A-site engineering in Ge-based lead-free perovskites for high-efficiency solar cells

Abstract

Lead toxicity restrains the scaling of lead halide perovskites, hence sparking a quest for lead-free alternatives. In this study, AGeI₃ perovskites were modeled as an absorber in a perovskite solar cell under SCAPS-1D simulation. In a device with ZnOS as the ETL, CBTS as the HTL, and the optimized device structure ITO/ZnOS/AGeI₃/CBTS/Au, AGeI₃ perovskites with Cs, FA, Rb, and MA as the A cation were investigated, and the CsGeI₃ perovskite produced a cell with a V_oc of 1.4452 V, a J_sc of 24.237 mA cm⁻², a FF of 87.85%, and a PCE of 30.77%, while RbGeI₃ gave the next best PCE of 30.09%. For the optimization of the device performance, the absorber layer thickness was adjusted to 0.9 µm, and the defect density was maintained at 10¹² cm⁻³. The ETL and HTL thicknesses were kept constant at 0.05 µm and 0.5 µm, respectively. The defect density of the ETL and HTL was maintained at 10¹⁴ cm⁻³, while the interface defect density was maintained at 10¹¹ cm⁻². During the optimization of the device performance, the following physical parameters were varied: layer thickness, doping, bulk and interface defects, series and shunt resistances, and temperature. The simulations showed how individual carrier transport mechanisms, recombination profiles, and J–V and QE characteristics, as well as differences in the metal work functions, are used in the perovskite structure.