Differentiated Functions of Potassium Interface Passivation andDoping on Charge-Carrier Dynamics in Perovskite Solar Cells

The inclusion of potassium in perovskite solar cells (PSCs) has been widelydemonstrated to enhance the power conversion efficiency and eliminate the hysteresis effect.However, the effects of the locations K+cations on the charge-carrier dynamics remainunknown with respect to achieving a more delicate passivation design for perovskite interfacesand bulkfilms. Herein, we employ the combined electrical and ultrafast dynamics analysis forthe perovskitefilm to distinguish the effects of bulk doping and interfacial passivation of thepotassium cation. Transient absorption spectroscopy indicates an enhancement of charge-carrier diffusion for K+-doped PSCs (from 808 to 605 ps), and charge-carrier transfer issignificantly promoted by K+interface passivation (from 12.34 to 1.23 ps) compared with thatof the pristine sample. Importantly, K+doping can suppress the formation of wide bandgapperovskite phases (e.g., FAPbI0.6Br2.4and FAPbI1.05Br1.95) that generate an energy barrier onthe charge-carrier transport channel