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.