Efficiency Of CZTS Solar Cells Research Articles

A theoretical investigation to boost the efficiency of CZTS solar cells using SCAPS-1D

Cu2ZnSnS4 (CZTS) is predicted to be an efficient absorber than CIGS due to its cost effective, earth inabundant constituents. But, it reached a maximum experimental efficiency of 12.6% in 2013 and it remains the same for the past decade. This is due to the various crystallographic factors that limit the performance of CZTS like antisite defect formation, unfavourable band alignment with n-type CdS, etc. The major objective of this article is to identify potential strategies through which CZTS research can be pursued further using Solar Cell Capacitance Simulator (SCAPS) 1D simulator. First, it deals with understanding the difference between CZTS and its derivatives Cu2ZnSnSe4 (CZTSe) and Cu2ZnSn(SxSe1−x)4 (CZTSSe). Then, in pursuit of finding an alternative to n-CdS, the performance of various n-type semiconductors is investigated. Later, bandgap-graded structures using exponential and linear gradient laws are constructed and the performance of such structures is evaluated. Cation-substituted CZTS structures like (Ag1−xCux)2ZnSn(SxSe1−x)4(ACZTSSe) and Cu2Cd1−xZnxSn(SxSe1−x)4 (CCZTSSe) are discussed and the performance characteristics of such devices are also studied.

Regulation of solar cell performance by cadmium sulfide/copper-based thin film heterojunction annealing under different atmospheres

Efficient copper based thin film solar cells usually use inorganic n-type semiconductor material CdS as the buffer layer. Therefore, the interface quality and energy band matching between the buffer layer and the absorption layer are crucial to the collection and utilization of carriers. Heat treatment can promote the mutual diffusion of interface elements, the migration of ions in the material, and the change of defect state, and the appropriate temperature will change the Cu-Zn ordering degree in the absorption layer, so as to improve the efficiency of the solar cells. Based on the optimization of CdS basic process, the strategy of annealing CdS/copper-based thin film heterojunction in sulfur atmosphere further improves the quality of CdS thin film, and is applied to copper-based solar cells to regulate the p-n heterojunction energy band gap matching of copper-based thin film cells. The results show that the annealing of CdS thin film in sulfur-containing inert atmosphere can effectively improve the crystal quality of CdS thin film and inhibit the non-radiative recombination loss caused by defect trapping at the interface of CZTS/CdS heterojunction, and the open-circuit voltage of the device can significantly increase to 718 mV. In addition, annealing CZTS/CdS heterojunction in S/Ar atmosphere can effectively improve the p-n heterojunction energy band gap matching, which not only improves the electron transmission, but also reduces the carrier recombination, thus improving the <i>V</i><sub>oc</sub> and FF of the device. Besides, the oxygen element in CdS film can be replaced by sulfur element in sulfur atmosphere to improve the quality of CdS film, and thus enhancing the short-wave absorption of solar cell device. Therefore, in terms of device efficiency, the efficiency of CZTS solar cell based on sputtering method increases from 3.47% to 5.68%, which is about twice that of non-annealing treatment. Its device structure is Glass/Mo/CZTS/CdS/i-ZnO/Al:ZnO/Ni/Al, providing a reliable process window for copper based thin film solar cell devices to achieve high open-circuit voltage. Meanwhile, this study strongly demonstrates the importance of annealing atmosphere selection for CdS quality and energy band matching of CZTS/CdS heterojunction. In addition to interface interdiffusion, the composition and crystallinity of thin film material are controlled.

