Surface Passivation of Perovskite Solar Cells with Oxalic Acid: Increased Efficiency and Device Stability

Solution processed perovskite films usually exhibit numerous defect states on the surfaces of the films. Here in this work, oxalic acid (H₂ C₂ O₄ ), 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 H₂ C₂ O₄ 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 H₂ C₂ O₄ passivated perovskite film. After optimizing the H₂ C₂ O₄ 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.