One of the challenges with organic-inorganic hybrid perovskite films, is its degradation from moisture present in ambient atmosphere, which severely restricts its crystallization process using thermal annealing in ambient air having high humidity levels. A widely used method for perovskite film crystallization is use of thermal annealing in inert atmosphere to rapidly crystallize the film in perovskite phase, immediately after its deposition. Herein, we have explored several methods of crystallization of mixed-halide perovskite (CH3NH3PbI3-xClx) film crystallization in ambient air with an aim to obtain high crystallinity and complete conversion to perovskite phase in ambient air assisted with and without thermal annealing. We optimized the crystallization process of perovskite film by exposing the film in ambient air, partially exposure to air followed by thermal annealing, exposing it to air-flow at room temperature. Perovskite films were spin coated inside the N2 filled glove box and immediately were taken outside in air with 40% relative humidity (RH). Crystallized mixed-halide perovskite films obtained from different approaches were then used to fabricate planar perovskite solar cells with device structure as ITO/PEDOT:PSS/CH3NH3PbI3-xClx/PC60BM/Rhodamine/Ag. It was concluded that humidity plays an important role in crystallization of perovskite films in ambient air, but additional treatment could lead to improved perovskite crystallinity.