In mesoscopic perovskite solar cells, the electron transport layer plays an important role in charge extraction and determines the charge-transport property to attain a superior photovoltaic performance. Herein, we report a low-cost, solution-based deposition procedure of decorating graphene quantum dots on the surface of mesoporous TiO2 film, expecting that a more effective electron-transport channel can be formed for the enhancement of solar cell performance, finally, an impressive power conversion efficiency of 20.45% is achieved in the resulting optimized perovskite solar cell. Furthermore, the results of various spectroscopic characterizations including electronic impedance spectroscopy, steady-state and time-resolved photoluminescence spectrum elucidate that the introduction of GQDs on the surface of mesoporous TiO2 film not only enhance the electron extraction but also facilitate the charge transportation at interface between the perovskite and electron transport layer.