Thin Film Heterojunction Solar Cells Research Articles

Benefits of Low Electron-Affinity Material as the N-Type Layer for Cu(In,Ga)S2 Solar Cell

Despite the potential in single- and multi-junction solar cells application, research into the wide band gap CuIn1−xGax(Se1−ySy)2 or CIG(SSe)2 solar cell material, with Eg≥1.5eV, has yet to be extensively performed to date. In this work, we conducted a numerical study into the role of the n-type layers in CIG(SSe)2 heterojunction solar cells, specifically concerning the maximum open-circuit voltage of the devices. In the first part of the study, we derived a new ideal open-circuit voltage equation for a thin-film heterojunction solar cell by taking into account the current contribution from the depletion region. The accuracy of the new equation was validated through a simulation model in the second part of the study. Another simulation model was also used to clarify the design rules of the n-type layer in a wide band gap CIG(SSe)2 solar cell. Our work stressed the importance of a positive conduction band offset on the n-/p-type interface, through the use of a low electron affinity n-type material for a solar cell with a high open-circuit voltage. Through a precise selection of the window layer material, a buffer-free CIG(SSe)2 design is sufficient to fulfill such conditions. We also proposed the specific roles of the n-type layer, i.e., as a passivation layer and selective electron contact, in the operation of CIGS2 solar cells.

Numerical modeling of copper indium disulfide thin film based solar cells

In this work we have modeled CuInS 2 based solar cells. CuInS 2 is a p-type semiconductor which is used as an absorber layer in the heterojunction thin film solar cell ZnO:Al/i-ZnO/CdS/CuInS 2 /Mo. Numerical modeling was done by SCAPS-1D. The simulation focuses on studying several effects on photovoltaic parameters; open circuit voltage, density of short circuit, fill factor and efficiency. In a first step we have studied temperature effect; the performance of the cell decreased because of the decrease of open circuit voltage due to the rise of reverse current, in the other hand the fill factor increases at high temperature which is the same behavior of Silicon based solar cells. Thickness of the absorber layer has been varied too, 2.5 μm of thickness is the optimum value chosen instead of higher thickness in order to have a compromise between cost and efficiency. After that we decided to design a Cadmium free cell by replacing Cadmium Sulfide (CdS) layer with Tin Disulfide (SnS 2 ). However, cadmium layer showed better efficiency than SnS 2 . Then we discussed the importance of back surface field layer (Cu 2 O), whom insertion leads to improve the efficiency to 22.73% compared to the efficiency obtained by the conventional structure 12.64%. • New structures ZnO:Al/i-ZnO/CdS/CuInS 2 /Cu 2 O/Mo and ZnO:Al/i-ZnO/SnS 2 /CuInS 2 /Cu 2 O/Mo have been modeled. • The ZnO:Al/i-ZnO/CdS/CuInS 2 /Cu 2 O/Mo showed a good stability under temperature varied from 300 K to 325 K. • An efficiency of 22.73% have been achieved with ZnO:Al/i-ZnO/CdS/CuInS 2 /Cu 2 O/Mo. • The Cadmium free structure ZnO:Al/i-ZnO/SnS 2 /CuInS 2 /Cu 2 O/Mo showed an efficiency of 21.62%.

Numerical study of semi-transparent thin film heterojunction p-CuO/nZnO/AZO/ITO solar cells device model using SCAPS-1D

In the current time, transparent and semitransparent solar cells in photovoltaic industry have drawn important attention owing to their potential use as solar windows, and energy harvesting devices for building, vehicle integration and flexible electronics. In this work, a semitransparent thin film heterojunction solar cells device structure of p-CuO/nZnO/AZO/ITO was numerically modeled using SCAPS-1D software tools. The cell’s performance was investigated in terms of the different material layer properties, such as the thickness and carrier concentration or doping level. The simulation results of copper based semi-transparent thin film solar cell (TFSC) as the bottom cell model indicates that the highest efficiency was achieved at 8.9116 %, with the thickness and carrier concentration of n-ZnO material layer set at 20 nm, and 5.0 x 1018 cm-3 respectively, whereas the thickness of CuO absorber layer was fixed at 110 nm. Finally, the overall results show that CuO based absorber layer exhibits potential as photoactive material particularly for semitransparent thin film solar cells applications.

