We report on the preparation of MAPbBr(3) perovskite films of high electronic quality by applying a methylamine (MA) vapor treatment and mitigating surface defects using the amphiphilic molecular passivator, neopentylammonium chloride (NPACl). We find that post-treatment of MAPbBr(3) with methylamine (MA) vapor effectively smooths the surface of the perovskite, eliminating unwanted corrugations and producing phase-pure pinhole free films. The subsequent coating of MAPbBr(3) with NPACl eliminates deleterious surface states that act as electron-hole recombination centers while enhancing the resilience of the perovskite solar cell (PSC) against heat stress and ambient moisture, with solid state NMR demonstrating their atomic-scale interaction. As a result, we achieve an unprecedented V-oc of 1.65 V which is a record level for mesoporous single junction PSCs together with a power conversion efficiency (PCE) of over 10% in standard AM 1.5 sunlight. The PSC also retains 91.3% of its initial performance after 1100 h of light soaking under full sunlight and at 60 degrees C while maintaining the device at maximum power point. In contrast, the pristine PSC maintained only 34% of its initial efficiency under the same aging conditions.