Performance Of CZTS Solar Cells Research Articles

Novel buffer layer on the performance of CZTS solar cells by numerical simulation

Cu2ZnSnS4 as the promising absorber layer material, has received great attention in the application of highly efficient and low-cost thin film solar cells. The theoretical photovoltaic conversion efficiency of the CZTS thin-film solar cells reaches up to around 32%. Conventionally, CdS or CdSe have been used as buffer layers in these cells. However, cadmium's toxicity and volatility pose environmental concerns. This paper explores TiNxOy and CrNxOy as buffer layers in CZTS solar cells, investigated through numerical simulations using SCAPS-1D. Thickness and carrier concentration on the solar cell performance are mainly investigated. Effects of conduction band offset and defect density on photovoltaic parameters of CZTS/TiNxOy and CZTS/CrNxOy solar cells are also simulated based on the optimal thickness and carrier concentration. The simulation results point out that the photovoltaic conversion efficiency of both systems achieves 22% when TiNxOy or CrNxOy is used as buffer layers. Notably, compared with the CZTS/CrNxOy solar cell structure, TiNxOy as the buffer layer provides a more compatible band offset with the CZTS layer.

Experimental study and numerical simulation for the development of critical performance parameters of eco-friendly Cu2ZnSnS4-based solar cells

This work aims to study the basic Characteristics of CZTS thin films produced by chemical solution process in addition to a numerical study of the CZTS-based solar cells. In this context, eco-friendly and cost effective thin films of CZTS were coated on glass substrates by sol–gel dip-coating method. This method is used to grow crystalline CZTS thin films without sulfidation processes. The structural and optical properties have been carried out by X-ray Diffraction (XRD) and UV/Visible spectroscopy. The oxidation states of CZTS thin film have been studied by, X-ray photoelectron spectroscopy XPS analysis. The performance of CZTS solar cells has been investigated with the simulator SCAPS-1 D. The impact of different parameters like the CZTS absorber layer thickness, the carrier doping density and the operation temperature has been studied to get better understanding of the properties of our cells.

Enhancing Hole Density and Suppressing Recombination Centers through Illumination in Kesterite Thin Film Solar Cells.

Enhancing carrier density and increasing carrier lifetime are critical for the good performance of thin film solar cells. We apply illumination during the growth of kesterite Cu2ZnSnS4 (CZTS) to enhance hole density and suppress defects of nonradiative electron-hole recombination centers simultaneously. To examine the effect of the injected carriers generated by illumination, we first extend the scheme of detailed balance equations relating free carriers and defects beyond thermal equilibrium conditions by developing an extended Fermi level (EF') to characterize a homogeneous semiconductor with non-equilibrium carriers. On the basis of this scheme, we find that illumination can promote the formation of carrier-providing defects and suppress the formation of carrier-compensating defects. Then, we demonstrate that applying proper illumination during the growth of CZTS will help achieve a higher hole density and simultaneously suppress the formation of the SnZn antisite significantly, which are beneficial for the performance of CZTS solar cells.

Impact of the secondary phase ZnS on CZTS performance solar cells using simulation program

In the present work ,Scaps 1d software is used to study the effect of ZnS secondary phase on the performance of solar cells. The standard CZTS-based devices are composed of a multilayer thin film formed on soda-lime glass (SLG), Mo/MoS2/CZTS/Cds/i-ZnO/ZnO Al. a metallic molybdenum (Mo) back electrode, MoS2 built between the absorber and the back contact; a p-CZTS absorber layer; an n-type buffer layer, typically Cds to form the junction of the solar cell, a TCO doped ZnO layer and a transparent ZnO:Al front contact. Ni/Al metal contact grids complete the cell. An ultrathin layer of ZnS is placed in the standard solar cell structure between the Cds buffer layer and the CZTS absorber layer to represent the second phase (SP) above CZTS [1].Cell characteristics such as ƞ, FF, Jsc , and Voc were studied. The formation of ZnS on the surface of CZTS has negative effects on the solar cell parameters where the conversion efficiency ƞ decreases.The impact of this layer on the performance of CZTS solar cells is also investigated through the results obtained from the analysis of the complex impedance (Z*) and the modulus (M*). An equivalent circuit of the solar cell consisting of series and parallel resistors has been evolved to study the electrical behavior around each interface of this structure.This new procedure has been very beneficial for the identity of the most important parameters of the diffusion and recombination process.

