Integration of SCAPS-1D and density functional theory for the performance evaluation of RbGeI3-based perovskite solar cell

The instability of organic-inorganic perovskites in the presence of heat, light, or moisture coupled with the presence of carcinogenic lead (Pb) motivated researchers to look for alternatives in the form of Pb-free all-inorganic perovskite materials as potential absorbers for designing stable and efficient solar cells. In this study, SCAPS-1D is utilized to study the photovoltaic performance of all-inorganic Pb-free RbGeI₃-based planar n-i-p perovskite solar cell (PSC). The optoelectronic characteristics of RbGeI₃ are obtained using WIEN2K within the density functional theory framework. Twenty-five different combinations of RbGeI₃-based device architectures with different ETLs and HTLs are explored out of which the best PSC architecture is chosen for further analysis. We show that the device structure FTO/TiO₂/RbGeI₃/PTAA/Au exhibited a remarkable power conversion efficiency (PCE) of 24.03 %, a high fill factor (FF) of 79.85 %, an open circuit voltage (V_oc) of 0.88 V, and a short circuit current density (J_sc) of 33.83 mA/cm². Enhanced optimized performance characteristic is obtained through the variation of the defect density, bandgap, and thickness of the RbGeI₃ layer. This paper proposes a new way of studying the photovoltaic characteristics of lead-free perovskite absorbers.