One of the most important factors governing the photovoltaic efficiency and environmental stability of Perovskite Solar Cells (PSCs) is the quality of their perovskite films. However, the present study demonstrates that CH3NH3PbI3 perovskite films after anti-solvent washing are far from perfect on the surface, where the crystallization degree is quite low with complex multi-phases associated with numerous defects and notable chemical inhomogeneity. Herein, we report a novel anti-solvent washing treatment simply using Hydrogen Iodide (HI) additive in chlorobenzene (CB) which can enormously improve CH3NH3PbI3 films surface with high crystallization phase purity and chemical homogeneity, leading to excellent structural stability under humidity, heat and even tensile force. Based on such high quality films with defect-less surface, fabricated planar PSCs with an architecture of ITO/TiO2/CH3NH3PbI3/Spiro-OMeTAD/MoOx/Au present a champion PCE of 19.94% and improved stability under humidity. Moreover, fabricated flexible planar PSCs on PET/ITO substrates with a champion PCE of 17.32% are shown to be more robust under tensile force than their control devices. The present study thus not only provides more insight into the facile defects passivation process on the surface achieved via balancing halide ions, but also provides a practical but efficient treatment which can be widely used to fabricate high quality CH3NH3PbI3 films for environmentally stable high performance device applications.