Abstract: CsPbI_2.85Br_0.15 is a promising inorganic perovskite solar cell (IPSCs) material with excellent photo - thermal stability. However, the high defect state density on the surface of the film as a non-radiative recombination center causes a serious open circuit voltage loss (V_loss), which limits the improvement of PCE (Power Conversion Efficiency). In this paper, the surface of CsPbI_2.85Br_0.15 film was modified with 1, 8-octylenediamine hydroiodate (ODADI), and the iodide in ODADI was used to fill the iodide atomic vacancy (V_I), which effectively inhibited the ion migration. Finally, the N-I-P device based on air spin coating achieves the champion efficiency of 19.46%, and the device stability is also improved to a certain extent.