Investigation of CsSnBr2Cl perovskite properties using first-principles GGA, PBE0, and HSE functionals and study of the photovoltaic characteristics of solar cells

Lead-free perovskite materials have recently been introduced as good photovoltaic materials for future applications due to their lower toxicity and environmental stability. In this research work, a study on the optoelectronic and photovoltaic properties of the mixed-halide perovskite compound CsSnBr₂Cl has been performed by utilizing the Density Functional Theory (DFT) approach along with device simulation techniques. The electronic structures of the studied compound are determined using DFT based on generalized gradient approximation (GGA), Perdew-Burke-Ernzerhof hybrid density functional theory (PBE0), and Heyd Scuseria-Ernzerhof (HSE) functionals. It is found that the studied compound is structurally and dynamically stable in accordance with its favorable tolerance factors, negative formation energy, and absence of imaginary vibrational frequencies. The compound possesses a semiconductor nature, and the PBE0 functional provides the closest band gaps to experimental values. Optical analysis, including Bethe–Salpeter Equation (BSE) calculations reveal strong excitonic effects and excellent light absorption in the visible region. Three distinct heterojunction systems were simulated using the Solar Cell Capacitance Simulator (SCAPS-1D) to investigate the photovoltaic properties. Among all the systems, the system consisting of FTO/C₆₀/CsSnBr₂Cl/CuSCN/Au exhibited the maximum Power Conversion Efficiency (PCE) value of 22.62% due to favorable energy alignment and charge carrier transportation characteristics. These performance metrics represent theoretical upper limits under idealized conditions, highlighting the material's potential for high-efficiency photovoltaics. The effect of absorber thickness on photovoltaic properties was studied by varying the absorber thickness between 0.8–1.6 µm. It is observed that the short-circuit current density increases with increasing thickness of the absorber layer, whereas open-circuit voltage and fill factor decrease due to increased recombination losses. In conclusion, this work presents an elaborate theory on the correlation between the material characteristics and photovoltaic behavior of solar cells based on lead-free CsSnBr₂Cl perovskite material.