Triggering the Passivation Effect of Potassium Doping in Mixed-Cation Mixed-Halide Perovskite by Light Illumination

Potassium (K+) doping has been recently discovered as an effective route to suppress hysteresis and improve the performance stability of perovskite solar cells. However, the mechanism of these K+ doping effects is still under debate, and rationalization of the improved performance in these perovskites is needed. Herein, the photoluminescence (PL) properties and device performance of mixed-cation mixed-halide perovskite are dynamically monitored with and without K+ doping under bias light illumination via a confocal fluorescence microscope, together with ultrafast transient absorption as well as time-dependent and time-resolved PL measurements. It is demonstrated that illumination is essential to trigger the passivation effect of K+ by forming KBr-like compounds, leading to the elimination of interface trapping defects and suppression of mobile ion migration, thus resulting in improved power conversion efficiency and negligible current-voltage hysteresis of solar cells. This work provides novel insight into the hysteresis suppression upon K+ doping and highlights the significance of light illumination when using this protocol.