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.