Numerical Simulation of an Improved CZTS/WS2 PV Cell by SCAPS 1-D

CZTS solar cells are promising among the third-generation solar cell. Because of its earth abundant materials and less toxicity CZTS solar cell can perform a sustainable role as an absorber layer. The optimization of a buffer layer is still a challenge and efficiency are still low than other thin film solar cells. In this study, WS2 buffer layer have been used to simulate the PV cell structure in SCAPS-1D simulation software. No research has been found where CZTS and WS2 is used together. We have achieved a maximum efficiency of η = 18.90 % at 300 K working temperature and other factors i.e., Voc, Jsc and FF are also promising. The highest certified efficiency of CZTS solar cell is nearly 12%. The simulation profile can be a guideline for fabricating the improved PV cell. GUB JOURNAL OF SCIENCE AND ENGINEERING, Vol 8, Dec 2021 P 41-48

The effect of Ag plasmonic nanoparticles on the efficiency of CZTS solar cell: an experimental investigation and numerical modelling

The effect of Ag plasmonic nanoparticles on the efficiency of CZTS solar cell: an experimental investigation and numerical modelling

Influence of “Productive” Impurities (Cd, Na, O) on the Properties of the Cu2ZnSnS4 Absorber of Model Solar Cells

Abstract The study focuses on the optical properties of the CZTS multicomponent semiconductor absorber with 3 % “production” impurities of Cd, Na, O within the framework of the density functional theory using the generalized gradient approximation and the SCAPS program, as well as investigates their influence on the performance and efficiency of CZTS-solar cells. The results showed that the introduction of Cd, Na, O impurities would lead to a decrease in the intensity of the absorption bands at 2.06 eV and 2.55 eV. The density of states CZTS: (Cd, Na, O) was determined from first principles, and it was revealed that impurities of Cd and O atoms would lead to a decrease in the band gap (to 0.9 eV and 0.79 eV), and an increase in Na impurity absorption (1.2 eV). It was also found that a decrease in the band gap led to a decrease in the open circuit voltage, and it was also shown that “industrial” impurities led to a decrease in the efficiency of energy conversion of solar cells to 2.34 %.

Bilayer CZTS/Si absorber for obtaining highly efficient CZTS solar cell

The good photovoltaic (PV) properties of Cu2ZnSnS4 (CZTS) and silicon (Si) can be used combinedly as a potential route for enhancing the efficiency of CZTS solar cell. In this work, a bilayer CZTS/Si absorber structure is presented to replace the conventional single CZTS absorber layer based solar cell. The numerical tool SCAPS-1D is utilized first to validate the structure with the help of J-V characteristics, generation rate, quantum efficiency and band diagrams. A similar tool is used afterwards to optimize the proposed structure considering different parameters such as layer thickness, defect density, carrier concentration and operating temperature. The highest yielded efficiency of the bilayer structure is 18.30% (VOC = 0.883 V, JSC = 25.90 mA/cm2). The thickness of both CZTS and Si layers are optimized and its effect on the performance parameters are discussed. The p-type doping concentrations of both layers are studied for the suitable range and optimized. Also, the electric field at the CZTS/Si interface is estimated. Next, the defect state density and operating temperature are varied to see the solar cell performances. The studied results provide a clear indication of the performance improvement of the CZTS solar cell using the bilayer CZTS/Si absorber structure.

Interface Recombination of Cu2ZnSnS4 Solar Cells Leveraged by High Carrier Density and Interface Defects

Kesterite Cu2ZnSnS4 (CZTS) solar cell has emerged as one of the most promising thin‐film photovoltaic technologies that allows for cheap, clean, and efficient renewable power in the future. Nevertheless, limited by the large photovoltage deficit caused by severe interface recombination, the potential of CZTS solar cells is far from being fully tapped. Herein, it is demonstrated that the carrier density of the CZTS absorber and the acceptor‐like interface defects are two critical factors governing the interface recombination in addition to the unfavorable conduction band alignment. Results of device simulation suggest that passivating the acceptor‐like interface defects combined with appropriate absorber carrier density is the essential way to promote the photovoltage and efficiency of CZTS solar cells to a more competitive level. It is believed that these results could be generally applicable to the interface recombination of other heterojunction solar cells.

