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

The inclusion of potassium in perovskite solar cells (PSCs) has been widely demonstrated to enhance the power conversion efficiency and eliminate the hysteresis effect. However, the effects of the locations K⁺ cations on the charge-carrier dynamics remain unknown with respect to achieving a more delicate passivation design for perovskite interfaces and bulk films. Herein, we employ the combined electrical and ultrafast dynamics analysis for the perovskite film to distinguish the effects of bulk doping and interfacial passivation of the potassium cation. Transient absorption spectroscopy indicates an enhancement of charge-carrier diffusion for K⁺-doped PSCs (from 808 to 605 ps), and charge-carrier transfer is significantly promoted by K⁺ interface passivation (from 12.34 to 1.23 ps) compared with that of the pristine sample. Importantly, K⁺ doping can suppress the formation of wide bandgap perovskite phases (e.g., FAPbI_0.6Br_2.4 and FAPbI_1.05Br_1.95) that generate an energy barrier on the charge-carrier transport channel.