A path to sustainable, non-toxic solar cell technologies: Exploring Cs-based halide perovskites with optimized HTLs and ETLs through SCAPS-1D and DFT studies

Abstract

This research investigates the capability of cesium-based, non-toxic perovskite solar cells (PSCs) incorporating germanium (Ge) and tin (Sn) from Group 14 elements, combined with halogens (F, Cl, Br, I). The aim is to evaluate the structural stability, environmental safety, and photovoltaic performance of 24 Cs-based perovskite configurations while excluding toxic, unstable, or radioactive elements. Through a combination of Density Functional Theory (DFT) and SCAPS-1D simulations, we analysed key optical properties such as absorption coefficient, reflectivity, conductivity, refractive index, and dielectric function. Our study identified Cs₂SnBr₆, Cs₂TiBr₆, and Cs₂TiI₆ as optimal candidates due to their favourable bandgaps, offering efficient light absorption and enhanced stability. In particular, Cs₂TiI₆ stands out due to its superior optical properties compared to other absorbing layers. Cs₂TiI₆ also demonstrated excellent performance when paired with optimized hole transport (HTL) and electron transport layers (ETL), specifically Copper Tin Sulphide (Cu₂FeSnS₄)- CFTS as the HTL and WS₂ as the ETL, resulting in improved photovoltaic efficiency. The optimized device exhibited a V_OC of 0.78 V, a J_SC of 45.93 mA/cm², a fill factor of 85.53 %, and a power conversion efficiency of 30.58 %, demonstrating a very good photovoltaic performance. These findings provide a strong foundation for developing high performance, sustainable, and non-toxicity PSCs.