Cadmium Sulfide Buffer Research Articles

Photovoltaic performance of magnetron sputtered antimony selenide thin film solar cells buffered by cadmium sulfide and cadmium sulfide /zinc sulfide

Antimony selenide (Sb2Se3)-based thin-film solar cells have recently attracted worldwide attention as an abundant, low-cost, and efficient photovoltaic technology. The highest efficiencies recorded for Sb2Se3 solar cells have been obtained using cadmium sulfide (CdS) as a buffer layer. The Cd-included hybrid buffer layers could be one option to increase device efficiency through more effective usage of light. Therefore, in this work, the effect of single CdS and hybrid CdS/zinc sulfide (ZnS) buffer layers on the photovoltaic performance of Sb2Se3 thin-film solar cells has been investigated in detail. Sb2Se3 thin films have been deposited on molybdenum (Mo)-coated soda-lime glass (SLG) substrates by radio frequency magnetron sputtering technique followed by a post-heat treatment process. The morphological, and structural properties of Sb2Se3 thin films have been investigated by X-Ray Diffraction and Scanning Electron Microscopy. To compare the device performances of single CdS and hybrid CdS/ZnS buffered Sb2Se3 thin-film solar cells, SLG/Mo/Sb2Se3/CdS/ZnS/indium tin oxide (ITO) and SLG/Mo/Sb2Se3/CdS/ITO structures have been fabricated. The findings of this study have revealed a reduction in solar cells’ performance from η=3.93% for CdS buffer to η=0.13% for CdS/ZnS hybrid buffer. The change in the solar cell performance using the CdS/ZnS hybrid buffer has been discussed in detail.

Novel Mg- and Ga-doped ZnO/Li-Doped Graphene Oxide Transparent Electrode/Electron-Transporting Layer Combinations for High-Performance Thin-Film Solar Cells.

Herein, a novel combination of Mg- and Ga-co-doped ZnO (MGZO)/Li-doped graphene oxide (LGO) transparent electrode (TE)/electron-transporting layer (ETL) has been applied for the first time in Cu2 ZnSn(S,Se)4 (CZTSSe) thin-film solar cells (TFSCs). MGZO has a wide optical spectrum with high transmittance compared to that with conventional Al-doped ZnO (AZO), enabling additional photon harvesting, and has a low electrical resistance that increases electron collection rate. These excellent optoelectronic properties significantly improved the short-circuit current density and fill factor of the TFSCs. Additionally, the solution-processable alternative LGO ETL prevented plasma-induced damage to chemical bath deposited cadmium sulfide (CdS) buffer, thereby enabling the maintenance of high-quality junctions using a thin CdS buffer layer (≈30nm). Interfacial engineering with LGO improved the Voc of the CZTSSe TFSCs from 466 to 502mV. Furthermore, the tunable work function obtained through Li doping generated a more favorable band offset in CdS/LGO/MGZO interfaces, thereby, improving the electron collection. The MGZO/LGO TE/ETL combination achieved a power conversion efficiency of 10.67%, which is considerably higher than that of conventional AZO/intrinsic ZnO (8.33%).

Modeling of a New Solar Cell Model with ZnO/CdS Core-Shell Nanowire Arrays Embedded in a CZTS Absorber

Copper-zinc-tin-sulfide (CZTS) solar cells are increasingly attracting researchers due to their low cost, non-radioactive behavior, and environmental friendliness. A SCAPS simulation study of these solar cells with zinc oxide (ZnO)/cadmium sulfide (CdS) core-shell nanowires and different thicknesses of absorber, buffer, and window is described in this study. The study resulted in an optimized model with a CZTS absorber, a CdS buffer, and a ZnO window with respective thicknesses of 830 nm, 90 nm, and 140 nm, efficiency (EFF) of 16.62%, a factor of fill (FF) of 81.75%, open circuit voltage (Voc) of 0.61 V and short circuit current density (Jsc) of 6.3 cmA/cm 2 . These results are very close to those reported in the literature. Keywords: CZTS; Efficiency; shell thickness; ZnO/CdS core-shell nanowires; SCAPS. DOI: 10.7176/JETP/13-1-01 Publication date: January 31 st 2023

