CZTS-based Thin Film Solar Cells Research Articles

MoS2 augmentation in CZTS solar cells: Detailed experimental and simulation analysis

This study investigates the optimization of CZTS-based thin-film solar cells through the incorporation of MoS2 as an interfacial layer. Using SCAPS-1D simulation software, we analyzed the effects of layer thicknesses, carrier concentrations, and defect densities on device performance. The optimized CZTS (100 nm)/ MoS2(1000 nm)/ CdS(100 nm)/ ZnO(50 nm) structure demonstrated a significant efficiency increase to 19.01 % compared to 17.03 % for the CZTS (1100 nm)/ CdS(100 nm)/ ZnO(50 nm) cell. Key improvements include enhanced charge generation, quantum efficiency, and balanced carrier transport.Materials were synthesized using microwave-assisted methods and characterized by XRD and UV–vis spectroscopy. XRD confirmed the desired crystal structures, while optical bandgaps of 1.5 eV (CZTS), 1.3 eV (MoS2), 2.4 eV (CdS), and 3.3 eV (ZnO) were determined. Practical solar cells were fabricated using spin-coating techniques, with thicknesses of CZTS (122 nm)/ MoS2 (1038 nm)/ CdS(130 nm)/ ZnO(94 nm). While showing improved performance with the MoS2 layer, efficiencies were lower than simulated values due to fabrication-related defects. The best experimental cell achieved 1.89 % efficiency, compared to 1.38 % without MoS2.This research demonstrates the potential of MoS2 as an effective interfacial layer in CZTS solar cells, providing insights into optimizing layer properties for enhanced performance. The study also highlights the challenges in translating simulated improvements to practical devices, emphasizing the need for advanced fabrication techniques to minimize defects and maximize efficiency.

Nitrogen doped single layer graphene for CZTS-based thin film solar cells

CdS thin films are commonly utilized as a buffer layer in chalcopyrite thin-film solar cells. However, due to the toxic nature of Cadmium (Cd), ongoing efforts are being directed towards exploring alternative options. In this contribution, doped graphene film with remarkable optical and electrical properties has been introduced for the first time as an alternative buffer layer, replacing CdS in CZTS thin-film solar cell application. In this study, nitrogen-doped graphene (N-doped graphene) film was utilized as a substitute buffer layer in the CZTS thin-film solar cell structure, replacing the conventional CdS thin film. For comparative analysis, CZTS/N-doped graphene and CZTS/CdS traditional solar cell structures were fabricated and separately characterized. The CZTS thin films produced were examined through EDX, XRD, SEM, Raman, optical transmission and PL spectroscopy measurements. According to performed analyses, the Cu-poor and Zn-rich kesterite CZTS thin films exhibited a uniform and dense polycrystalline microstructure as observed in surface and cross-sectional SEM images. XRD spectra of the kesterite CZTS thin film displayed predominant peaks corresponding to the (112), (220/204), and (312/116) diffraction planes of the kesterite CZTS phase. Raman spectra showed a dominant peak at ∼336 cm−1 associated with the kesterite CZTS phase. PL emission spectra indicated transitions from the conduction band to defect levels. The CVD-grown doped graphene film exhibited a 3.43 I2D/IG ratio and a 25 cm−1 FWHM of the 2D peak, indicating a single-layer graphene according to Raman analysis. Permanent nitrogen doping with a 2% atomic concentration was confirmed by XPS measurement. The optical transmission measurement of the single layer doped graphene film showed a 95% transmittance value. Nitrogen doping was contributed to decrease the sheet resistance of the graphene film. The Glass/Mo/CZTS/N-doped graphene/i-ZnO/ITO/Al solar cell displayed a VOC of 0.267 V, JSC of 24.6 mA/cm2, FF of 36.46, and η of 2.37%, showing higher FF and Jsc values but lower conversion efficiency compared to the Glass/Mo/CZTS/CdS/i-ZnO/ITO/Al traditional solar cell structure. Hence, the superior working function and transparency properties position the N-doped graphene film as a competitive buffer layer for use in CZTS-based thin-film solar cells.

