A vacuum deposition process has been developed to fabricate high efficiency perovskite solar cells with high stability using alternating layer-by-layer vacuum deposition. The new deposition process allows us to relax the strict deposition monitoring and control measures, while realizing superior uniformity in film morphology, surface coverage and smoothness, together with crystalline phase purity. The power conversion efficiencies for the planar device is as high as 21.5% on rigid glass substrate, the highest reported so far. More importantly, we have developed a superior low temperature TiO2 coating and transferred the cell fabrication process onto lightweight flexible polymeric substrate. The highest cell efficiency achieved is over 18.3%, it is also the highest efficiency among the flexible perovskite cells reported. Meanwhile, the devices show very good stability over long term exposure in ambient with very low degradation. After a representative cell was exposed in ambient lab condition for 1500 hours, its final cell efficiency is as high as over 91% of its initial efficiency with its degradation accounts for only smaller than 9%. Further analysis on the stability of the perovskite solar cells will be discussed.