Localized Oxidation Embellishing Strategy Enables High‐Performance Perovskite Solar Cells

Perovskite solar cell (pero‐SC) has attracted extensive studies as a promising photovoltaic technology, wherein the electron extraction and transfer exhibit pivotal effect to the device performance. The planar SnO2 electron transport layer (ETL) has contributed the recent record power conversion efficiency (PCE) of the pero‐SCs, yet still suffers from surface defects of SnO2 nanoparticles which brings energy loss and phase instability. Herein, we report a localized oxidation embellishing (LOE) strategy by applying (NH4)2CrO4 on the SnO2 ETL. The LOE strategy builds up plentiful nano‐heterojunctions of p‐Cr2O3/n‐SnO2 and the nano‐heterojunctions compensate the surface defects and realize benign energy alignment, which reduces surface non‐radiative recombination and voltage loss of the pero‐SCs. Meanwhile, the decrease of lattice mismatch released the lattice distortion and eliminated tensile stress, contributing to better stability of the devices. The pero‐SCs based on α‐FAPbI3 with the SnO2 ETL treated by the LOE strategy realized a PCE of 25.72% (certified as 25.41%), along with eminent stability performance of T90>700 h. This work provides a brand‐new view for defect modification of SnO2 electron transport layer.