Perovskite solar cells (PSCs) have attracted increasing attention with their high efficiency and low cost. However, their journey towards commercialization is currently hindered by the issues associated with degradations in the ambient environment and under other harsh conditions. These stability-related issues can be associated with several reasons such as halide vacancies, structural defects, ion migrations and others within the perovskite structures. Herein, we studied the effect of an oxygen-inducing strategy on metal halide perovskites to reduce their halide vacancies for stable solar cells. It was found that perovskite films with the precisely controlled oxygen amount show improved photovoltaic performances, including fill factor and open-circuit voltage, when utilized in solar cells. We showed that the presence of oxygen plays a crucial role in increasing the efficiency and stability of solar cells due to the improvements in the structural uniformity and grain size, and thus suppresses charge and nonradiative recombination. More importantly, the oxygen-induced α-FAPbI3-based PSCs retained nearly 50% of their initial efficiencies while the devices without oxygen maintained less than 10% of their initial values after harsh testing conditions, demonstrating excellent structural stability and water tolerance.