Perovskite films are attracting much attention due to their excellent optoelectronic properties. The corresponding photovoltaic devices show a record efficiency of 25.7% since 2009, which is very promising to surpass silicon solar cells. The defects of the perovskite films are the major negative factors to achieve high efficiency. The defects of the perovskite films are related to the polycrystal nature of the perovskite films, which is unavoided and caused by the solution-based method. Therefore, high-quality perovskite films with fewer defects are very critical to obtain high-efficiency devices. One strategy is to incorporate some additives into the perovskite solutions to adjust the perovskite film growth toward fewer defects. However, the additives are very limited in this strategy and limited success is reported. The promising strategy is to passivate defects of the films after the film fabrication. We present the passivation of perovskite films by organic materials including polymers, organic small molecules as well as dye molecules. The organic molecules with the special organic functional groups interact with perovskite films to modify the defects of the films to improve the charge transport and reduce charge recombination, leading to improved device performance. The surface defects and the grain boundary defects of the perovskite films are passivated by the organic materials, which is confirmed by the electron/hole only devices, electronic impedance spectroscopy (EIS) studies, photoluminescence, and time-resolved photoluminescence. The device efficiency increases from ~19% to ~21%, which is manifested by the J-V measurements. The passivation mechanism of the devices by organic materials is investigated and demonstrated.