Germanium-lead double absorber layer perovskite solar cells: Further performance enhancement from the perspective of device simulation

Organic-inorganic metal halide perovskites are widely used in solar cells, but the toxic metal Pb2+ is still a necessary element to ensure excellent photovoltaic properties, so it is urgent to accomplish the conversion to low toxic perovskite solar cells. In this work, by introducing MAGeI3 to form a double absorber layer structure with MAPbI3, a novel germanium-lead perovskite solar cell is presented for the first time. Based on the conditional data matching the experimentally reported results, we simulated the device numerically with SCAPS-1D (Solar Cell Capacitor Simulator). Considering the interfacial recombination that exists between the surfaces of the various layers, interface defect layers (IDL1 and IDL2) were added on both sides of the absorber layer respectively. By adjusting the critical parameters including the thickness of IDL and the absorber layer, defect density, electron affinity, band gap, and operating temperature of the device, the influence of various factors on the cell performance was comprehensively analyzed and optimized. The results demonstrate that the optimum values for IDL1 and IDL2 thicknesses are 10 nm and 1 nm, respectively. When the defect density of IDL2 exceeds 1016 cm-3, the optoelectronic properties of the device deteriorate significantly. Appropriately increasing the doping concentration of the absorber layer can enhance the built-in electric field of the device. In addition, by studying the different electron transport layers, we found an interesting phenomenon that the conduction band of the as-designed material is negatively correlated with the VOC of the cell. Benefiting from the above-optimized performance, germanium-lead perovskite solar cells achieved an outstanding efficiency of 27.67% and the fill factor is 90.32%. MAGeI3/MAPbI3 double absorber layer structure ameliorates light absorption characteristics and stability of the device, while significantly reducing the toxicity of lead. This work provides a novel approach for realizing highly efficient and stable perovskite solar cells.