ZrCl4 for energy level alignment at the perovskite/TiO2 interface

•Post-treatment of the electron transport layer with ZrCl4 in planar PSCs leads to enhanced short-circuit current.•Enhanced stabilized PCE is observed probably due to reduced charge accumulation at the interface.•UPS/XPS measurements reveal that energy band alignment between perovskite and transport layer is achieved and electrical experiments prove that charge extraction is facilitated.