Lead-free Ge-based perovskite solar cell incorporating TiO2 and Cu2O charge transport layers harnessing over 25% efficiency

In recent years, significant progress has been achieved in the field of perovskite solar cells (PSCs), particularly those comprised of organic–inorganic lead halides, resulting in a remarkable record efficiency of 25.20%. However, the persistent issue of lead toxicity poses a considerable barrier to their widespread commercial adoption. To address this challenge, this study focuses on the optimization of lead-free germanium-based halide PSCs using SCAPS-1D simulation software. In our investigation, CsGeI 3 serves as the absorber layer, TiO 2 functions as the electron transport layer (ETL), Cu 2 O is utilized as the hole transport layer (HTL), and various metals are employed as the back metal contact (BMC). The optimization of the BMC leads to the establishment of the FTO/TiO 2 /CsGeI 3 /Cu 2 O/Ni structure. Subsequent optimization steps include fine-tuning the thickness of the absorber, ETL, and HTL layers, as well as optimizing acceptor doping and defect density in the absorber and HTL layers. Sequentially, donor doping and defect density in the ETL are investigated. Interfacial defect densities, along with the impact of temperature, series resistance, and shunt resistance on the photovoltaic performance, are also considered. Upon completion of these optimization procedures, the final device exhibits notable performance characteristics, including an open-circuit voltage ( V OC ) of 1.165 V, fill factor (FF) of 88.52%, short-circuit current density ( J SC ) of 24.40 mA/cm 2 , and a power conversion efficiency (PCE) of 25.16%. Furthermore, the optimized structure without Cu 2 O HTL demonstrates impressive performance, yielding a PCE of 25.15%. The outcomes presented in this study hold promise for the development of advanced lead-free PSCs, paving the way for high conversion efficiencies in future solar energy technologies.