Abstract The morphology of perovskite film plays a key role in determining photoabsorption, carrier transport and ambient stability in perovskite solar cells. However, due to the fast crystallization kinetics, the perovskite film fabricated by solution-processing technique usually suffers from low crystallinity and poor orientation. Here, both the morphology and the ambient stability of perovskite films were improved through regulating crystallization rate and enhancing intermolecular interaction by adding α, ω-diamino poly (ethylene glycol) (PEG-NH2) into precursor solution (mixture of CH3NH3I and PbCl2). The PEG-NH2 and Pb2+ tended to form a new chelated compound Pb2+-PEG-NH2. The stable multidentate chelation between Pb2+ and PEG-NH2 retarded the crystal growth rate to half of the one of the film without PEG-NH2, which is determined by the in situ UV–vis absorption spectra and in situ two-dimensional detection capability. The slow crystallization process is beneficial for realizing an uniform perovskite film with enhanced crystallinity almost 3 times of the pristine film, and increased crystal size from smaller than 100 nm to larger than 300 nm. In addition, the content of perovskite crystals adopted (h 0 0) orientation increased from 9.59% to 20.70% due to the flexible PEG-NH2 chains. Moreover, the ambient stability of perovskite films was also enhanced because the Pb-halogen bond in perovskite crystals became stronger as well as the film became defect-free. As a result, the device fabricated with PEG-NH2 attained a high efficiency of 15.6% with remarkably prolonged ambient stability without encapsulation. This work demonstrates that introducing the polymer that can coordinate to Pb2+ is a feasible way to simultaneously enhance both efficiency and stability of perovskite solar cells.