Impact of interface defects and doping levels on bismuth-based double perovskite solar cells: a numerical modeling approach

As perovskite solar cell (PSC) technology nears commercialization, concerns about lead content and biodegradability remain significant. Lead-free double perovskite materials, like Cs₂AgBiBr₆, have garnered attention for their reduced toxicity and improved stability. Cs₂AgBiBr₆ perovskites, in particular, show promise for photovoltaic applications due to these benefits. In this paper, we propose the design and conduct numerical simulations of a double perovskite solar cell based on Cs₂AgBiBr₆, aiming to address the need for safer and more stable alternatives in PSC technology. The initial tested cell, derived from experimental work, features a hydrogenated Cs₂AgBiBr₆ layer with an unprecedented low bandgap of 1.64 eV. The cell structure, FTO/TiO₂/Cs₂AgBiBr₆/Spiro-OMeTAD/Metal back contact (Flat Band, φ_m = 5.18 eV), achieved a maximum power conversion efficiency (PCE) of 26.61%. It also recorded an open-circuit voltage (V_oc) of 1.58 V, a short-circuit current density (J_sc) of 20.98 mA/cm², and a fill factor (FF) of 80.10% at an optimal absorber layer thickness of 800 nm. Both bulk and interface defects were analyzed, revealing that optimizing the interface between the HTL and perovskite is more critical than the ETL/perovskite interface due to higher recombination current at the HTL/perovskite interface. Overall, the simulation results from this study provide valuable insights for designing environmentally friendly perovskite solar cells.