First principles study to investigate structural, optical properties and bandgap engineering of XSnI₃(X=Rb, K, Tl, Cs) materials for solar cell applications

The PBE-GGA (Perdew Burke-Ernzerhof Generalized Gradient Approximation) for the exchange-correlation potentials, based on first-principles density functional theory (DFT) study is used to investigate the structural, optical, and electrical aspects of XSnI₃ (X = Rb, K, Tl, and Cs) materials. According to the DFT calculation, the energy band gaps (E_g) of XSnI₃ (X = Rb, K, Tl, and Cs) materials are 2.76, 2.01, 1.90, and 0.34 eV respectively. The direct energy bandgap (E_g) indicates that halide perovskite materials are appropriate semiconductors for solar cell application. A thorough analysis of optical conductivity indicates that, the optical conductance peaks of XSnI₃ (X = Rb, K, Tl, and Cs) halide perovskite materials reach maximum values of 2.3, 2.2, 4.5, and 5.2 eV, respectively, in the ultraviolet spectrum and shift slightly at higher energy bands. The maximal optical conductivity of XSnI₃ (X = Rb, K, Tl, and Cs) materials were (1.6 × 10⁵ Ω⁻¹ cm⁻¹, 1.8 × 10⁵ Ω⁻¹) cm⁻¹, 2.2 × 10⁵ Ω⁻¹ cm⁻¹ and 2.4 × 10⁵ Ω⁻¹ cm⁻¹ respectively. The XSnI₃ (X = Rb, K, Tl, and Cs) is a group of materials with enhanced surface area for light photon absorption and enhanced optical conductivity, energy absorption, and refractive index properties make them suitable for perovskite solar cell application.