By spin-coating method, a thin layer of dodecylamine hydroiodide (DAHI) is introduced to the surface of perovskite CH3NH3PbI xCl3- x. This layer of DAHI successfully changes the surface of perovskite from hydrophilic to hydrophobic as revealed by the water contact angle measurement. Significantly enhanced fluorescence intensity and prolonged fluorescence lifetime are found for these modified films in comparison to those of unmodified perovskite films, suggesting that the number of structure defects is reduced dramatically. The compatibility between the perovskite and hole transfer layer (HTL) is also improved, which leads to more efficient hole collection from the perovskite layer by HTL as revealed by the fluorescence spectra, fluorescence decay dynamics, as well as the transient photocurrent measurements. Moreover, the perovskite solar cells (PSCs) fabricated from these modified perovskite films exhibit significantly improved humidity stability as well as promoted photoelectron conversion efficiency (PCE). The result of this research reveals for the first time that the layer of aliphatic amino hydroiodide is a multiple functions layer, which can not only improve the humidity stability but also promote the performance of PSCs by reducing the defect number and improve the compatibility between perovskite and HTL. Because the structure of aliphatic amines can be functionalized with myriad of other groups, this perovskite modification method should be very promising in promoting the performance of PSCs.