Organic-inorganic hybrid perovskite solar cells have been widely recognized as an excellent candidate for next-generation photovoltaic devices because of their easy processing and rapidly developing power conversion efficiency (PCE). Owing to the fact that the interface is sensitive to photoelectric conversion properties, many strategies are used to improve the interface wettability between perovskite precursor solution and the hole transport layer (HTL). In this study, we report a method of argon plasma treatment on the poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) layer which could effectively enhance the wettability because of the improvement in the chemical compositions and film morphologies of PEDOT:PSS. In contrast to untreated films, the wettability of PEDOT:PSS is increased by 3.3, 3.6 and 3.7 times based on the optimization of plasma power, treating time, and pressure, respectively. We also systematically described the timeliness of wettability from 0 to 8 hours after plasma treatment. The interface wettability shows a down trend with increasing storage time.