Simulation analysis of Cd-free Cu(In,Ga)Se2 solar cells with novel BiOX (X=Cl, Br) buffer layers

Nowadays, cadmium sulfide (CdS) or zinc oxysulfide (Zn(O,S)) are the traditional buffer layer of Cu(In,Ga)Se2 (CIGS) solar cells. However, these buffer layers contain several disadvantages, such as the complicated synthesis problem and heavy metal toxicity. To solve the above problems, the potential of Bi-based (BiOX: X = Cl, Br) materials employed as buffer layers for efficient CIGS solar cells are investigated by using SCAPS simulation software in this contribution. It can be found that all BiOX materials fabricated from a soft liquid deposition process possess 2D nanosheet structures. A comparison of 2D nanosheet size reveals that BiOBr can form easily compared with BiOCl under the same growth conditions. Simultaneously, DRS and XPS determine the energy band distribution of BiOX materials. Further investigations on the simulated device performance suggest that conversion efficiency of the BiOBr sample is maximum, which is close to that of CdS and much larger than the BiOCl sample, mostly owning to the increased JSC and FF. The reason for this results is that the energy band distribution of BiOBr is similar to that of CdS buffer layer. It also indicates that BiOBr has the potential to serve as a buffer layer material for solar cells.

SnS2 Nanoparticles and Thin Film for Application as an Adsorbent and Photovoltaic Buffer.

Energy consumption and environmental pollution are major issues faced by the world. The present study introduces a single solution using SnS2 for these two major global problems. SnS2 nanoparticles and thin films were explored as an adsorbent to remove organic toxic materials (Rhodamine B (RhB)) from water and an alternative to the toxic cadmium sulfide (CdS) buffer for thin-film solar cells, respectively. Primary characterization tools such as X-ray photoelectron spectroscopy (XPS), Raman, X-ray diffraction (XRD), and UV-Vis-NIR spectroscopy were used to analyze the SnS2 nanoparticles and thin films. At a reaction time of 180 min, 0.4 g/L of SnS2 nanoparticles showed the highest adsorption capacity of 85% for RhB (10 ppm), indicating that SnS2 is an appropriate adsorbent. The fabricated Cu(In,Ga)Se2 (CIGS) device with SnS2 as a buffer showed a conversion efficiency (~5.1%) close to that (~7.5%) of a device fabricated with the conventional CdS buffer, suggesting that SnS2 has potential as an alternative buffer.

Effect of absorber layer bandgap of CIGS-based solar cell with (CdS/ZnS) buffer layer

This article uses computational models to evaluate the potential of copper-indium-gallium-diselenide (CIGS) thin film solar cells. The use of cadmium sulphide (CdS) renders the solar cell environmentally hazardous. A zinc sulphide (ZnS) that is non-toxic and has a large bandgap is studied as a potential replacement for cadmium sulphide in CIGS-based solar cells. The present research focuses on the impact of the CIGS-based solar cell bandgap absorber layer by increasing the absorber layer thickness (0.1-2 μm) using the solar cell simulator simulation tool SCAPS. The basic simulation produces 18.2 % efficiency with a CdS buffer layer, which is 9.95% better than the previously published work. The Simulated efficiency is 22.16% for the CIGS solar cell using ZnS. The simulation of solar cell characteristics of how the thickness of the absorber layer, the gallium grading (efficiency ranges up to 22.25 %) is demonstrated, showing the effect of buffer layer (ZnS) on the current of short-circuit density (JSC), open-circuit voltage (Voc), fill factor (FF), and efficiency (η) of the solar cell.

Characteristics of TAA-ZnS Buffer Layer by Addition of Sodium Citrate for CIGS Thin Film Solar Cell.

