The effect of B-site doping in all-inorganic CsPbI_xBr_3-x absorbers on the performance and stability of perovskite photovoltaics

Despite the impressive efficiency of perovskite solar cells (PSCs), their operational stability is still hindered by the thermodynamic instability of the hybrid organic-inorganic absorber layer with ABX(3) structure (A: organic/inorganic cation, B: metal cation, X: halogen anion and mixtures thereof). Due to the hygroscopic and volatile nature of the organic cations, i.e., methylammonium (MA(+)), they show very poor stability not only against thermal stress but also moisture. Therefore, a photoactive material free from organic components could offer great opportunities to prolong the operational stability of devices. In this context, all inorganic CsPbIxBr3-x perovskites are meticulously developed in terms of their structural/thermal stability and have triggered increasing research interest due to great prospects in the commercialization of perovskite technology. However, besides relatively low performance, the poor phase stability of inorganic perovskites associated with lattice strain and vacancies still requires a thorough understanding and permanent solutions for tackling these problems. In this comprehensive review, the recently reported B-site doping strategy in inorganic CsPbIxBr3-x perovskite thin films, which has been elucidated to passivate the defects, tune the grain orientation, and enhance the lifetime of charge-carriers, is presented based on different B-site elements belonging to group IIIA, IVA and VA, alkaline-earth, transition, and lanthanide metals. Solutions for confronting these current problems are elaborated and an outlook on further strategies is given.