Hybrid perovskites have recently seen an unprecedented improvement in the power conversion efficiency in photovoltaics devices, and therefore are very promising materials for developing efficient and low-cost single junction solar cells [1-3]. However, a critical issue is the limited understanding of the correlation between the degree of crystallinity and the emergent perovskite/hole (or electron) transport layer on device performance as well as photo-stability. Los Alamos National laboratory (LANL) developed an efficient growth procedure for 3D halide perovskites in inverted perovskite cell architecture using PEDOT-PSS as a p-type hole transporting material (HTM) [4]. The initial collaboration between FOTON/ISCR and LANL led to the observation of a reversible self-healing mechanism under light soaking [5] and showed that the aging of the precursor solution plays a role in the nucleation of the perovskite crystallites [6]. In this study, we show that growth of methylammonium lead perovskites (MAPbI3) on nickel oxide (NiO) HTM, results in the formation of ordered and crystalline thin-films with enhanced crystallinity, leading to characteristic XRD Bragg peak width reminiscent of exclusively observed in the tetragonal phase in single-crystals. Photo-physical and interface sensitive measurements reveal a reduced trap density at the MAPbI3 perovskite/NiO interface in comparison with perovskites grown on PEDOT: PSS. Photovoltaic cells exhibit a high open circuit voltage (1.12 V), indicating a nearideal energy band-alignment. Moreover, we observe photo-stability of photovoltaic devices up to 10- Suns, which is a direct result of the enhanced crystallinity of perovskite thin-films on NiO. These results elucidate the critical role of the quality of the perovskite/HTL interface in rendering highperformance and photo-stable optoelectronic devices [7]. [1] Lee, M. M., Teuscher, J., Miyasaka, T., Murakami, T. N. & Snaith, H. J. “Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites”. Science 338, 643 (2012). [2] Burschka, J. et al. “Sequential deposition as a route to high-performance perovskitesensitized solar cells”. Nature 499, 316-319 (2013). [3] Jeon, N. J. et al. “Solvent engineering for high-performance inorganic–organic hybrid perovskite solar cells”. Nat. Mater. 13, 897-903 (2014). [4] Nie, W. et al, “High-efficiency solution-processed perovskite solar cells with millimeterscale grains”. Science 347, 522 (2015). [5] Nie, W. et al, “Light-activated photocurrent degradation and self-healing in perovskite solar cells”, Nat. Comm. 7, 11574 (2016). [6] Tsai, H. et al,” Effect of Precursor Solution Aging on the Crystallinity and Photovoltaic Performance of Perovskite Solar Cells” Adv. Ener. Mat. 7, 1602159 (2017) [7] Nie, W. et al, Adv. Mater. (In press)