Zinc Sulfide (ZnS) is an environmentally friendly material with a wide bandgap (Eg = 3.7 eV) comparable to that of cadmium sulfide (CdS) (2.4 eV), which is conventionally used as buffer layer in Cu(In,Ga)Se2 (CIGS) thin film solar cells. Conventional ZnS buffer layers are manufactured using thiourea, and, these layers possess a disadvantage in that their deposition rate is lower than that of CdS buffer layers. In this paper, thioacetamide (TAA) was used as a sulfur precursor instead of thiourea to increase the deposition rate. However, the ZnS thin films deposited with TAA exhibited a higher roughness than the ZnS thin films deposited with thiourea. Sodium citrate was therefore added to increase the uniformity and decrease the roughness of the former ZnS thin films. When sodium citrate was used, the thin films demonstrated a high transmittance via the controlled generation of particles. In the case of TAA-ZnS thin films doped with a sodium citrate concentration of 0.04 M, the granules on the surface disappeared and these thin films were denser than the TAA-ZnS thin films deposited with a lower sodium citrate concentration. It is considered that the rate of the ion-by-ion reaction increased due to the addition of sodium citrate, thereby resulting in a uniform thin film. Consequently, TAA-ZnS thin films with thicknesses of approximately 40 nm and high transmittances of 83% were obtained when a sodium citrate concentration of 0.04 M was used.

Defect Analysis of Solution-Based Process CIGS Thin-Film Solar Cells Using Technology Computer-Aided Design.

Copper indium gallium sulfur selenide (Cu(In1-xGax)SeS, CIGS) thin film solar cells are fabricated using a solution-based process, and their defect models are studied through a computer-aided design method. Cu(In1-xGax)SeS is structured with a graded bandgap by controlling the ambient gas and precursor composition, during the fabrication process. The defects in the CIGS are modeled as two donor-like defects, which are differently distributed as per the CIGS grain size (large and small grains at upper and bottom layers, respectively), whereas those in the cadmium sulfide (CdS)/CIGS interface are modeled as a complex model of both donor- and acceptor-like defects in the CdS, near the interface. By measuring the external quantum efficiency and current density-voltage characteristics, the best-fitting match of the simulated values with the measured values are obtained. The simulation results demonstrate that the defects (defect density of ~7 × 1018) in the CdS interface are more serious, compared to the CIGS defects (defect density of ~2 × 1015 in the bottom), which were initially expected to be more severe because of grain nonuniformity. For increasing the cell efficiency, we establish that the process and material quality need to be further improved not only during CIGS formation using a multistep spin-coated precursor but also during the initial deposition of the CdS buffer. This numerical approach can enable better understanding of the defect behavior in solar cells, and indicate directions for improvement in the fabrication process and device structure, for developing high-efficiency solution-based CIGS solar cells.

Improvement of the CIGS solar cell performance: structure based on a ZnS buffer layer

Cu(In,Ga)Se2 (CIGS) based thin film solar cells are the most efficient thin-film solar cells today. The non-toxic and wide band-gap zinc sulphide (ZnS) is a promising material to replace the cadmium sulfide (CdS) as the buffer layer in CIGS based solar cells. In this work we present a simulation study of a CIGS based solar cell with a buffer layer of ZnS, using the simulator Silvaco-Atlas. Our primary simulation shows a 22.6% efficiency of the CIGS solar cell with the CdS buffer layer which is comparable to reported and highest experimental results. However, the simulated efficiency of the CIGS solar cell with the ZnS buffer layer as high as 23.54% was achieved. The effects of layer parameters like the thickness, the acceptor and donor densities of the CIGS absorber and ZnS buffer layers and the CBO on the photovoltaic parameters of the ZnS/CIGS solar cell are optimized in order to improve the performance of the ZnS/CIGS solar cell. The highest efficiency of 27.33% is achieved when the ZnS buffer and the CIGS absorber layers have thicknesses of 0.025 µm and 4 µm with acceptor and donor densities of 6 × 1017 cm−3 and 1018 cm−3, respectively and a CBO in the range − 0.05 to 0.05 eV. The present results of simulation can help the development of the solar cells with higher conversion efficiency and low cost.

