-diffusion of Cu and improve hole collection and transport. The results show the obvious reduction of back barrier height and decrease of the dark current density in the devices with [email protected] back contact. Using facile coating method and optimal thermal annealing for the preparation of [email protected] composite back contact, CdTe solar cell presented greatly enhanced photovoltaic performance (Eff: 16.84%, Voc: 841 mV, Jsc: 26.83 mA/cm2, FF: 74.6%).

Key factors governing the device performance of CIGS solar cells: Insights from machine learning

Cu(In1-x,Gax)Se2 (CIGS) solar cells are a kind of highly efficient thin film solar cells, further breakthrough in their device efficiency relies on the development of advanced methods and/or deep insights into the factors governing the device efficiency. Herein, we use the machine learning (ML) algorithms to explore the key factors governing the device performance of the CIGS solar cells and the underlying correlations. The datasets for ML are obtained from the experimental reports, which enables the results more referable for experimental optimization. Key factors governing the device performance are screened based on the correlation studies. The ML algorithms including linear regression, neural network, random forest (RF) and extreme gradient boosting are employed, among which RF performs best in predicting the efficiency of the CIGS solar cells with high accuracy (root mean square error of 0.9% and1.8%, Pearson coefficient r of 0.9 and 0.88 for validation and test sets, respectively). Furthermore, the factors and their optimal scales for high device efficiency are predicted, which provides essential guidance for experimental device optimization.

Solution-processed Cd-substituted CZTS nanocrystals for sensitized liquid junction solar cells

The Earth-abundant kesterite Cu2ZnSnS4 (CZTS) exhibits outstanding structural, optical, and electronic properties for a wide range of optoelectronic applications. However, the efficiency of CZTS thin-film solar cells is limited due to a range of factors, including electronic disorder, secondary phases, and the presence of anti-site defects, which is a key factor limiting the Voc. The complete substitution of Zn lattice sites in CZTS nanocrystals (NCs) with Cd atoms offers a promising approach to overcome several of these intrinsic limitations. Herein, we investigate the effects of substituting Cd2+ into Zn2+ lattice sites in CZTS NCs through a facile solution-based method. The structural, morphological, optoelectronic, and power conversion efficiencies (PCEs) of the NCs synthesized have been systematically characterized using various experimental techniques, and the results are corroborated by first-principles density functional theory (DFT) calculations. The successful substitution of Zn by Cd is demonstrated to induce a structural transformation from the kesterite phase to the stannite phase, which results in the bandgap reduction from 1.51 eV (kesterite) to 1.1 eV (stannite), which is closer to the optimum bandgap value for outdoor photovoltaic applications. Furthermore, the PCE of the novel Cd-substituted liquid junction solar cell underwent a four-fold increase, reaching 1.1%. These results highlight the importance of substitutional doping strategies in optimizing existing CZTS-based materials to achieve improved device characteristics.

Effects of Cu Precursor on the Performance of Efficient CdTe Solar Cells.

Copper (Cu) incorporation is a key process for fabricating efficient CdTe-based thin-film solar cells and has been used in CdTe-based solar cell module manufacturing. Here, we investigate the effects of different Cu precursors on the performance of CdTe-based thin-film solar cells by incorporating Cu using a metallic Cu source (evaporated Cu) and ionic Cu sources (solution-processed cuprous chloride (CuCl) and copper chloride (CuCl2)). We find that ionic Cu precursors offer much better control in Cu diffusion than the metallic Cu precursor, producing better front junction quality, lower back-barrier heights, and better bulk defect property. Finally, outperforming power conversion efficiencies of 17.2 and 17.5% are obtained for devices with cadmium sulfide and zinc magnesium oxide as the front window layers, respectively, which are among the highest reported CdTe solar cells efficiencies. Our results suggest that an ionic Cu precursor is preferred as the dopant to fabricate efficient CdTe thin-film solar cells and modules.

The effect of different surface plasmon polariton shapes on thin-film solar cell efficiency

The effects of surface plasmon polaritons (SPPs) on the efficiency, series resistance, and shunt resistance of thin-film Si solar cells are studied and analyzed in this work. Different SPP shapes and their effects on the optical and electrical properties and thereby the efficiency of thin-film solar cells are studied. Semiconductor and electromagnetic models are incorporated to study the electrical and optical behaviors of the thin-film solar cells, respectively, using COMSOL Multiphysics three-dimensional (3D) numerical simulation software. An efficiency of 14.76% is achieved for triangular SPPs, representing a 1.07% improvement compared with SPP-free solar cells. The solar cell electrical parameters are also extracted based on a single-diode equivalent model. The series resistance is decreased by 3% for solar cells having equilateral-triangle SPPs compared with SPP-free solar cells.

Numerical investigation on performance improvement of WS2 thin-film solar cell with copper iodide as hole transport layer

In the present work, device modeling of tungsten disulfide-based thin-film solar cell with copper iodide as hole transport layer has been performed using the Solar Cell Capacitance Simulator in One Dimension software program (SCAPS-1D). The SCAPS-1D simulator is also utilized to investigate the photovoltaic performances of tungsten disulfide (WS2)-based solar cells. This numerical study provides a comparison of the performances between the reference WS2-based solar cell structure without hole transport layer (HTL) consisting of Al/FTO/CdS/WS2/Ni and the proposed configuration of Al/FTO/CdS/WS2/CuI/Ni. The influences of thickness, doping density, bulk defect density, defect density at buffer/absorber and absorber/HTL interfaces, operating temperature, series and shunt resistances, and back surface recombination velocity on the solar cell output parameters have also been analyzed. It is revealed that the carrier recombination at the back side has notable effects on the overall photovoltaic performances of the WS2 heterojunction solar cell without HTL. The carrier recombination loss at the back surface can be reduced by incorporation of an ultra-thin 0.1 μm copper iodide (CuI) HTL into the reference WS2-based solar cell and thus improves the overall performances of the proposed photovoltaic device. The conversion efficiency of 22.09% has been found for the reference WS2 solar cell without HTL. On the other hand, the efficiency of the proposed solar cell with CuI HTL has been obtained to be 29.87% at the optimized device structure. Therefore, these findings may contribute insightful approach to fabricate viable, inexpensive, and highly efficient heterojunction thin-film solar cell.