Heterojunction post-heat treatment process driving high efficiency for Cu2ZnSnS4 solar cell

The quality of Cu2ZnSnS4 (CZTS) absorber layer, Mo/CZTS interface and heterojunction CZTS/CdS are the most important factors directly affecting the performance of CZTS solar cells. On the base of high quality absorber layer and back contact interface, the effects of post-heat treatment (PHT) process of CZTS/CdS on the quality of heterojunction and device performance have been comprehensively investigated. The PHT process can promote the elements in the heterojunction region interdiffuse between absorber and buffer layer, i.e., more Cd elements diffuse to CZTS, and Zn, Cu elements diffuse to CdS. Consequently, the elements interdiffusion affects the chemical composition of the absorber layer surface and the band alignment of the heterojunction. After applying the PHT process, the surface of CZTS becomes Cu-poorer in comparison to the CZTS bulk. Due to the diffusion of Cd2+into the CZTS layer, the free carrier density is increased. In addition, PHT process can also promote the recrystallization of CdS and thus greatly improve the crystallization quality of CdS. Owing to the more favorable band alignment at the CZTS/CdS interface as well as better crystallinity of CdS, higher quality heterojunction was obtained. Finally, at the optimized PHT temperature of 275 °C, a pure CZTS solar cell with active area efficiency of 9.75% (total area efficiency: 8.90%) has been fabricated. Based on the application of PHT process, reducing the deep level defects in CZTS bulk is expected to further improve the device performance.

Comparative device performance of CZTS solar cell with alternative back contact

In this study we report the comparative study of CZTS/CdS solar cell device with two different back contacts. The device configuration of ITO/CZTS/CdS and Ni/CZTS/CdS are fabricated and characterized. By varying the back-contact work function of device the performance of the solar cell device is enhanced. A high work function back contact could effectively make a near-ohmic contact with high bandgap p-type semiconductor. We here experimentally showed the improvement in device efficiency by employing high work function back contact for CZTS device. The comparative devices exhibited performance, with open-circuit voltage of 0.16 V and 0.36 V and conversion efficiency of 0.74% and 2.33% for ITO/CZTS/CdS and Ni/CZTS/CdS device respectively. We numerically replicated this enhancement using work-function as parameters in simulations.

Effect of Mg doping on Cu2ZnSnS4 solar cells prepared by DMF-based solution method

In this paper, magnesium was successfully introduced into CZTS using the DMF-based solution method, and CZMTS solar cell was prepared. The effects of Mg doping on the morphology, crystal structure, and electronic properties of the CZTS absorber were investigated in detail. The crystal structure of the CZMTS absorber and the chemical valence states of the other elements (Cu, Zn, Sn, and S) were not changed as shown by XRD, Raman, and XPS analyses. The results show that Mg doping can improve the electronic properties and microstructure of CZTS absorbers, thus enhancing the PCE from 2.91% to 4.10%. This performance enhancement is associated with good crystal quality, reduced cation-disordering defects, and high external quantum efficiency at the longwave region caused less recombination and open circuit voltage loss. Therefore, Mg doping has a positive effect on improving the performance of CZTS solar cells. • The feasibility of the DMF-based solution method to achieve Mg doping is demonstrated. • Mg doping can reduce recombination and open-circuit voltage loss of CZTS solar cells. • After Mg doping, the PCE of CZTS solar cells is increased from 2.91% to 4.10%.

Contribution to sustainable and environmental friendly non-toxic CZTS solar cell with an innovative hybrid buffer layer

Due to non-toxicity and earth abundancy of raw materials, CZTS grabbing the attention of researchers to make it highly efficient and cost-effective solar cell harvesting. Thin-film CZTS based solar cell of higher efficiency reported with conventional CdS layer. Toxicity of Cd influences to reduce the thickness of the CdS buffer layer without compromising with the efficiency. The present paper deals with CdS/In2S3 and CdS/ZnS hybrid buffer layer which is more efficient than the solar cell using only the CdS buffer layer. The reduced thickness of the CdS layer in CZTS/CdS/In2S3/ZnO: Al and CZTS/CdS/ZnS/ZnO: Al structures have been optimized by using SCAPS-1D simulation software. This study reveals that there is an enhancement in the performance of solar cells from η = 15.68% with CdS to η = 16.52% with CdS/In2S3 and η = 15.81% with CdS/ZnS hybrid buffer layer. Variation in PV parameters with a variation of the thickness of the buffer and absorber layer has been optimized. The acceptor density of CZTS/CdS/In2S3 and CZTS/CdS/ZnS was varied and results have been optimized. A numerical study of both structures on the photovoltaic performance of CZTS solar cells has been done by using SCAPS-1D simulation software.