Optimization of CdxZn1-xS compound from CdS/ZnS bi-layers deposited by chemical bath deposition for thin film solar cells application

In this paper, we report results on the processing of cadmium zinc sulfide (CdxZn1-xS) ternary compound starting from the deposition of cadmium sulfide (CdS)/zinc sulfide (ZnS) bi-layers buffer configuration and a subsequent thermal annealing for its application to thin film solar cells. The impact of different CdS/ZnS bi-layers buffer configurations as effective alternative to the single CdS buffer layer, as well as the physical and chemical properties of the equivalent CdxZn1-xS ternary compound are presented and discussed. Results on physical properties optimization of CdxZn1-xS ternary compound for future applications to thin film solar cells are presented.

High-Efficiency Cu(In,Ga)Se₂ Thin Film Solar Cells Using ZnS and CdS Buffer Layers.

Most of the existing copper indium gallium diselenide (CIGS) thin film solar cells are based on a cadmium sulfide (CdS) buffer layer fabricated using a chemical bath deposition (CBD) process. However, due to environmental pollution caused by material toxicity and the unique wet process's incompatibility with the vacuum process, many studies are now being actively carried out on nontoxic buffer layers. In this study, to replace CdS buffer layers, zinc sulfide (ZnS) buffer layers with a big band gap and a low optical loss at a short wavelength were fabricated using a magnetron sputtering system. For comparative analysis, this study also fabricated CdS buffer layers using the CBD process. Then, the conversion efficiency of CIGS thin film solar cells deposited with ZnS and CdS thin film as buffer layers was measured. The light conversion efficiency of ZnS buffer layer-based CIGS was measured at 14.44%, while that of the CdS buffer layer-based CIGS was measured at 15.71%. Given that both are higher than the minimum conversion efficiency required for commercialization (10%), ZnS buffer layer-based solar cells could have a competitive edge over the existing CdS buffer layer-based solar cells.

Study of photovoltaic performance of Sb2S3/CdS quantum dot co-sensitized solar cells fabricated using iodine-based gel polymer electrolytes

In this study, cadmium sulfide (CdS) and antimony sulfide (Sb2S3) quantum dot (QD) co-sensitized solar cells were fabricated using iodine-based gel polymer electrolytes. It was noticed that in comparison with TiO2/Sb2S3 QDs, the short-circuit current (Jsc) and the photoconversion efficiency (η) of the fabricated photovoltaic device based on TiO2/CdS/Sb2S3 QDs increased from 5.61 to 8.35 mA/cm2 and 1.06–1.61%, respectively. The presence of a CdS buffer layer between TiO2 and Sb2S3 was attributed to the enhancement of Jsc and η. The CdS buffer layer promoted the growth of Sb2S3 and facilitated the transfer of electrons from Sb2S3 to TiO2 through the reorganization of band levels between CdS and Sb2S3. It was also observed that the polymer electrolytes effectively prevented the corrosion of Sb2S3 QDs. Therefore, it can be concluded that the outcomes of this research could expedite future work on novel Sb2S3 quantum dot sensitized solar cells (QDSCs) based on polymer electrolytes with improved performance.

Realizing zinc-doping of CdS buffer layer via partial electrolyte treatment to improve the efficiency of Cu2ZnSnS4 solar cells

Cadmium sulfide (CdS) is the most widely used buffer material for a variety of thin-film solar cells including Cu2ZnSnS4. However, reports have shown that CdS film obtained by chemical bath deposition (CBD) is not the ideal buffer layer for pure sulfide CZTS solar cell. Zinc doping is a viable approach to modifying the CdS buffer film, but the present methods are far from satisfactory. Here, we innovatively developed an effective way of Zinc doping using partial electrolyte (PE) treatment, resulting in state-of-the-art buffer layer for solar cells based on high-surface-waviness CZTS light absorber. Our study shows that this Zn PE-treated CdS film improved the properties including coverage, full-range light transmittance and conduction band alignment with CZTS. Ultimately, the resultant modified CdS film boosted the open-circuit voltage of our devices by more than 100 mV, yielding power conversion efficiency (PCE) of 3.30%. We note that this is the highest efficiency that has been reported for all solution-processed CZTS solar cells.