Band alignment tuning at Mo/CZTS back contact interface through surface oxidation states control of Mo substrate

The molybdenum (Mo) back contact is one of the crucial factor that affects the performance of kesterite Cu2ZnSnS4 (CZTS) thin film solar cells. Thick MoS2 which is formed during sulfurization process of CZTS is known to be harmful for the device performance. MoOx on surface of Mo substrate with proper thickness can enhance the efficiency of CZTS solar cells through reducing the thickness of MoS2 layer and tailoring the work function of back contact. However, the role of oxidation states of Mo in MoOx on the performance of solar cells is unclear. Herein the effect of MoOx with different oxidation states on CZTS absorber and intermediate MoS2 layer were investigated. Our results shown that the efficiency of CZTS solar cells on Mo substrate with proper surface oxidation status (MoO2.03) can be as high as 2.86 times of the one fabricated on higher oxidized Mo (MoO2.21), although the thinnest MoS2 layer was present in the latter case. This work discloses the origin of the oxidation states of Mo for the efficiency enhancement of kesterite structured solar cells. The results will be also helpful to improve the performance of compound semiconductor by oxidation states control strategy.

Efficiency enhancement of CZTS solar cells using structural engineering

We numerically performs structural engineering for lowering interfacial recombination, and enhancing efficiency of CZTS solar cells. Structural modification of controlling carrier density profile at CZTS/CdS interfaces, CZTS absorber surface region carrier density, CZTS surface region bandgap modification, Fermi level pining and tunneling at the CZTS/CdS junction are studied for their impact device performance. We observed that the lowering hole concentration and widening bandgap of CZTS in vicinity of CZTS/CdS junction, lower interface recombination and improve performance. Fermi level pinning near to conduction band edge at CZTS/CdS interface showed lower recombination as compared to the case where Fermi level is pinned at midgap at CZTS/CdS interface. The donor defects from buffer layer pins the Fermi level near conduction band and acceptor defect from absorber CZTS layer pins Fermi level near mid gap at CZTS/CdS interface. Intra band tunneling through high conduction band offset barrier maintain performance for up to 0.5 eV spike barrier. High hole density profile at CZTS/metal lower back contact interfacial recombination. These structural engineering numerical performed here, present bright aspect for improving efficiency of CZTS solar cells. • Device engineering is performed for controlling interfacial recombination in CZTS solar cells. • Absorber surface layer parameters such as carrier density profile and bangap influence interfacial recombination. • Fermi level pinning near conduction band edge is advantageous than Fermi level pinned at midgap at CZTS/CdS interface. • High majority carrier concentration near back contact in CZTS minimize the effect of high Schottky barrier and high SRV.

Improvement of Cu2ZnSnS4 thin film performance by using oxygen-containing Cu-Zn-Sn precursor

The CZTS thin film fabricated based on Cu-Zn-Sn (CZT) or Cu-Zn-Sn-S precursors have difficulties in making a pinhole-free and flat CZTS thin film. In this paper, Cu2ZnSnS4(CZTS) thin films were fabricated based on oxygen-containing Cu-Zn-Sn precursors. By intentionally introducing O into Cu-Zn-Sn precursors, sudden volume expansion from precursor to CZTS thin films can be avoided and smooth CZTS film surfaces without pinholes were produced. Oxygen-containing Cu-Zn-Sn precursors were prepared by sputtering ZnO, Cu, and Sn targets successfully. MoS2 formation could be suppressed by introducing ZnO as a barrier layer between CZTS absorber and Mo back contact interface during the sulfurizing process under high sulphur pressure. The short circuit current density (Jsc) and open circuit voltage (Voc) of CZTS solar cells could be increased by optimizing the sulfurization temperature. And the best conversion efficiency of CZTS solar cells from oxygen-containing precursors was 4.97 %, with an open circuit voltage of 566 mV, a short circuit current density of 21.44 mA/cm-2 and a fill factor of 41 %.

