Unnatural Hygroscopic Property of Nicotinic Acid by Restructuring Molecular Density: Self-Healing Halide Perovskites.

An unnatural hygroscopic property of nonhygroscopic nicotinic acid (NA) is demonstrated by tuning the intermolecular distance. After addition of NA into methylammonium lead iodide, (MAPbI3) NA molecules are preferentially aligned on the interface of the three-dimensional (3D) MAPbI3 crystal structure by a hydrogen bond. This unique behavior allows NA to be used as a versatile additive to improve the water durability of MAPbI3. After exposure under a high humidity atmosphere (RH 100%, 35 °C), MAPbI3 films with NA exhibited self-healing phenomena against moisture while bare MAPbI3 rapidly lost its own intrinsic property. Density functional theory (DFT) calculations were conducted to reveal how H2O molecules can effectively be absorbed by NA according to its planar molecular density. Also, further optimization of photovoltaic device performances was carried out by investigating the relationship between NA concentration and additive alignment.