A theoretical study of all-inorganic perovskite solar cells: Computational modeling of the CsPbI3/RbGeI3 bilayer absorber structure

All-inorganic perovskite solar cells (AI-PSCs) have garnered significant attention in the perovskite community due to their stability and efficient photogeneration and absorption capabilities. Despite the toxicity associated with all-inorganic CsPbI3 perovskites containing lead (Pb), its presence remains crucial for achieving excellent photovoltaic properties. However, the imperative shift towards AI-PSCs using less toxic materials with suitable photovoltaic properties is imperative. The incorporation of a double perovskite absorber layer allows for broadening the absorption spectrum of PSCs and enhancing cell stability. In this study, we propose a novel AI-PSC structure with CsPbI3 as the top absorber with a wide bandgap of 1.69 eV and a lead-free RbGeI3 perovskite as the bottom absorber layer with a low bandgap of 1.31 eV. Utilizing numerical simulations with the SCAPS-1D simulator, we analyze the photovoltaic parameters of AI-PSCs with single and double absorber layers. Our investigations reveal that a double absorber layer structure, comprising CsPbI3 and RbGeI3 materials, outperforms a single-junction PSC based on CsPbI3. By optimizing critical device parameters, we achieved an impressive efficiency of 31.91% in an AI-PSC device with a CsPbI3(0.6 μm)/RbGeI3(2 μm) bilayer configuration. This study positions lead-free RbGeI3 perovskite as a promising partner for CsPbI3, offering a potential pathway for the development of highly efficient AI-PSCs.