Improved PCE in stable lead-free perovskite solar cells based on band engineering of ETL and absorber

In this paper, a unique structure of graded band gap (GBG) electron transport layer (ETL) based lead-free Perovskite solar cell (PSC) is proposed and numerically investigated. The structure consists of cesium Formamidinium tin iodide (FACsSnI 3 ) with band-gap grading aspect sandwiched between electron and hole transport layers. Various ETLs such as Zn(S,O), ZnO, ZnMgO and C60 have been considered and investigated with and without GBG aspect. It is revealed that the use of band engineering based on band gap grading ETL and absorber films allows the dual-advantages of enhanced photogeneration and carrier extraction mechanisms. The merits of the proposed PSC structure are compared to other published results in terms of improved photovoltaic parameters. The obtained results show improvements in photoconversion properties of the PSCs when GBG-Zn(S,O) is considered as an ETL. The effective conduction band alignment of GBG-Zn(S,O)/GBG-FACsSnI 3 heterostructure interface leads to an improved carrier collection efficiency and subsequently improved efficiency. The optimized PSC structure presents power conversion efficiency as high as 21.67 %, with an open circuit voltage of 0.96 V, short-circuit current of 30.75 mA/cm 2, and fill factor of 72.88%. The obtained photovoltaic parameters of the proposed GBG-ETL/GBG-FACsSnI 3 heterostructure can provide new perspectives for the realization of efficient cost-effective lead-free PSCs.