Numerical investigation of eco-friendly FASnI3 perovskite solar cells: Effects of energy band alignment and interface defect

Abstract

HC(NH₂)₂SnI₃ (FASnI₃) is considered as a promising lead-free perovskite (PVK) for its wide bandgap and great temperature stability. However, Sn-based perovskites exhibit lower electron affinities than Pb-based perovskites, resulting in large band mismatch at the interfaces. The energy band alignment and defects at the interfaces play an important role in the perovskite solar cell (PSC) performance. In this simulation, we optimize the FTO/TiO₂/FASnI₃/PTAA/Au structure to achieve efficiently and eco-friendly FASnI₃-based PSCs using SCAPS-1D, with a special focus on interface engineering. The band offsets of TiO₂/FASnI₃ and FASnI₃/PTAA interfaces are systematically modified by changing the electron affinity values of the absorber and charge transport layers (CTLs). Additionally, the influence of defect density at the TiO₂/FASnI₃ and FASnI₃/PTAA interface is also discussed. It is found that the efficiency of PSCs can be significantly improved by suitable energy band alignment accompanied by small spike-like band offsets and the reduction of interface defects. The initial structure is based on an experimental work with an efficiency of 2.53 %. After optimization, the device reaches the highest theoretical power conversion efficiency (PCE) of 17.92 % with fill factor (FF) of 77.79 %, open circuit voltage (V_oc) of 0.93 V and short circuit current density (J_sc) of 24.81 mA/cm².