Effect of Prefabricated Layer Structure on Properties of CZTS Thin Films and Solar Cells

Cu2ZnSnS4 (CZTS) thin films based on single-layer and double-layer prefabricated layer structure were prepared on substrates by two-step method. The influence of prefabricated layer structure on the surface morphology, element composition and photoelectric properties of CZTS thin film was studied. The crystal structure, surface morphology and composition of the films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), respectively. The experimental results showed that the CZTS thin film with double-layer prefabricated structure had larger grain size, better crystallization and uniform distribution of film components than the CZTS thin film with single-layer prefabricated structure. The conversion efficiency of CZTS solar cells based on the double-layer prefabricated structure increased from 0.25% of the single-layer prefabricated structure to 3.05%. Therefore, the double-layer prefabricated structure CZTS thin film was more suitable as the absorption layer of CZTS thin film solar cells.

Effects of ethyl acetate additive on Cu2ZnSnS4 solar cells fabricated with a facile dimethylformamide-based solution coating process

The solution based on dimethylformamide (DMF) has shown promising application prospects in the fabrication of high-efficiency Cu2ZnSnS4 solar cells. However, due to the high boiling temperature of the solvent, it is difficult to completely volatilize DMF during the evaporation process after spin coating, leading to remains of C and O atoms at grain boundaries, which severely restricts the photoelectric performance of solar cells. In this study, ethyl acetate (EA) with green character was used as an additive to optimize the film formation process of DMF-based CZTS precursor. The experimental results showed that using a small amount of EA additives could effectively improve morphology, crystallinity, composition distribution and electrical properties of the CZTS absorber. In addition, the CZTS and CdS heterojunctions exhibited a cliff-like energy band structure, and the optimized conduction band offset increased the activation energy required for the carrier recombination path, consequently reducing the carrier recombination. Compared with the pure DMF precursor solution, the photoelectric conversion efficiency of CZTS solar cells with an EA addition ratio of 10% was improved by 42%, and the open circuit voltage of the device reached 601 mV.

Recent Development in Earth-Abundant Kesterite Materials and Their Applications

Kesterite Cu2ZnSnS4 (CZTS) has attracted attention as an earth-abundant alternative to commercially successful CIGS solar cells. CZTS exhibits decent optoelectrical properties while having excellent stability on top of being an earth-abundant, low-cost and non-toxic material. Therefore, in recent years, there has been a significant research effort to develop CZTS-based devices. The efficiency of CZTS solar cells reached 12.6% in 2013, and this was a remarkable achievement at the time. However, the efficiency of these devices has been stagnant since then while emerging technologies, most notably perovskite solar cells, keep breaking record after record. Currently, CZTS research focuses on discovering the secrets of material properties that hinder the efficiency of CZTS solar cells while branching out to develop alternative applications for this material. In this review, we summarize the interesting properties of CZTS as well as its promising applications, which include thin-film solar cells, charge-transfer layers in perovskite solar cells, and photoelectrochemical water splitting while briefly commenting on its other possible applications.

Effect of ZnS nanowire ARC on CZTS/CdS thin film solar cell by Nebulizer Spray Pyrolysis Technique

The main intention of this experimental work is to eliminate the reflection of the CZTS/CdS thin film solar cell by depositing the ZnS Antireflection coating (ARC) by Nebulizer Spray Pyrolysis Technique. The CZTS/CdS thin films with and without ZnS Antireflection coating (ARC) deposited using nebulizer spray pyrolysis method is reported in this work. The prepared films were characterized by X-ray diffraction, scanning electron microscopy and UV–Vis spectroscopy analysis. Structural parameters such as lattice constants, texture orientation factor, micro strain, dislocation density and crystallite size were estimated using XRD data. The efficiency of CZTS/CdS solar cell is calculated using I-V characteristics. The experimental results exhibit the short circuit current increased from 9.269 × 10−5A to 1.250 × 10−4A and efficiency raised from 0.21% to o.45%. with ZnS as a ARC. The theoretical quantum efficiency of CZTS solar cell with ZnS ARC is increased from 0.020% to 0.030%. The results indicates that the ZnS ARC is one of the perfect ARC in the CZTS solar cell.

