Engineering and Electrical Behavior of Au/CuI/CsGeI3/CsSnI3/ZnSe/FTO Perovskite Solar Cells: Numerical Studies by Scaps and DFT

Abstract

This study evaluates the potential of the lead-free double perovskites CsGeI₃ and CsSnI₃ for high-performance photovoltaic applications through a combined approach integrating SCAPS–1D solar cell modeling with density functional theory (DFT). Using the Au/CuI/CsGeI₃/CsSnI₃/ZnSe/FTO device configuration, SCAPS–1D simulations identified optimal absorber-layer parameters, including thicknesses of 1000 nm for CsGeI₃ and 700 nm for CsSnI₃, a doping level of 1019 cm⁻³, and a defect density of 1014 cm⁻³. Under these optimized conditions, the device achieved high performance, delivering a Voc of 1.17534 V, Jsc of 30.54 mA·cm⁻² FF of 88.08%, and a PCE of 31.61%. To complement these device-level results, DFT calculations were performed to examine the structural, mechanical, thermodynamic, and electronic characteristics of both materials. The optimized lattice parameters, elastic constants, and derived mechanical moduli confirmed structural integrity and ductile behavior, while the calculated sound velocities and Debye temperatures supported their thermal stability. Electronic-structure analyses revealed narrow mBJ band gaps of 0.71 eV for CsGeI₃ and 0.69 eV for CsSnI₃, indicating strong absorption capabilities across the visible-NIR region. This work presents the first application of a CsGeI₃-CsSnI₃ dual-absorber solar cell, offering a promising strategy for improving light absorption, carrier transport, and overall device performance. Furthermore, these combined results demonstrate that CsGeI₃ and CsSnI₃ possess favorable optoelectronic properties and high simulated photovoltaic efficiency, making them excellent candidates for future eco-friendly solar-energy technologies.