Toward improving the performance of Cu2ZnSnS4-based solar cells with Zr, W or sulfurized layers at the SnO2:F/Cu2ZnSnS4 rear interface

The photovoltaic performance of Cu2ZnSnS4 (CZTS)-based thin film solar cells with transparent back contacts is mainly constrained by the ohmic loss due to degradation of the back contacts at high temperatures required for the growth of the CZTS absorbers. This work has attempted to use ultrathin Zr and W interlayers at the SnO2:F (FTO)/CZTS interface with the purpose of improving the ohmic properties of FTO and hence the performance of solar cells. 20 nm thick Zr and W layers were coated on FTO using direct current magnetron sputtering, followed by heating at 550 °C in a sulfur atmosphere for some of the samples. Inclusion of Zr and W interlayers compromised the transmittance of the FTO back contact, however heating of the samples in a sulfur atmosphere improved the transmittance to values comparable to or better than those of un-heated FTO. Furthermore, heated W/FTO showed a significant improvement in electrical conductivity as observed from Hall effect measurements. To make complete solar cells, CZTS absorber, buffer (CdS) and window (i-ZnO/ZnO:Al) layers were sequentially deposited on the un-heated FTO, Zr/FTO, W/FTO and Mo back contacts. Glow discharge optical emmision spectroscopy confirmed that Zr and W did not diffuse into the absorber and also prevented Na diffusion into the absorber. From the scanning electron microscopy cross sectional analysis, an impovement in the absober grain size and a clear junction between the absorber and FTO with W interlayer were observed. Grazing incident X-ray diffractometry confirmed the polycrystalline nature of the CZTS thin films and indicated the presence of other phases, particularly SnS2. On the resulting solar cell parameters, the inclusion of a W interlayer reduced the series resistance from 4.5 Ωcm to 3.7 Ωcm2. An improvement in short circuit current density (JSC) is also observed, enhancing the efficiency of the solar cells with CZTS/W/FTO to 3.1 % compared to that with CZTS/Mo at 2.7 % and CZTS/FTO at 3.0 %. W was found to improve the external quantum efficiency response and JSC of the solar cells for both backside and frontside light illumination. On the other hand, inclusion of a Zr interlayer (Zr/FTO) only slighlty improved the open circuit voltage, but compromised the JSC compared to FTO and W/FTO back contacts. Thus, the findings of this study demonstrate the prospect for improving the performance of the CZTS-based thin film solar cells through the inclusion of ultrathin Zr and W interlayers between the FTO back contact and CZTS absorber.

Enhancing the open-circuit voltage and efficiency of CZTS thin-film solar cells via band-offset engineering

Limits on the conversion efficiency and open-circuit voltage lead to low kesterite thin-film solar cell performance. The conduction band offset (CBO) between the absorber and buffer layers (p-CZTS and n-CdS) is considered to be one of the effective factors for the performance of these devices. The simulation results demonstrated that the optimal thickness and doping concentration for obtaining a high performance in the solar cell which is based on CZTS/CdS absorber/buffer layers would respectively be 50 nm and 1.5 × 1017 cm−3. The CBO at absorber/buffer interface plays a significant role in solar cell performance and the highest CZTS-based solar cell efficiency is obtained within the range of − 0.4 eV and + 0.4 eV of the CBO. Solar cell performance decreases from 5.12 to about 3% when the positive CBO increases from 0.4 to 0.7 eV. Moreover, the impact of CBO on device quantum efficiency was investigated. The optical response range changed with an increase in + ΔEC and the highest value (about 80%) was observed in visible and near ultraviolet light within the range of 400–520 nm. In − ΔEC, electrons can be transferred from the buffer layer to the window layer and the optical photons proportional to the buffer layer’s band gap help generate free electrons and holes, which cause a slower reduction of the quantum efficiency within the negative offsets and the above-mentioned range, through electric field bending. In addition, a large number of n-type materials such as CdS, SnS2, ZnO, ZnTe, ZnS, Zn(O, S), (Mg, Zn)O, In2S3, TiO2, and CdTe were analyzed as buffer layers in CZTS-based thin-film solar cell. The CZTS-based thin-film solar cells with SnS2, ZnO0.55S0.45, ZnO0.80S0.20, and Mg0.2Zn0.8O led to a conversion efficiency of about 13%. Furthermore, an open-circuit voltage of above 700 mV was obtained by using ZnO0.40S0.60 and Mg0.1Zn0.9O buffer layers. By introducing the CZTSe/CZTS absorber layer and SnS2 buffer layer in the structure of the proposed solar cell, the best efficiency and open-circuit voltage is deduced as 16.28% and 780 mV, respectively.

