Numerical simulation and proof of concept for performance assessment of cesium based lead-free wide-bandgap halide solar cells

Perovskite solar cells (PSCs) which utilize hybrid lead halide perovskite (CH3NH3PbI3) as a light absorber layer and exhibit some unique optoelectronic properties so have been emerging as fast-growing photovoltaic technology. However, lead halide-based perovskite has some challenges like stability and toxicity, which create an opportunity to investigate new materials. Lead-free halide perovskite remains a top contender for a possible replacement for these lead halide perovskites. Accordingly, this work mainly focusses on cesium (Cs) based leadfree halide perovskite solar cells which contain two different lead-free halides namely Cs2AgBi0.75Sb0.25Br6 wide bandgap halide 1 (WBH1) and Cs2AgBiBr6 wide bandgap halide 2 (WBH2). The bandgap of WBH1 and WBH2 is 1.82eV and 2.01eV, respectively. Detailed investigation of WBH1 and WBH2 based perovskite solar cells have been carried out to explore the efficiency potential of these devices. As a part of the complete research effort, device performance is optimized in terms of absorber layer thickness variation and by using different electron transport layer (ETL) and hole transport layer (HTL). During absorber layer thickness optimization, SpiroOMeTAD and TiO2 are used as HTL and ETL respectively for both WBH1 and WBH2 based PSCs. Both WBH1 and WBH2 based solar cell with 300 nm absorber layer thickness reflected peak PV performance. WBH1 and WBH2 based solar cells reflected 12.39% and 8.43% conversion efficiency with TiO2 (ETL)/Cu2O (HTL) and MZO (ETL)/Cu2O (HTL), respectively. Results are analyzed using the energy band diagram, the current density-voltage (J-V) curve and external quantum efficiency (EQE). Studies carried out over here in this work may open up the window for the development of non-toxic, lead-free perovskite-based solar cell and help in exploring this field even more deeply.