Perovskite materials, most notably organo-lead iodide species, have recently demonstrated great potential in future high-performance photovoltaics. Formamidinium lead iodide perovskite (FAPbI3) features desirable bandgap and thermal resistance, and has thus emerged as the most promising candidate among the perovskite family for highly efficient photovoltaic devices. However, the photoactive black-phase FAPbI3 is not energetically favorable at room temperature. Polytype formation and other intermediate non-photoactive phases can readily occur, which undermines the photovoltaic performance. Through multimodal in-situ monitoring of the perovskite crystallization process, we found an oriented nucleation mechanism that acted as the key to avoid undesirable phases. This concept was applicable to improving the photovoltaic device performance under different film-processing scenarios. In this talk, I will present our recent progress on improving the stablity and efficiency of FA-based perovskites, and the potential of the commercialization will be discussed.