Fabrication of CZTSSe Thin Film Solar Cell By Single Step Sulfo-Selenization of Stacked Metal Precursors

The Cu2ZnSn(S,Se)4 (CZTSSe) thin films are the most promising photovoltaic absorber to replace CIGS, because it is comprised of abundant and inexpensive elements, and have a very high absorption coefficient of over 104 cm−1 with a direct bandgap energy. The theoretical solar conversion efficiency of CZTS-based thin film solar cells is as high as 32.2%. However, the maximum conversion efficiencies reported for electrical characteristics of devices based on these materials are still far from those accomplished more grown CIGS technologies. In order to achieve the efficiency of 20 % or more required for commercial technology, it is necessary to understand the limiting factors of the CZTSSe thin film. A parameter impacting the performance of increasing photovoltaic efficiencies in CZTSSe solar cells is band gap control of absorber through the control of S/(S+Se) ratio of CZTSSe thin films. Most of reported synthesized CZTSSe with high efficiency, the chalcogen composition of the absorption layer was controlled to optimize the characteristics. Most of them explain only the role of S in controlling the band gap in the CZTSSe thin film. It also only describes the characteristics of CZTSSe thin films and devices with different S ratios. However, S element plays another important role in CZTSSe crystal growth process. In this work, we have discussed the different effects of S in the CZTSSe thin film synthesis process. We fabricated CZTSSe thin films using optimized SLG-Mo/Zn/Cu/Sn (MZCT) as a stack structure and described the volatilization phenomenon of Zn element using MZCT stack structure. In addition, we have introduced H2S gas to effectively control the S/(S+Se) of the film in the sulfo-selenization process and to suppress the volatilization of Zn. The S injection process using H2S gas is more uniform and reproducible than any other processes. Unlike the pure selenization process, it was confirmed that a stable ZnSSe thin film was formed on the surface of the precursor during the sulfo-selenization process. The formation of ZnSSe thin film inhibited the volatilization of Zn, which facilitated the control of thin-film stoichiometry and also played an important role in crystal growth. Finally, the characteristics of thin films and devices fabricated through the optimization process are discussed. Acknowledge: This work was supported by the DGIST R&D Program of the Ministry of Science and ICT (19-BD-05) and the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry & Energy(MOTIE) of the Republic of Korea (No. 20173010012980).

Synthesis and optical characterization of n-ZnO and p-Cu2ZnSnS4 nanocrystalline thin films for low cost solar cells

High quality ZnO/Cu2ZnSnS4 thin films as a window/absorber layers were successfully synthesized via spin coating the sol-gel precursor of each composition without using any vacuum facilities. In this study, the impact of annealing temperature (400 °C, 3 h) on the ZnO window layer and different thickness (3 and 5 layers) of the Cu2ZnSnS4 (CZTS) absorber layer were investigated. X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), scanning electron microscope (SEM) and UV–vis–NIR spectroscopy were used for the structural, compositional, morphological and optical absorption analysis of each layer. ZnO exhibits wurtzite hexagonal crystal structure with particle size equals to 8.60 and 28.59 nm for fresh and annealed films, respectively. Micro-strain and dislocations density decreased with the annealing temperature. X-ray diffraction patterns for CZTS films show small peak at (112) according to the kesterite structure with particle size in nano-scale for the two thicknesses. ZnO films demonstrated direct optical band gap of 3.23 and 3.21 eV for fresh and annealed films, respectively. CZTS films (3 and 5 layers) also have direct optical band with optimum value (1.51 eV) for thickness of 5 layers. The J-V characteristics of the CZTS-based thin film solar cells (CZTS/ZnO/ZnO:Ag) were measured under air mass AM 1.5 and 100 mW/cm2 illumination. The values of the short circuit current (Jsc), open circuit voltage (Voc) and fill factor (FF) also have been obtained.

