Boosting the performance of perovskite solar cells through a novel active passivation method

Potassium halides have recently garnered much attention, due to their improvement of perovskite solar cell performance. A small amount of potassium halide incorporated in a perovskite absorber is able to provide advantages in terms of crystallinity, light absorption and trap state reduction. Here, we present a potassium chloride (KCl) pretreatment process to fabricate high-efficiency perovskite solar cells (PSCs). A KCl layer was inserted at the SnO2/MAPbI(3-x)Cl(x) interface via a simple spin coating method. It is observed that potassium cations (K+) and chloride anions (Cl-) diffused into the perovskite film during the thermal annealing process. The diffusion of K+ and Cl- will stop when they reach a bulk defect, resulting in an active passivation effect. It is verified that the incorporation of KCl enhances the crystal perfection and light absorption of the perovskite film. The average power conversion efficiency (PCE) of PSCs increases from 16.62% to 17.81%, with a leading PCE of 19.44%.