Towards High-Efficiency Inverted CH3NH3GeI3 Perovskite Solar Cells

The performance of inverted CH3NH3GeI3 (MAGeI3) perovskite solar cells incorporating both a hole transport layer (HTL) and an electron transport layer (ETL) was investigated using the Solar Cell Capacitance Simulator (SCAPS). Three candidate HTLs, including PEDOT:PSS, MoS2, and WS2, along with five ETLs including PCBM, TiO2, IGZO, ZnO, and SnO2, have been systematically evaluated. The analysis shows that WS2 and SnO2 provided the most favorable hole and electron transport, respectively. To improve device efficiency, the absorber layer thickness, defect density in MAGeI3, doping levels of WS2 and SnO2, as well as the interface defect densities and the work function of indium tin oxide (ITO), have been systematically studied. The optimal absorber layer thickness is determined to be approximately 900 nm. The optimal doping density of both WS2 and SnO2 is 1 × 1019 cm−3. The MAGeI3 layer should maintain a defect density as low as 1 × 1015 cm−3, and the defect densities at MAGeI3 interfaces should remain at 1 × 1015 cm−2. Additionally, an ITO work function of at least 5.2 eV is necessary to prevent the formation of a Schottky barrier at the ITO/WS2 interface. The simulated power conversion efficiency (PCE) can reach 22.9% under these optimized conditions. Our simulation results offer a viable route to develop high-efficiency MAGeI3 perovskite solar cells.