Room Temperature Fabrication of SnO 2 Electrodes Enabling Barrier‐Free Electron Extraction for Efficient Flexible Perovskite Photovoltaics

Room temperature-processed electron transport layers (RT-ETLs) demonstrate vast potential to be used in fabricating high-performance flexible perovskite solar cells (PSCs) in an energy-saving manner. However, the RT-ETL normally suffers from inferior crystallinity, mismatched energy level, and high surface trap-state density, which would result in under-optimized interfacial electron extraction and undesirable interfacial charge recombination at ETL/perovskite interface, thus limiting the device performance. Herein, a novel strategy is demonstrated to prepare annealing-free RT-ETL based on precrystalline metal ion-modified SnO2 nanocrystals, which perfectly optimizes the interfacial energy level alignment between ETL and perovskite layer, achieving nearly zero-barrier charge transfer at the interface. As a result, the charge extraction has been remarkably accelerated and the interfacial charge recombination has been largely suppressed, leading to a ≈26% enhancement in device efficiency. The best-performing flexible PSCs achieve efficiencies up to 19.3%, accompanied by outstanding mechanical strength under repeated bending cycle tests, which, to the best of the knowledge, is one of the highest reported values for the flexible perovskite photovoltaics fabricated with RT-ETLs.