Integration of experimental and simulation approaches to optimize CdS buffer layers in CZTS based heterojunction solar cells

Abstract

An integrated approach of experimentation and numerical simulation were employed to investigate the influence of cadmium sulfide (CdS) buffer layer on the performance of CZTS based heterojunction solar cells. The effect of variation in deposition time with the properties of CdS and its role as the n-layer in CdS/CZTS devices has been investigated. The deposition time of CdS thin films were varied from 30 to 120 min using a cost-effective chemical bath deposition. To investigate properties of the films XRD, SEM, EDS, Raman, and UV–visible characterisations were carried. XRD analysis confirmed the presence of cubic-phase CdS with improved crystallinity, while SEM images showed a densely packed, boulder-like morphology. Additionally, EDS confirmed a stoichiometric Cd-to-S ratio. Film thickness found to increase from 160 to 400 nm, while bandgap slightly narrowed from 2.46 to 2.40 eV. Hall measurement showed improved n-type conductivity with deposition time. Heterojunctions devices of architecture < FTO/CdS/CZTS/Ag > were fabricated and their junction parameters are evaluated by using I-V measurements. Further, solar cell devices of the same structure were simulated using SCAPS-1D. The CdS layer deposited for 30 min yielded the best performance, with a simulated efficiency of 17%. This investigation suggests that deposition time of CdS film is a key parameter for optimizing photovoltaic devices.