Sputter grown sub-micrometer thick Cu2ZnSnS4 thin film for photovoltaic device application

Structural properties and solar cells performance of sputter grown sub-micrometer thick (~600nm) Cu2ZnSnS4 (CZTS) films are investigated for low cost and large scale photovoltaic deployment. The CZTS films are deposited using single quaternary stoichiometric target at room temperature. X-ray diffraction, micro-Raman spectroscopy, and scanning electron microscopy measurements were carried out to investigate the structural property and secondary phase formation. The intense phonon peak at 334cm−1 in the visible Raman spectra confirms the deposition of single phase CZTS films. CZTS-based thin film solar cells show excellent performance with open circuit voltage ~600mV and over all cell efficiency of ~3.07%, exhibiting commercial potential toward large scale fabrication of photovoltaic devices.

Fabrication of an efficient electrodeposited Cu2ZnSnS4-based solar cells with more than 6% conversion efficiency using a sprayed Ga-doped ZnO window layer

Cost effective non-vacuum sprayed GZO layer was utilized in electrodeposited CZTS-based thin film solar cells for the first time. The thus-obtained solar device presented an appreciable conversion efficiency of 6.43%.

Development of Kesterite Cu2ZnSn(S1-x,Sex)4 (CZTSS)-Based Thin Film Solar Cells with In and Ga Free Absorber Materials

Chalcogenide-based semiconductors, such as CuInSe2, CuGaSe2, Cu(In,Ga)Se2 (CIGS), and CdTe have attracted considerable interest as efficient materials in thin film solar cells (TFSCs). Currently, CIGS and CdTe TFSCs have demonstrated the highest power conversion efficiency (PCE) of over 11% in module production. However, commercialized CIGS and CdTe TFSCs have some limitations due to the scarcity of In, Ga, and Te and the environmental issues associated with Cd and Se. Recently, kesterite CZTS, which is one of the In- and Ga- free absorber materials, has been attracted considerable attention as a new candidate for use as an absorber material in thin film solar cells. The CZTS-based absorber material has outstanding characteristics such as band gap energy of 1.0 eV to 1.5 eV, high absorption coefficient on the order of 104cm-1, and high theoretical conversion efficiency of 32.2% in thin film solar cells. Despite these promising characteristics, research into CZTS-based thin film solar cells is still incomprehensive and related reports are quite few compared to those for CIGS thin film solar cells, which show high efficiency of over 20%. The recent development of kesterite-based CZTS thin film solar cells is summarized in this work. The new challenges for enhanced performance in CZTS thin films are examined and prospective issues are addressed as well.

6% Efficiency Cu2ZnSnS4-based thin film solar cells using oxide precursors by open atmosphere type CVD