Prospects of potential ZnMgO front layer in CZTS solar cells

In the CZTS structure, ZnMgO alloy can be a promising alternative buffer layer candidate to toxic cadmium sulphide (CdS) material. The effects of conduction band offset (CBO) at ZnMgO/CZTS interface are investigated by numerical approach. The main factor examined is the Mg concentration of ZnMgO and at high values of this parameter, a significantly higher barrier is observed, leading to a distortion in the current-voltage curve (S-shape). This phenomenon caused by degraded open circuit voltage (Voc) and fill factor (FF) parameters leads to overall poor performance. Zn1-xMgxO with 20% Mg concentration decreases maximally the CBO and eliminates the S-shape while increasing the conversion efficiency. The suggested design by ultimately replacing both CdS buffer and ZnO window layers by a single layer of ZnMgO leads to an optimised CZTS based solar cell exhibiting a conversion efficiency of 11.50% with Voc = 0.78 V, Jsc = 22.37 mA/cm² and FF = 66.11%.

Improved Efficiency of Microcrystalline Silicon Thin-Film Solar Cells With Wide Bandgap CdS Buffer Layer

In this paper, we have reported a new structure based upon an optical simulation of maximum light trapping and management in microcrystalline silicon thin-film solar cells by using multitexture schemes and introducing an n-type cadmium sulphide (CdS) buffer layer with the goal of extreme light coupling and absorption in silicon absorber layer. Photon absorption was improved by optimizing the front and back texturing of transparent conductive oxide layers and variation in buffer layer thickness. We have demonstrated that light trapping can be improved with the proposed geometry of 1- μm-thick crystalline silicon absorber layer below a thin layer of wide bandgap material. We have improved the short-circuit current densities by 1.35 mA/cm2 resulting in a total short-circuit current of 25 mA/cm2 and conversion efficiency of 9 % with the addition of CdS buffer layer and multitextures, under global AM1.5 conditions. In this study, we have used a two-dimensional full-vectorial finite element to design and optimize the proposed light propagation in solar cell structure configuration. Our simulation results show that interface morphology of CdS layer thickness and textures with different aspect and ratios have the most prominent influence on solar cell performance in terms of both short-circuit current and quantum efficiency.

Non-Toxic Buffer Layers in Flexible Cu(In,Ga)Se2Photovoltaic Cell Applications with Optimized Absorber Thickness

Absorber layer thickness gradient in Cu(In1−xGax)Se2(CIGS) based solar cells and several substitutes for typical cadmium sulfide (CdS) buffer layers, such as ZnS, ZnO, ZnS(O,OH), Zn1−xSnxOy(ZTO), ZnSe, and In2S3, have been analyzed by a device emulation program and tool (ADEPT 2.1) to determine optimum efficiency. As a reference type, the CIGS cell with CdS buffer provides a theoretical efficiency of 23.23% when the optimum absorber layer thickness was determined as 1.6 μm. It is also observed that this highly efficient CIGS cell would have an absorber layer thickness between 1 μm and 2 μm whereas the optimum buffer layer thickness would be within the range of 0.04–0.06 μm. Among all the cells with various buffer layers, the best energy conversion efficiency of 24.62% has been achieved for the ZnO buffer layer based cell. The simulation results with ZnS and ZnO based buffer layer materials instead of using CdS indicate that the cell performance would be better than that of the CdS buffer layer based cell. Although the cells with ZnS(O,OH), ZTO, ZnSe, and In2S3buffer layers provide slightly lower efficiencies than that of the CdS buffer based cell, the use of these materials would not be deleterious for the environment because of their non-carcinogenic and non-toxic nature.

Investigations on the mechanical properties of the elementary thin films composing a CuIn1 − xGaxSe2 solar cell using the nanoindentation technique

In this investigation, the mechanical properties of the different layers composing a CuIn1−xGaxSe2 (CIGS) based solar cell were studied. Magnetron sputtering technique was used for the deposition of these layers except for the cadmium sulphide (CdS) layer which was deposited using chemical bath deposition process. We performed several indentation tests on the individual layers, i.e. molybdenum (Mo) back contact layer, CIGS absorber layer, CdS and alternative zinc sulphide oxide (ZnOS) buffer layers, and zinc oxide (ZnO)-AZO (aluminium-doped zinc oxide) transparent window layer; all were deposited on glass substrates. We report the values of the hardness (H) and of the Young's modulus (E) for each material, using indentation tests and an analytical model. The Mo layer remained the hardest and the most rigid, with H=8.7GPa and E=185GPa, while the CIGS layer has shown poor mechanical properties with H=3GPa and E=58GPa. On the other hand, the observed similarity in mechanical properties of the ZnO and ZnOS layers might be attributed to the similarity of their microstructures.

