With record power conversion efficiencies of hybrid perovskite solar cells now exceeding 20% under laboratory conditions, improvements in stability of the cells under real-world working conditions are now key requirements for their commercial success. Here, we present a novel strategy to reduce penetration of humidity and oxygen into perovskite films via incorporation of a diammonium glycol. The two ammonium groups of this molecule allow it to serve as a crosslinker in the structure, bridging two unit cells within a crystallite or even across a grain boundary. In a planar heterojunction solar cell containing PCBM as an electron transport layer, the power conversion efficiency of the cell with similar to 0.1% diammonium glycol in the absorber layer was 13.96%, slightly exceeding that of the glycol-free device (13.53%). Most importantly, the glycol-free device exhibited the typical growth in hysteresis with performance degradation, but hysteresis remained suppressed in the device doped with diammonium glycol, even as its overall performance deteriorated. Futhermore, the chemical stability of the unpackaged device under continuous AM1.5 G illumination at ambient conditions was substantially improved relative to the glycol-free device. Formation of PbI2 was significantly suppressed, which could minimize release of toxic Pb ions.