An open atmosphere type chemical vapor deposition (OA-CVD) method is one of the most effective methods for producing functional thin films. Especially, the OA-CVD method is a unique technique which is able to deposit metal oxide thin films by decomposition of vaporized raw materials released through a nozzle onto substrates in the air. Cu2ZnSnS4 (CZTS)-based thin films as absorber layers of thin film solar cells were fabricated by sulfurizing oxide precursor thin films synthesized by the OA-CVD method. Cu(C5H7O2)2, Zn(C5H7O2)2 and Sn(C5H7O2)2 were used as raw materials. The oxide precursor thin films were sulfurized at 520–560 °C in 5 vol% H2S balanced with N2. The formed CZTS-based thin films included oxygen with the composition ratio of O/(S + O) = 0.17–0.27 according to energy dispersive X-ray spectroscopy. The thin film solar cells using the CZTS-based thin films including oxygen [CZT(S,O) films] as the absorber layers were fabricated. The CZT(S,O) thin film solar cell had a stack structure of Al/Al-doped-ZnO/CdS/CZT(S,O)/Mo/soda-lime glass substrate. The efficiency of the CZT(S,O) thin film solar cells was 6.03%, which was the high efficiency in the reported value for CZTS-based thin film solar cells using oxide thin film precursors. It was found that the OA-CVD method is suited to fabricate the absorber layers of thin film solar cells.

The Influence of the Composition Ratio on CZTS-based Thin Film Solar Cells

AbstractCu2ZnSnS4 (CZTS) thin films were fabricated by using three RF co-sputtering continued with sulfurization method. The new type of thin film solar cells using CZTS as an absorber consists of buffer-layer and window-layer on CZTS films that were fabricated on a Mo-coated Soda Lime Glass (SLG) substrate. It was confirmed that CZTS solar cells with high conversion efficiency existed in a relatively narrow composition region. In this paper, the fabrication method of CZTS-based thin film solar cells in our laboratory was stated briefly and the influence of the composition ratio on the photovoltaic properties were presented. Furthermore, the properties of a genuine non-toxic solar cell using a Cd-free buffer-layer were introduced.

Development of CZTS-based thin film solar cells

The low cost, environmental harmless Cu 2ZnSnS 4 (CZTS)-based thin film solar cells are fabricated by using abundant materials. The CZTS film possesses promising characteristic optical properties; band-gap energy of about 1.5 eV and large absorption coefficient in the order of 10 4 cm − 1 . All constituents of this CZTS film, which are abundant in the crust of the earth, are non-toxic. Therefore, if we can use CZTS film practically as the absorber of solar cells, we will be free from both of the resource saving problem and the environmental pollution. In our CZTS project, CZTS absorber films were prepared by two independent techniques. One is three rf sources co-sputtering followed by annealing in sulfurized atmosphere. The latest conversion efficiency of over 6.7% was achieved by this technique. The other is co-evaporation technique. CZTS films were grown on Si (100) by vacuum co-evaporation using elemental Cu, Sn, S and binary ZnS as sources. XRD patterns indicated that the polycrystalline growth was suppressed and the orientational growth was relatively induced in a film grown at higher temperatures. In this presentation, the development of CZTS-based thin film solar cells will be surveyed.

Cu 2ZnSnS 4 thin film solar cells

Aiming to develop the solar cells free from the environmental contaminants, promising solar cell of a thin film type could be produced by using Cu 2ZnSnS 4 (CZTS) film as the absorber. The CZTS film possesses promising characteristic optical properties; band gap energy of about 1.5 eV and large absorption coefficient in the order of 10 4 cm −1, which means large possibility of commercial production of the most suitable absorber by using the CZTS film. In addition, as the CZTS film contains neither rare metals nor toxic materials, combining this film with Cd-free buffer layer, we can expect coming solar cells with nontoxic thin films in the near future. CZTS thin films were able to be produced successfully in our previous work by vapor phase sulfurization of the stacked precursors that were prepared by sequential vacuum evaporation of Cu, Sn, and ZnS. The best conversion efficiency with the heterojunction of ZnO:Al/CdS and CZTS was 5.45%, which showed the possibility of a very low cost solar cell. It has been, however, quite difficult to prepare CZTS film with high reproducibility. This paper showed the photovoltaic properties of CZTS-based thin film solar cells fabricated by using three types of precursors: (1) the conventional precursor with stacked layers of Cu/Sn/ZnS, (2) the modified precursor with the stacking order of Sn/Cu/ZnS, and (3) the precursor with five periods of Cu/SnS 2/ZnS, which was produced to increase the amount of S and to enhance the interdiffusion in precursor.