Improving the Performance and Stability of Perovskite Solar Cells through Buried Interface Passivation Using Potassium Hydroxide

Charge carrier recombination caused by the buried interface defects in perovskite solar cells is widely accepted as a challenge that seriously degrades device performance and stability. Herein, we devise a facile method to passivate the buried titanium dioxide (TiO2)/perovskite interface using potassium hydroxide (KOH) through a wet chemical process. OH- and K+ can coordinate with the under-coordinated Ti and O on the TiO2 surface, respectively. Meanwhile, due to the strong interaction between K+ and Br-, Br- in the MAPbI(2.85)Br(0.15) perovskite would be attracted and thus migrate toward the TiO2/perovskite interface during the formation process. Hence, KOH can not only passivate the interface but also effectively glue the TiO2 electron transfer layer and the perovskite layer together to generate a tightly integrated interface, which effectively reduces interface defects. Moreover, KOH at the interface can mediate the nucleation process and promote the formation of the perovskite layer with less defects. Thus, improved charge carrier extraction and reduced nonradiative recombination are achieved. As a result, the perovskite solar cell with KOH interface passivation demonstrates an increase in power conversion efficiency from 17.12 to 19.19%, associated with a good improvement of stability.