The Impact of PbI2:KI Alloys on the Performance of Sequentially Deposited Perovskite Solar Cells

As univalent cation to the ammonium ions, alkali metal ions become vital alternatives or additives for the A-site ions of lead halide perovskites. They were reported to construct new perovskite structures or bring new features like reduced defect density, suppressed hysteresis, improved power conversion efficiencies (PCEs), stability, etc. In this work, by making an alloyed film of PbI 2 :KI in the first step of the sequential deposition, we find that a low concentration of KI can improve the roughness and microstructure of the PbI 2 film, facilitating the intercalation of ammonium salt into PbI 2 . In comparison, a higher concentration of KI will lead to the formation of K 2 PbI 4 clusters, resulting in perovskite films with decreased quality and high V OC loss in devices. The best-performing device based on one PbI 2 :KI alloy shows an enhanced PCE from 19.60 % to 21.18 %. The study can provide a referential insight into the influence of K + on the formation of perovskite films and the performance of corresponding devices. Graphical In recent years, alkali metal ions have been widely exploited to optimize the performance of perovskite solar cells. This work aims to explore the effect of potassium in the form of PbI 2 :KI alloy on perovskite solar cells. A high-quality perovskite film was fabricated by a two-step method, of which making PbI 2 :KI alloy was the first step. It achieved a power conversion efficiency of 19.60 % to 21.18 %.