Improving Sb2Se3 thin-film solar cell performance via stepwise optimization of a TiO2/CdS-coupled buffer layer

Abstract

Currently, most of the high-performance Sb₂Se₃ thin film solar cells (TFSCs) are coupled with a cadmium sulfide (CdS) buffer layer, which has proven effective in enhancing device performance. However, lower bandgap (2.4 eV), presence of shunt paths, and high surface roughness of CdS contribute to optical losses, recombination losses, and carrier extraction inefficiencies in TFSCs. To mitigate these problems, this study introduces an additional cadmium chloride (CdCl₂) treatment step to modify pristine CdS films deposited via standard chemical bath deposition (CBD). Furthermore, a titanium dioxide (TiO₂) intermediate layer is introduced beneath the CdCl₂-treated CdS buffer layer, using a simple spin-coating technique, to form a TiO₂/CdS-coupled buffer layer. The hydrothermal growth of the Sb₂Se₃ light absorber over these buffer layers was optimized to fabricate efficient FTO/TiO₂/CdS/Sb₂Se₃/Spiro-OMeTAD/Au structured solar cell devices. The fabricated devices with the pristine CdS, CdCl₂-treated CdS, and TiO₂/CdS (CdCl₂-treated) are denoted as BL1, BL2, and BL3, respectively. The optimized Sb₂Se₃ TFSC with BL3 reaches a power conversion efficiency (PCE) of 6.19 % which is significantly higher than the device with BL1 (PCE = ∼5.10 %). Furthermore, a surface topography conducted on buffer layers revealed the reduced roughness after CdCl₂ treatment and TiO₂ intermediate layer improved the interface quality. Additionally, the effect of the Sb₂Se₃ absorber thickness on the device performance was further investigated using the SCAPS-1D software tool. The champion devices with BL1 and BL2 retained ∼90 % of initial efficiency, meanwhile, the PCE of the device with BL3 improved when stored vacuum packed for 4 months.