Incorporation Mechanism of Potassium in FAPbI3 Perovskite Solar Cell Materials

We study the structural and electronic mechanisms of potassium (K+) incorporation in the FAPbI3 perovskite layer. The K+ ions in FAPbI3 perovskite solar cells lead to higher power conversion efficiency (PCE), lower trap density, and faster charge transfer. K+ eliminates the I–V hysteresis for 5% K-doped perovskite. Moreover, the phase stability is reduced by K+ incorporation. The enhancement in PCE and reduced stability are attributed to the passivation of deep-level charge traps and increased carrier mobility and lower phase change activation energy, respectively, and in all cases, KFA antisite formation is revealed, by density functional theory (DFT) calculations, to be the main source. KFA has reduced the electron–phonon coupling of charge transport and the activation energy barrier for the cubic-to-hexagonal phase transformation, which accelerates phase degradation. Our key findings will enable the future design and optimization of high-efficiency and stable mixed-perovskite solar cells.