Investigation of efficient all-inorganic HTL-free CsGeI3 perovskite solar cells by device simulation

Organic-inorganic metal halide perovskite solar cells have achieved impressive results in the past dozen years. However, the unstable organic components methylamine (MA), formamidine (FA), and expensive hole transport layer (HTL) materials (Spiro-OMeTAD) have been stumbling blocks to their commercial development. In this work, an all-inorganic HTL-free CsGeI3 perovskite solar cell is constructed. In order to explore the internal influencing factors of the device as well as suitable materials, we numerically simulated the device with SCAPS-1D (Solar Cell Capacitor Simulator). The research demonstrates that when ZnOS is used as the electron transport layer (ETL), the generated energy band offset forms a recess structure, which makes the device exhibit excellent performance. Then, the effects of different metal back electrodes on HTL-free structure perovskite solar cells are explored, and the results indicate that when W is used as the metal back electrode, a potential barrier of 0.3 eV is formed between the metal back electrode and the absorber layer, effectively preventing carrier recombination. The critical parameters of the device including thickness, defect density, doping concentration, band gap, and electron affinity are optimized, based on which the optimum power conversion efficiency (PCE) of the proposed device structure (FTO/ZnOS/CsGeI3/W) reaches up to 26.70%, significantly improving the performance of germanium-based perovskite solar cells while reducing the cost. This work would provide a new avenue for realizing inorganic, low-cost, and efficient germanium-based perovskite solar cells.