Device engineering of double perovskite based solar cells towards high-performance, eco-friendly solar cells

Conventional lead halide Perovskite Solar Cells (PSC) have toxicity and stability issues. Therefore it is crucial to look for lead-free inorganic perovskite material, such as La2NiMnO6, RbGeI3, CsGeI3, Cs2AgBiBr6 and others. There has been much work in the area of PSC using Cs2AgBiBr6 as an absorber, However, due to some critical issues of Cs2AgBiBr6, such as the film's broad bandgap which limits its capacity to absorb light, leading to corresponding PSC being typically restricted to around 4% efficiency. In this work, a lead-free PSC with Cs2AgBiBr6 as the absorber has been engineered to resolve the issues by considering the experimental works in the literature to increase efficiency to 6.3% from a maximum 4.48% as reported in the literature. The output response of both design approaches, as well as the potentiality of future designs, are investigated in terms of output parameters, i.e., Open-Circuit Voltage (V-OC), Short-circuit Current density (J(SC)), Fill Factor (FF), and Power Conversion Efficiency (PCE). Besides, this work also focuses on eliminating Sulphur from ETLs by working on several sulphides and oxide-based Electron Transport Layers (ETLs). Several solar cell device structures have been analyzed for their numerical simulation with sulphide ETLs such as ZnS, WS2, CdS, CdZnS and oxide ETLs such as TiO2, ZnO, WO3, IGZO. To progress towards eco-friendly PSCs, alternatives to sulphide, several transparent oxide alternatives (TiO2, ZnO, WO3, IGZO) have been considered as ETLs. These ETLs have been further doped with Mg to enhance the performance parameters. Mg-doped based ETLs additionally behaving as Hole-blocking layers (HBLs) in corresponding PSCs leads to comparatively significantly better performance in a number of aspects, including V-OC (1.21 V), PCE (5.74%), J(SC), and FF. The solar cell design has been optimized for high performance through various techniques such as varying ETL and absorber thickness, interface defects variation, series/shunt resistance, band to band recombination, and bandgap grading through doping. Also an effective electric field (E-eff) that depicts the conduction's impact has been calculated. Best performing device among different designs among PSCs with sulphide and oxide-based ETLs has been ZnS/Cs2AgBiBr6/Cu2O (PCE-6.3%) and Mg-doped (20%) ZnO/Cs2AgBiBr6/Cu2O (PCE-5.74%). These results may help researchers in their efforts to find the best-suited materials for the design of high-performance PSCs in the future.