Photovoltaic performance enhancement in CdTe thin-film heterojunction solar cell with Sb2S3 as hole transport layer

In this work, we design a novel cadmium telluride (CdTe)-based solar structure with antimony sulfide (Sb2S3) as hole transport layer (HTL). One Dimensional Solar Cell Capacitance Simulator (SCAPS-1D) program is used to perform comparison studies on the photovoltaic performances between the standard thin-film cadmium sulfide (CdS)/CdTe solar cell and the proposed Al/FTO/CdS/CdTe/Sb2S3/Ni heterojunction structure. The solar cell outputs such as open-circuit voltage (Voc), short-circuit current density (Jsc), fill-factor (FF), and efficiency have been evaluated by varying impacts of thickness, electron affinity, carrier concentration, and bulk defect density of different layers. In addition, we have analyzed the effect of interface defects at both CdS/CdTe and CdTe/Sb2S3 interfaces. This study reveals that the introduction of Sb2S3 as HTL improves the Voc appreciably by creating appropriate band alignment with the CdTe absorber and thus remarkably enhance the efficiency of solar cell by lowering carrier recombination at back contact surface. Moreover, the impacts of working temperature, back contact metal work function, and surface recombination velocity are elucidated. The absorber thickness is optimized to be 1.0 µm with doping concentration of 2.1 × 1015 cm−3. Best efficiency of 28.41% together with other parameters such as Voc of 1.15 V, Jsc of 28.74 mA/cm2, and FF of 86.03% is achieved for the optimized device. These results lead to suggest that the Sb2S3 as HTL can be employed to fabricate highly efficient and inexpensive thin-film CdTe heterojunction solar devices.

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.

Effect of intrinsic ZnO thickness on the performance of SnS/CdS-based thin-film solar cells

Tin monosulfide (SnS) has promising properties as an absorber material for thin-film solar cells (TFSCs). SnS/CdS-based TFSCs have the following device structure: SLG/Mo/SnS/CdS/i-ZnO/AZO/Al. The optimization of thickness of intrinsic zinc oxide (i-ZnO) for SnS-absorber layers and its impact on SnS/CdS heterojunction TFSCs has been investigated at different thicknesses ranging from 39 nm to 73 nm. With the increase in thickness of i-ZnO from 39 nm to 45 nm, the overall performance improved. The highest PCE of 3.50% (with VOC of 0.334 V, JSC of 18.9 mA cm−2, and FF of 55.5%) was observed for 45 nm-thick i-ZnO layers. Upon a further increase in the i-ZnO thickness to 73 nm, the device performance deteriorated, indicating that the optimum thickness of the i-ZnO is 45 nm. The device performances were analyzed comprehensively for different i-ZnO thicknesses.

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.

Effect of substrate temperature on the growth of CuSbS2 thin films by chemical spray pyrolysis

CuSbS2 is an emerging potential compound semiconductor for absorber layer in thin film heterojunction solar cell. Spray pyrolysis technique has been successfully employed to deposit CuSbS2 thin films onto soda-lime glass substrates held at different substrate temperatures in the range of 220 °C–280 °C. The structural and optical analysis revealed that films deposited at 260 °C are CuSbS2 with chalcostibite structure. The films deposited at other substrate temperatures contained binary/ternary phases like Cu2-xS, Cu3SbS4 and Cu12Sb4S13. The lattice parameters of CuSbS2 films are found to be a = 0.599 nm, b = 0.379 nm and c = 1.449 nm respectively. The band gap of CuSbS2 films is close to the optimum band gap (1.5eV) required for highest theoretical photovoltaic conversion efficiency. The optical absorption coefficient value lies in the range of 104 cm−1. The nature of these films is found to be p-type.

