Localized Oxidation Embellishing Strategy Enables High‐Performance Perovskite Solar Cells

Abstract 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 SnO 2 electron transport layer (ETL) has contributed the recent record power conversion efficiency (PCE) of the pero‐SCs, yet still suffers from surface defects of SnO 2 nanoparticles which brings energy loss and phase instability. Herein, we report a localized oxidation embellishing (LOE) strategy by applying (NH 4 ) 2 CrO 4 on the SnO 2 ETL. The LOE strategy builds up plentiful nano‐heterojunctions of p ‐Cr 2 O 3 / n ‐SnO 2 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 ‐FAPbI 3 with the SnO 2 ETL treated by the LOE strategy realized a PCE of 25.72 % (certified as 25.41 %), along with eminent stability performance of T 90 >700 h. This work provides a brand‐new view for defect modification of SnO 2 electron transport layer.