Importance of CdS buffer layer thickness on Cu₂ZnSnS₄-based solar cell efficiency

Abstract

Cu 2 ZnSnS 4 (CZTS) thin films were grown on Mo-coated soda lime glass (SLG) substrates by the sulfurization of DC magnetron-sputtered Zn, Sn and Cu metallic precursors under a sulfur atmosphere at 550 °C for 45 min. Understanding the composition and structure of the CZTS absorber layer is necessary to obtain efficient solar cells. With this aim, x-ray diffractometry, Raman spectroscopy, scanning electron microscopy, energy dispersive spectroscopy and x-ray photoelectron spectroscopy were used to investigate the CZTS absorber layers. CZTS absorber films were obtained and found to be Cu-poor and Zn-rich in composition, which are both qualities desired for efficient solar cells. CdS was used as a buffer layer and was grown by the chemical bath deposition technique. The optical properties of CdS films on SLG were searched for using a spectroscopic ellipsometer and the results revealed that the bandgap increases with film thickness increment. CZTS-based solar cells with different CdS buffer layer thicknesses were prepared using a SLG/Mo/CZTS/CdS/ZnO/AZO solar cell configuration. The influence of the CdS buffer layer thickness on the performance of the CZTS solar cells was investigated. Device analysis showed that electrical characteristics of solar cells strongly depend on the buffer layer's thickness. Highly pronounced changes in V OC , fill factor and J SC parameters, which are the main efficiency limiting factors, with changing buffer layer thicknesses were observed. Our experiments confirmed that decreasing the CdS thickness improved the efficiency of CZTS solar cells down to the lowest thickness limit.

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

“…For CZTS solar cell, researchers are using different buffer layers such as CdS, ZnS and CdZnS [12]. Among them CdS turned out as a most potential buffer layer for CZTS solar cell, even though it has toxic component and wastage probability [13].…”

Solution-processed CZTS thin films and its simulation study for solar cell applications with ZnTe as the buffer layer

“…The performance of the modelled solar cell structure (ZnO:Al/ZnO/ZnTe/CZTS/Mo) was analysed via means of the cell parameters such as e ciency (η), short circuit current density (J SC ), open circuit voltage (V OC ), ll factor (FF) and quantum e ciency. The performance of proposed cell structure is found comparable with the standard solar cell structures (ZnO:Al/ZnO/CdS/CZTS/Mo) with CZTS as a harvesting layer (Jhuma et al 2019, Cantas et al 2018. These CZTS cells are conventionally fabricated using CdS, CdTe or CdZnS as the buffer layer which have toxic component, and it is expected to avoid the use of cadmium (Jhuma et al 2020).…”

“…The molybdenum substrate of thickness around 1mm, is overlaid by CZTS layer and further followed by the buffer layer of ZnTe; then window layer of ZnO with the thickness around 50nm and nally Al doped ZnO layer with thickness around 300 nm as transparent conducting oxide are considered. The designing of cell is taken from the conventionally fabricated solar cell structure (ZnO:Al/ZnO/CdS/CZTS/Mo) (Jhuma et al 2019, Cantas et al 2018), here CdS buffer layer is replaced with ZnTe. The detailed description of parameters used for simulation is shown in Table 1.…”

Effect of defects and secondary phases in Cu2ZnSnS4 absorber material on the performance of Zn(O,S) buffered devices

“…In addition to the disordered KS peak, Type 1 films also have peaks at around 286 and 338 cm −1 which are assigned to the main vibrational A symmetry modes of KS CZTS [54][55][56]. Presence of these peaks point out that the Type 1 CZTS films are mixture of disordered KS and KS phases, which is not very unusual for non-stoichiometric compositions [60]. Type 1 films also show peaks at around 257 cm −1 and 268 cm −1 which are attributed to the B mode of longitudinal optical vibration (B(LO)) and A vibration modes of KS CZTS, respectively [55,56,61].…”