Simulating the performance of a highly efficient CuBi2O4-based thin-film solar cell

In this study, copper bismuth oxide (CuBi2O4) absorber-based thin film heterojunction solar cell structure consisting of Al/FTO/CdS/CuBi2O4/Ni has been proposed. The proposed solar cell device structure has been modeled and analyzed by using the solar cell capacitance simulator in one dimension (SCAPS-1D) software program. The performance of the proposed photovoltaic device is evaluated numerically by varying thickness, doping concentrations, defect density, operating temperature, back metal contact work function, series and shunt resistances. The current density–voltage behaviors at dark and under illumination are investigated. To realize the high efficiency CuBi2O4-based solar cell, the thickness, acceptor and donor densities, defect densities of different layers have been optimized. The present work reveals that the power conversion efficiency can be enhanced by increasing the absorber layer thickness. The efficiency of 26.0% with open-circuit voltage of 0.97 V, short-circuit current density of 31.61 mA/cm2, and fill-factor of 84.58% is achieved for the proposed solar cell at the optimum 2.0-μm-thick CuBi2O4 absorber layer. It is suggested that the p-type CuBi2O4 material proposed in the present study can be employed as a promising absorber layer for applications in the low cost and high efficiency thin-film solar cells.

Влияние параметров кристаллической подложки на максимальную мощность кремниевых гетеропереходных солнечных элементов

The effect of the donor impurity concentration and the lifetime of charge carriers in a crystalline silicon substrate on the maximum power of heterojunction thin-film solar cells is studied. The model used in the calculations takes into account the features of photocurrent generation under conditions of medium or high levels of injection of charge carriers at an arbitrary ratio between the diffusion length and the thickness of the semiconductor wafer. The proposed technique makes it possible, with sufficient accuracy for practical purposes, to calculate the permissible variation limits of the substrate parameters, which ensure the specified values of the performance characteristics of photoelectric converters.

Defect states and grading induced bandgap variability analysis of CIGS solar cells through device simulations

Copper-indium-gallium-diselenide (CIGS) is one of the promising absorbing material in thin film solar cells. It is a direct band gap material with the band gap (Eg) ranging from 0.98 to 1.68 eV. The band gap of this material is dependent on the composition of the material. The band gap enhancement leads to significant reduction in the extent of exciton recombination but on the other hand it also reduces the absorption in the absorber layer. We simulated and analyzed the effect of band gap variations in CIGS layer, induced by grading of doping concentration profile and defect states over the performance of solar cell. The performance analysis has been done using SCAPS-1D (Solar Cell Capacitance Simulator) simulator. It is intended to develop specially to simulate the AC and DC characteristics of hetero-junction thin film solar cells, especially CIGS and CdTe solar cells. By the introduction of grading in the CIGS material, an enhancement of 2.48% has been observed in the overall efficiency. This enhancement can be attributed to the reduction in recombination and increase in the exciton generation.

Numerically investigating the AZO/Cu2O heterojunction solar cell using ZnO/CdS buffer layer

Aluminium (Al)-doped zinc oxide (ZnO)/copper oxide (AZO/Cu2O) heterojunction solar cell is analyzed by a 1-D solar cell capacitance simulator (SCAPS-1D). The influence of single (CdS) and double (ZnO and CdS) buffer layers on the performance of AZO/Cu2O heterojunction solar cells is studied. The effects of device parameters such as Cu2O acceptor and CdS donor doping concentrations, external quantum efficiency, interface states density, metal work function, absorber and buffer layer thicknesses, and working temperature on both single and double buffer layer solar cell are carried out. The optimized solar cell structure of single buffer AZO/CdS/Cu2O/Au and double buffer AZO/ZnO/CdS/Cu2O/Au results in the power conversion efficiency (PCE) of 10.47 and 10.60 %, short circuit current density (JSC) of 11.33 and 11.37 mA cm−2, open-circuit voltage (Voc) of 1.1381 and 1.1405 V and fill factor (FF) of 81.21 and 81.74 %, respectively under illumination. Our findings reveal that the PCE of AZO/Cu2O based heterojunction thin-film solar cell is enhanced through the usage of a double buffer (ZnO/CdS) layer in comparison to the single (CdS) buffer layer.