Improving the performance of Cu2ZnSnS4 thin film solar cell by engineering the ITO film thickness

In this work, the effects of tin doped indium oxide (ITO) thin films with different thicknesses (50 nm–476 nm) on the optoelectronic performance were investigated. Meanwhile, the sputtered ITO layers were annealed at 180 °C for 60min under air atmosphere. The result indicated that the electro-optical properties of ITO films with the thickness (383 nm) were optimum, and the corresponding resistivity and average reflectance in the spectrum range (350–860 nm) were 4.73 × 10−4 Ω cm and lower than 20%, respectively. Finally, impacts of ITO layers with various thicknesses on the performance of CZTS solar cells were also studied. The open circuit voltage (Voc), short circuit current density (Jsc), fill factor (FF) and power conversion efficiency (PCE) of CZTS solar cells had been increased significantly from 576 mV to 636 mV, from 15.8 mA/cm2 to 20.2 mA/cm2, from 31.2% to 43.4% and from 3.04% to 5.56%, respectively, and eventually the highest PCE of CZTS solar cell based on 383 nm ITO window layer thickness was 5.56%.

Simulation study to find suitable dopants of CdS buffer layer for CZTS solar cell

The performance of CZTS solar cell, a promising candidate in the field of energy production from sunlight, can be improved by optimizing the parameters of most widely used CdS buffer layer. In this work, numerical study have been done on the typical CZTS solar cell structures containing Mo thin film as back contact on glass substrate using SCAPS-1D solar cell simulation software. Then, the CZTS has been used as the absorber layer followed by CdS buffer later. Following, ZnO and transparent conducting oxide n-ITO layers have been considered as window layer and front contact, respectively. In the simulations, the CdS buffer layer has been doped with three different materials such as Silver (Ag), Copper (Cu) and Chlorine (Cl) for a wide acceptable range of carrier concentration. After obtaining the suitable carrier concentration, the thickness of the doped buffer layer has been varied keeping other layer parameters constant to see the variation of performance parameters open circuit voltage (Voc), short circuit current density (Jsc), fill factor (FF) and efficiency (η) of the CZTS solar cell.

Influence of composition ratio on the performances of kesterite solar cell with double CZTS layers—A numerical approach

Effects of double CZTS layers with different composition ratio Cu/Zn in which a high copper concentration at the bottom and a low copper concentration at the top on the physical parameters and cell performance of CZTS solar cells by using the one-dimensional SCAPS-1D numerical model have been analyzed and discussed. In this study, it is demonstrated that a numerical analysis can provide informative predictions of the CZTS solar cell's performance proposed. The agreement between simulated and observed data was sufficient to indicate that the general response of the cell performance is reasonably represented. The high Cu/Zn ratio of the bottom layer was shown as very influential on the parameters of solar cells, where: (i) this bottom layer becomes an electrical mirror for the minority carriers, (ii) effective surface recombination velocity reduce, (iii) Auger recombination mechanism become more important, (iv) high efficiency depends strongly on the larger thickness of top layer, and finally (v) bandgap energy of bottom layer decreases and achieved best cell performance.

UV-ozone induced surface passivation to enhance the performance of Cu2ZnSnS4 solar cells

Interface property has been considered one of the most critical factors affecting the performance of semiconductor devices. In this work, we demonstrate an efficient surface passivation for the interface between Cu2ZnSnS4 (CZTS) and CdS buffer layer by using UV-ozone treatment at room temperature. The passivation led to a significant enhancement of short circuit current density (Jsc) of the device from 11.70 mA/cm2 to 18.34 mA/cm2 and thus efficiency of the CZTS solar cells from 3.18% to 5.55%. The study of surface chemistry has revealed that the UV-ozone exposure led to formation of a Sn–O rich surface on CZTS, which passivates the dangling bonds and forms an ultra-thin energy barrier layer at the interface of CZTS/CdS. The barrier is considered to be responsible for the reduction of non-radiative recombination loss in the solar cells as confirmed by photoluminescence (PL) measurement. The elongated lifetime of minority carriers in the CZTS solar cells by time-resolved PL has further verified the interface passivation effect induced by UV-ozone treatment. This work provides a fast, simple yet very effective approach for surface passivation of CZTS film to boost the performance of CZTS solar cells.