Numerical analysis of potential buffer layer for Cu2ZnSnS4 (CZTS) solar cells

In this work, CZTS solar cell with heterojunctions CdS/CZTS and ZnS/CZTS have been simulated using the Solar Cell Capacitance Simulator (SCAPS-1D). The effect of thickness and doping concentration on the performances of both structures has been investigated. It is obtained that the optimum thickness is about 30 nm and the best doping concentration is around 5E16 cm−3 and 5E17 cm−3 for CdS/CZTS and ZnS/CZTS structures respectively. By using the buffer layers optimum parameters (thickness and doping concentration), the electrical efficiency of CZTS solar cell is boosted from 12.03 % to 12.38 % for CdS/CZTS structure and from 12.51 % to 12.78 % for ZnS/CZTS structure. The obtained results reveal some valued insights for manufacturing Cd_free CZTS solar cells.

Effect of CZTS/CdS interfaces deposited with sputtering and CBD methods on Voc deficit and efficiency of CZTS solar cells

The mechanism of VOC deficit in CZTS solar cell has been systematically investigated by depositing the CdS buffer layer with sputtering (SP) and chemical bath deposition (CBD), respectively. It was found that SP-CdS film exhibits larger crystallite size and more densely packed morphology than CBD-CdS film. The average optical transmittance of SP-CdS films deposited at 250 °C is 71.5% (74.6% at 450 °C), evidently higher than 50.2% of CBD-CdS film at 70 °C. However, CZTS solar cell with CBD-CdS shows less Voc deficit and higher conversion efficiency. By virtue of Hall and TEM measurements, the mechanism is further revealed: i) CdS can diffuse into CZTS layer easily and form a shallow n-type layer by CBD method. ii) CBD-CdS possesses high resistivity and tends to form colloidal, which can block pin-holes and type I voids between the grain boundaries. All of them improve the CZTS/CdS interface and raise the value of Rsh, and reduce the Voc deficit and boost the conversion efficiency. By optimizing the stoichiometric ratio of Cu/Sn and Zn/Sn, the best conversion efficiency of CZTS solar cells with CBD-CdS is beyond 8.2% (active area) without MgF2 anti-reflection coating.

Effect of ZnO Intermediate Layer Thickness on Performance of Cu2ZnSnS4 Solar Cells

Cu2ZnSnS4 (CZTS) thin films were sputtered on Mo/glass substrates using Cu, Sn and ZnS targets and sulfurized at 570°C. The effect of a ZnO intermediate layer between CZTS and Mo on the microstructure, morphology and photovoltaic properties was investigated. Three samples with different ZnO thickness, named as S1 (10 nm), S2 (50 nm) and S3 (211 nm), had the identical composition ratio of Cu/(Zn + Sn) = 0.67 and Zn/Sn = 1.05 for kesterite structure. No obvious secondary phase such as SnS, SnS2 and ZnS was found. XRD showed no ZnO peak which indicated that the ZnO layer was completely sulfurized and converted to ZnS and CZTS. The ZnO intermediate layer significantly inhibited the formation of MoS2 and the decomposition of CZTS. A porous interlayer with many voids appeared at CZTS/Mo in S1 and S2 which originated from two different formations of CZTS and resulted in the inferior properties. The efficiency of CZTS solar cells without ZnO was only 2.7%, obviously below that of the three samples with ZnO. The Voc and Jsc of S3 was 625 mV and 12.6 mA cm−2 respectively, which resulted in the highest efficiency of 4.16% in three samples. The results in S3 illustrate that the ZnS layer was substituted completely by ZnO which can effectively improve CZTS/Mo contact and the photovoltaic properties.