Tuning the properties of RF sputtered tin sulphide thin films and enhanced performance in RF sputtered SnS thin films hetero-junction solar cell devices

Abstract Tin sulphide (SnS) thin films were grown using the RF sputtering techniques. The working pressures (WP) were tuned between 0.70 and 4.00 Pa at fixed RF power of 100 W and deposition time of 2 min. X-ray diffractometry studies indicate that the films crystallized in the orthorhombic crystal structure and were single phase. The crystallite size increased up to a critical working pressure of 1.33 Pa and decreased thereafter with increased WP. Scanning electron microscopy (SEM) indicates that the films exhibit columnar grain structures. Energy dispersive spectroscopy indicates that the films are slightly Sn-rich. Transmittance and reflectance plots exhibits interference pattern, an indication that the films were of uniform thickness. Analysis from the optical data gives optical absorption coefficient (α) > 104 cm−1, and direct energy bandgap that exhibits relative decrease with the deposition conditions. Electrical studies from Hall effect measurements indicates that the films possess p-type electrical conductivity, and carrier concentration of 1016 cm−3 for films grown at WP of 1.33 Pa. The RF sputtered SnS thin films grown on Mo-substrates served as absorber layers to fabricate thin film hetero-junction solar cell devices in the substrate configuration with a cadmium sulphide (CdS) window partner. The best device yielded a short circuit current density of 25.94 mA/cm2, open circuit voltage of 0.087 V and an enhanced solar conversion efficiency of 0.60%. A world record value for RF-sputtered SnS/CdS based hetero-junction thin film solar cell devices.

EFFECT OF TIN PRECURSORS ON THE DEPOSITION OF Cu2ZnSnS4 THIN FILMS

Cu2ZnSnS4 is a potential compound semiconducting material for solar absorber layer in thin film heterojunction solar cells. Chemical spray pyrolysis technique has been successfully employed to deposit these thin films using two different tin precursors. Thin films were characterized by studying their structural, composition, electrical and optical properties. X-ray diffraction pattern reveals that these films exhibit polycrystalline nature with kesterite structure. Lattice parameters of Cu2ZnSnS4 films are found to be a = b = 0.544 nm and c = 1.084 nm. Optical band gap, evaluated from spectral transmittance data, is close to ideal energy gap (1.5 eV) exhibit highest conversion efficiency. Optical absorption coefficient of these films is ≥ 104 cm-1 . These films exhibit p-type nature. A humble attempt is made to fabricate a typical heterojunction Cu2ZnSnS4 thin film solar cell.

Influence of deposition time and annealing treatments on the properties of chemically deposited Sn2Sb2S5 thin films and photovoltaic behavior of Sn2Sb2S5-based solar cells

Abstract Thin films of chemical bath deposited tin antimony sulphide (Sn2Sb2S5) were tuned by varying the deposition time between 1 and 3 h, and postdeposition heat treatments. The films were grown on soda lime glass (SLG) and on molybdenum glass (Mo-SLG) substrates, respectively. The film thickness increased with deposition time up to 2 h and decreased thereafter. Structural analysis from X-ray diffractometry showed that the films were single phase. This was corroborated by X-ray photoelectron spectroscopy (XPS) analysis. Energy-dispersive spectroscopy results give antimony/sulphur (Sb/S) ratio and antimony/tin (Sb/Sn) ratio that increased with deposition time in the SLG substrates only. Optical constants extracted from optical spectroscopy measurements give optical absorption coefficient (α) > 104 cm−1, and direct energy bandgap with values in the range 1.30 to 1.48 eV. The Hall effect measurements performed on films grown on the SLG substrates indicated that the films were p-type electrical conductivity with electrical resistivity in the range 103 to 104 Ωcm. The films grown on the Mo-SLG served as absorber layers to fabricate thin film heterojunction solar cell devices in the substrate configuration with a cadmium sulphide (CdS) window partner. The best device yielded a short-circuit current density of 20 mA/cm2, open-circuit voltage of 0.012 V and a solar conversion efficiency of 0.04%.

Effects of Mg% on open circuit voltage and short circuit current density of Zn1-xMgxO/Cu2O heterojunction thin film solar cells, processed using electrochemical deposition and spin coating

Zn1-xMgxO/Cu2O/Ag solar cells were fabricated upon fluorine doped tin oxide coated soda lime glass substrate with varying percentage of Mg mol% doping in zinc oxide (ZnO) layer. Short circuit current density & open circuit voltages of the fabricated cells were investigated. Optimum doping with Mg improved the transparency of ZnO layer which helped in increasing the short circuit current density of solar cells. An enhancement of open circuit voltage was observed with increase in x, which was investigated using X-ray photoelectron spectroscopy and the results revealed that with increase in x, there was a decrease in conduction band offset between Zn1-xMgxO and cuprous oxide layers. From UV-Visible transmittance spectra, it was observed that with Mg doping in ZnO nanostructure, optical losses were reduced which resulted in increase in Short circuit current density. The objective of this study was to investigate and develop a technology for fabrication of solar cells that is both cost effective and easy to produce.

