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For low temperature (≤180 °C) processed perovskite solar cells (PSCs), SnO2 has been proven to be one of the most effective electron transporting layer. However, problems, such as poor electric conductivity and high defect density, inevitably exist in the SnO2 films which are fabricated using low temperature solution methods. Element doping of SnO2 film is a feasible strategy to alleviate the above problems. Herein, W doping of the SnO2 is realized through addition of ammonium tungstate hydrate into the molecular precursor of SnO2. The W doped SnO2 film exhibits higher conductivity, and can better extract and transport the electrons from the perovskite films. Hence, power conversion efficiency is boosted from 20.60 % for the reference PSCs to 21.83 % for PSCs fabricated on 2.5 mg mL−1 ammonium tungstate hydrate doped SnO2 films. [ABSTRACT FROM AUTHOR]

Solution processed perovskite films usually exhibit numerous defect states on the surfaces of the films. Here in this work, oxalic acid (H2C2O4), which has two C=O groups, is selected and used to passivate the surface defects of the two‐step deposited perovskite films via post‐treatment. Strong interaction between H2C2O4 molecule and the Pb2+ ions located on the surface of perovskite film has been confirmed via Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy, which can result in an effective suppress of the surface defects. Furthermore, time‐resolved PL spectrum indicates that carrier lifetime is prolonged in the H2C2O4 passivated perovskite film. After optimizing the H2C2O4 concentration, the target perovskite solar cells can demonstrate superior power conversion efficiencies (21.67 % from reverse measurement and 21.54 % from forward measurement) and superior device‐stability. [ABSTRACT FROM AUTHOR]