N-i-p Type perovskite solar cell generally requires air oxidation of Spiro-OMeTAD layer to achieve high power conversion efficiency (PCE).However,the detailed oxidation mechanism is still not fully understood.In this paper,oxidation of Spiro-OMeTAD was demonstrated via a non-contact electrochemical way using UV-Vis absorption,laser beam induced current (LBIC) imaging and secondary ion mass spectrometry (SIMS) profiling of the Spiro-OMeTAD films.At the cathode,oxygen reduces to form OH-with the help of H2O,while the anodic reaction is oxidation of Spiro-OMeTAD to form Spiro-OMeTAD+.Diffusion of Li+ towards surface of Ag electrode completes the electrochemical cycle and increases conductivity of hole-transporting layer.SIMS analyses on completed devices demonstrate that the oxidation of Spiro-OMeTAD also leads to migration of Li+ through the perovskite layer into SnO2,which supposedly leads to an increase of the built-in voltage.We verify those results by incorporation of the experimentally measured Li+ concentration into a numerical drift-diffusion simulation,to replicate solar cell J-V-curves.This work provides a new insight into the oxidation of Spiro-OMeTAD in the perovskite solar cells,and demonstrates that Li+ migration is involved in the oxidation of Spiro-OMeTAD.