Interfacial band offset engineering with barium-doping towards enhanced performance of all inorganic CsPbI₂Br perovskite solar cells

This study investigates the incorporation of Ba²⁺ at a low concentration into CsPbI₂Br, resulting in the formation of mixed CsPb_1−xBa_xI₂Br perovskite films. Photovoltaic devices utilizing these Ba-doped CsPbI₂Br (Ba-CsPbI₂Br) perovskite films achieved a higher stabilized power conversion efficiency of 14.07% compared to 11.60% for pure CsPbI₂Br films. First-principles density functional theory calculations indicate that the improved device performance can be attributed to the efficient transport of conduction electrons across the interface between Ba-CsPbI₂Br and the TiO₂ electron transporting layer (ETL). The Ba-CsPbI₂Br/TiO₂ interface exhibits a type-II staggered band alignment with a smaller conduction band offset (CBO) of 0.25 eV, in contrast to the CsPbI₂Br/TiO₂ interface with a CBO of 0.48 eV. The reduced CBO at the Ba-CsPbI₂Br/TiO₂ interface diminishes the barrier for conduction electrons to transfer from the Ba-CsPbI₂Br layer to the TiO₂ layer, facilitating efficient charge transport.