Effects of heterofunctional alkali-metal formate doping on perovskite solar cell performance

Various internal and external defects present in the perovskite film are one of the main factors that cause low efficiency and stability, and in order to realize high-performance perovskite solar cells, it is necessary to develop a method to effectively suppress them. In this study, a heterofunctional dopants strategy was attempted to integrate the effect of alkali metal cations (Rb⁺ and K⁺) and formate anion (HCOO¯) through doping engineering with alkali-metal formates, i.e., rubidium formate (RbHCOO) and potassium formate (KHCOO). Inclusive physical and photoelectric analysis revealed that doping with a small amount of alkali-metal formate leads to crystal growth and reduction of grain boundaries, and further passivates or inhibits bulk and surface defects. As a result, the photogenerated charge recombination was reduced and the charge carrier transport was improved, leading to improved PSC performance. RbHCOO-doped inverted planar PSCs achieved a PCE of up to 20.41% with long-term stability. Our findings provide a way for producing high-quality perovskite films with low defect densities that are essential for realizing high-performance PSCs.