Ab‐Initio Investigation of the Band Alignment Between Cu2ZnSnS4 and Different Buffer Materials (Al2ZnO4, CeO2, ZnSnO3)

Limited efficiency of Cu2ZnSnS4 (CZTS) solar cells due to high recombination rates at the CZTS–buffer interface calls for alternative buffer materials to enhance the open circuit voltage and, therefore, the device performance. By means of ab‐initio hybrid functional calculations, the authors investigate the interfaces between the p‐type absorber CZTS and the n‐type buffer materials Al2ZnO4, CeO2, or ZnSnO3 to evaluate the band alignment. Strong hole confinement is predicted for the CZTS/Al2ZnO4 and CZTS/ZnSnO3 interfaces. A small conduction band offset of 0.31 eV is obtained for the CZTS/ZnSnO3 interface, indicating that ZnSnO3 should be considered for improving the efficiency of CZTS solar cells.

Contribution to improve the performances of Cu2ZnSnS4 thin-film solar cell via a back surface field layer

In this research work, SCAPS-1D simulator is used to model and investigate the CZTS (Cu2ZnSnS4) solar cells. A substrate cell structure ZnO/CdS/CZTS/Mo was used as a base model. A novel structure is proposed in which a back surface field (BSF) layer is inserted in order to improve the solar cell performances. A CZTS layer has been added as BSF layer. The obtained results present an increase in efficiency of CZTS solar cell from 12.03% to 14.03%. An optimization of different physical parameters (Thickness and doping concentration) of BSF layer has been done, the improvement on the electrical parameters of the solar cell was achieved (ƞ = 14.16%, Voc = 0.997 Volt, Jsc = 24.63mA/cm2 and FF = 57.65%) according to 1E18 cm−3 value of doping concentration and 0.1 μm thickness, the enhancing in the electrical efficiency is about 17.70%. The optimum value of BSF layer thickness is considered as 70 nm according to 1E18cm−3 of doping concentration with a conversion efficiency of 14.11% under 1.5 AMG illuminations, which corresponding to following electrical parameters: Jsc = 24.57 mA/cm2, Voc = 0.988 Volt, and fill factor = 58.06%. Also, at the end, the effect of the BSF layer on the band diagram and the generation-recombination profiles of CZTS solar cell is discussed.

Thermal effect on CZTS solar cells in different process of ZnO/ITO window layer fabrication

In this work, a window layer consisting of zinc oxide (ZnO) and indium‑tin-oxide (ITO) thin films was prepared by sputtering under different heat treatment processes (in-situ or post annealing) to study the effect on structural ordering and performance of Cu2ZnSnS4 (CZTS) solar cells. It is found that all characteristic performance parameters including open circuit voltage (Voc), short circuit current density (Jsc), fill factor (FF) and efficiency of CZTS solar cells were improved for the window layer with ITO thickness = 350 nm post-annealed at lower temperature. Specifically, Voc of the CZTS device was increased by 57 mV when the window layer was post-annealed at 200 °C (Voc = 585 mV) compared to the device with window layer made at 300 °C (Voc = 528 mV). We further reduced the thickness of the window layer with ITO thickness = 140 nm which was deposited in an in-situ annealing process at 220 °C. Compared to the 350 nm thick film made by post-annealing, it is found that the thin film made by in-situ annealing help to further boost the Voc (equals 635 mV) and thus efficiency (3.20%) of CZTS solar cells. Study of the evolution of full width half maximum (FWHM) and intensity ratio (Q) of major Raman scattering peaks of CZTS indicates a much reduced structure disorder in the CZTS material with ZnO/ITO window layer annealed at low temperature. Further analysis of the evolution of diode ideality factor (A), reverse saturation current density (J0) and Urbach energy (Eu) of these devices revealed that the quality of bulk CZTS and/or CZTS/CdS heterojunction were more degraded at higher temperature. However, the in-situ annealing provided extra benefits to device performance which is possibly due to modification of interfacial properties of CZTS/CdS and/or CdS/ZnO.