Pulsed-DC magnetron sputtering of intrinsic ZnO film and its application to CIS solar cell

To create an intermediate layer in CuInSe2(CIS)-based solar cells, an intrinsic zinc oxide(i-ZnO) thin film was deposited on a glass substrate and a cadmium sulfide(CdS) buffer layer using an in-line pulsed-DC sputtering. In comparison with i-ZnO films sputtered using RF power, i-ZnO films sputtered using pulsed-DC power showed much higher deposition rates and similar structural characteristics, without causing any damage to the CdS buffer layer. During pulsed-DC sputtering, the O2/Ar gas ratio, reverse time, and pulse frequency were changed to optimize the process parameters. From the transmittance and scanning electron microscope(SEM) images, the optimized i-ZnO film was obtained at an O2/Ar gas ratio of 1%, a pulsed frequency of 200 kHz, and a reverse time of 1.3 μs. For showing the feasibility, it was applied to the fabrication of a CIS solar cell which was processed using the two step method by the rapid thermal processing (RTP) annealing of Cu–In stacked layers. It showed a possibility of the pulsed-DC sputtered ZnO as an intermediate layer of a CIS solar cell even though a cell efficiency was shown with a low value of 2.2% due to an early stage of our study in the two step CIS process.

Deposition and characterization of cadmium sulfide (CdS) by chemical bath deposition using an alternative chemistry cadmium precursor

A uniform ultrathin (<30nm) CdS buffer layer was deposited by CBD by utilizing an alternative bath based on N-methylthiourea and was compared with the standard sulfur source. The CdS deposited by this new bath formulation was deposited separately on soda lime glass (SLG), sputtered molybdenum/glass and co-evaporated copper indium gallium di-selenide (CIGS)/Mo/glass substrates. The CdS film properties were investigated by scanning electric microscope (SEM), X-ray diffraction (XRD), X-ray photoelectric spectroscopy (XPS), UV–vis spectroscopy, and quantum efficiency (QE). The films deposited with N-methylthiourea were found to have a similar granular structure, deposit in the same stoichiometry, and have similar device performance as the standard when deposited in the 60–80nm film thickness range. When the CdS layer was deposited ultrathin in the 20–30nm range, it was found to have good surface coverage with no evidence pinholes or device shunting. QE data indicated 40nm thick CdS samples deposited using Thiourea as a sulfur source demonstrated better overall results however depositing a 20nm thick CdS demonstrated N-methylthiourea as a sulfur source could deposit with good quantum efficiency and more consistently. Devices fabricated with ultrathin CdS using N-metyhlthiourea showed better device performance compared with devices fabricated using the standard CdS chemistry.

Impact of maximum copper content during the 3-stage process on CdS thickness tolerance in Cu(In,Ga)Se2-based solar cell

ABSTRACTThe tolerance of photovoltaic performances of Cu(In,Ga)Se2-based (CIGSe) solar cells prepared from 3-stage grown absorbers to cadmium sulfide (CdS) buffer layer thickness was investigated. We focus on the influence of the maximum Cu content y = [Cu]/([In]+[Ga]) reached during the co-evaporation process on this tolerance. By increasing the duration of the 2nd stage we varied ymax from 0.93±0.11 up to 1.06±0.12. Although final Cu content and CIGSe surface morphology seem to be similar for all absorbers, the photovoltaic performance of cells with higher maximum Cu content are better; moreover they tolerate much thinner CdS buffers (down to 10 nm-thick) without open circuit voltage or fill factor loss. Cells with lower ymax exhibit more erratic performance and J(V,T) measurements show a specific voltage distribution for thin CdS. From these results it appears possible to decrease the CdS buffer layer thickness if it is deposited on adapted absorbers.