Electrodeposition and Characterization of CdTe thin films for photovoltaic applications

Cadmium Telluride (CdTe) is direct band gap semiconductor, ∼ 1.45 eV at room temperature. It is one of the promising absorber materials for heterojunction thin film solar cell application due to high absorption coefficient and less carrier diffusion length. We have electrodeposited CdTe thin film using conventional three-electrode geometry onto FTO coated glass substrate from non-aqueous electrolyte at potential −0.625 V. As-prepared samples of CdTe were characterized thoroughly to study structural, optical, morphological, compositional and transport properties. The films were polycrystalline in nature with mixed cubic and hexagonal crystal structure without metallic phases. Highly crystalline, large grain, compact CdTe thin films have been obtained without post-deposition heat treatment. The calculated electrical parameter can be further improved upon post-deposition thermal heat treatment and/or chemical surface treatment to produce high efficiency thin film solar cell devices. The reported growth procedure could be suitable for development of flexible thin film solar cells devices on to plastic substrates.

Development of a novel CdTe/ZnS/ZnTe heterojunction thin-film solar cells: a numerical approach

A novel heterojunction structure of cadmium telluride (CdTe)/zinc sulfide (ZnS)/zinc telluride (ZnTe) for thin-film solar cell (TFSC) applications was investigated numerically by Solar Cell Capacitance Simulator in One Dimension (SCAPS-1D). We made a comparative study on the performance of single-layer of Si/CdTe and multi-layers of Si/CdTe/ZnS/ZnTe structures. The optimum values for the thicknesses of CdTe absorber, ZnS, and ZnTe layers in the cell were found to be 2500, 40, and 80 nm, respectively. In the present work, the conversion efficiency (η) of 21.38% was obtained with open-circuit voltage, Voc = 1.01 V, short-circuit current density, Jsc = 29.32 mA cm−2, and fill-factor, FF = 72.06% in case of multi-layer structure with antireflection coatings (ARCs). The simulation results suggest that the ARC layers presented in this study would be effective to fabricate the high-efficiency solar cells.

Band offset engineering for p-SnO/n-mc-Si heterojunction solar cell

A cost-effective p-SnOx/n-multicrystalline Si heterojunction thin film solar cell with SnOx as an absorber layer is investigated by Technology Computer-Aided Design simulation using experimental values of the absorption coefficient of the SnOx-layer. Heterointerface recombination and trapping of carriers due to the band offsets are considered in the simulation. Conduction and valence band offsets, which can be engineered by varying the growth kinetics dependent bandgap and electron affinity of SnOx, play a significant role in enhancing the efficiency of the solar cell. A maximum conversion efficiency of 10.506% is obtained by a proper choice of affinity and bandgap for a particular thickness of the SnOx-layer.

ОПРЕДЕЛЕНИЕ ТЕХНОЛОГИИ И УСЛОВИЙ ИЗГОТОВЛЕНИЯ ГЕТЕРО СТРУКТУРНЫХ ТОНКОПЛЕНОЧНЫХ СОЛНЕЧНЫХ ЭЛЕМЕНТОВ

The paper presents the results of research on the most advanced technology for manufacturing semiconductor photovoltaic energy converters. Methods of manufacturing and research of thin-film heterojunction solar cells based on p-type silicon are analyzed. The materials of the initial components and the structure of the thin-film solar cell were selected. According to the results of the developed technology for obtaining a high-efficiency Converter with a base layer of p-type by sputtering on a vacuum magnetron machine with accelerated heat treatment, ways to improve the performance of solar cells are indicated. The main requirements for the production of the most efficient photovoltaic converters are explained. The electrophysical properties of semiconductors were used as the basis for the material selection criteria