Influence of stacking order and intermediate phase at low temperature on Cu2ZnSnS4 thin film formation for solar cell

A stacking order of a precursor is one of the important factors that affects the quality of Cu2ZnSnS4 (CZTS) thin film. Understanding of the intermediate phase formation and its reaction mechanism can contribute to the design of a precursor to enhance the performance of CZTS solar cell. In this work, three precursors such as Zn/SnS/Cu, SnS/Cu/Zn, and SnS/Zn/Cu were designed based on previous studies. These precursors were treated for sulfurization process at 560 °C, and annealed at 300 °C for 30 min to investigate the reaction of intermediate phases. The annealed thin film from Zn/SnS/Cu precursor exhibited crystallized and uniform intermediate ternary phase of Cu2SnS3. This easy and uniform transformation to Cu2SnS3 phase as a whole at low temperature using Zn/SnS/Cu precursor resulted in relatively smooth surface of CZTS thin film after sulfurization at high temperature. In contrast, CZTS thin film from SnS/Cu/Zn or SnS/Zn/Cu precursor showed a rough surface morphology with loss of Zn content. A rough surface will degrade the contact between CZTS absorber and CdS buffer layers, resulting in decreased a device performance. Accordingly, CZTS solar cell device fabricated from Zn/SnS/Cu precursor achieved improved efficiency of 4.20%.

Improving the charge separation and collection at the buffer/absorber interface by double-layered Mn-substituted CZTS

A non-ideal buffer-absorber interface due to interface recombination is one of the limitations in Cu2ZnSnS4 (CZTS) solar cells. An absorber gradient using partial cation-substitution is one possible solution to this issue by reducing interface recombination sites and improving band alignment. Partial substitution of Zn with Mn is a potentially attractive concept owing to its abundance as well as similar size and electronic properties compared to Zn. In this study, Cu2MnxZn1-xSnS4 (CMZTS) thin film were fabricated by a sol-gel spin coating technique to understand the effect of Mn on the device performance. X-ray diffraction (XRD) and Raman analysis confirm Mn substitution for Zn in the crystal lattice of Cu2ZnSnS4 (CZTS) with no secondary phases detected for x ≤ 0.4. Enhancement of short circuit current (Jsc) in Cu2Mn0.15Zn0.85SnS4 has led to improved efficiency in comparison with CZTS. Since external quantum efficiency (EQE) indicates the short wavelength collection as the main reason for the improved Jsc, we designed a double layered structure of CZTS as bottom layer and CM0.15Z0.85TS as top layer. With this structure, we obtained our best performance cell with power conversion efficiency (PCE) of 5.73% and Jsc of 17.86 mA/cm2. The improved Jsc is attributed to increased depletion width and higher activation energy of the limiting recombination mechanism as shown by capacitance-voltage and temperature dependent current-voltage measurements. Our study concludes that CM0.15Z0.85TS top layer improves the interface quality of the p-n junction and may be an alternative method to improve the performance of CZTS solar cells.

Dual function of ultrathin Ti intermediate layers in CZTS solar cells: Sulfur blocking and charge enhancement

An ultrathin Ti film acting as both an intermediate layer and a dopant was inserted at the interface between Mo and Cu2ZnSnS4 (CZTS) to improve the performance of CZTS solar cells. Different from previously reported blocking layers, the Ti intermediate layer inhibited the formation of a MoS2 layer and voids at the interface between the Mo and CZTS absorber and also influenced the crystallinity, surface evenness, Hall mobility, and absorptivity of the CZTS absorber. When the thickness of the Ti blocking layer increased to 20nm, the conversion efficiency of the solar cell increased by 57%, along with an increase in the open-circuit voltage of 32%. The effect of the Ti layer on the microstructure and performance of the CZTS film is discussed here in detail. These results serve as guiding principles for preparing high-quality CZTS thin films for potential applications in low-cost solar cells.

Prospects of Zn(O,S) as an alternative buffer layer for Cu 2 ZnSnS 4 thin‐film solar cells from numerical simulation

Zn(O,S) is an attractive alternative to CdS as a buffer layer of Cu2ZnSnS4 (CZTS)-based solar cell due to its higher bandgap and environmental friendliness. In this work, CZTS solar cell with a structure of CZTS/Zn(O,S)/Al:ZnO was simulated by Solar Cell Capacitance Simulator (SCAPS). The impacts of thickness and acceptor concentration of CZTS, thickness and donor concentration of Zn(O,S) and operating temperature on the performance of CZTS solar cells were investigated. It has been obtained that the optimum thickness of CZTS is between 2000 and 3000 nm and that of Zn(O,S) is about 50 nm. The suitable doping concentrations of CZTS and Zn(O,S) layers are around 1016 and 1017 cm−3, respectively. The temperature coefficient of efficiency is about −0.023 %/K in the CZTS solar cell. All these simulation results will provide some important guidelines for fabricating high efficient CZTS solar cells.

Limitation factors for the performance of kesterite Cu2ZnSnS4thin film solar cells studied by defect characterization

PL, AS and DLCP have been performed to study the limitation factors for the performance of CZTS solar cells.