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

Composition-Dependent Optoelectronic Properties of Mixed 2D/3D Metal Halide Perovskite Films for Light-Emitting Diodes

Low-dimensional perovskites with large organic cations have shown great potential for boosting the luminescence efficiency of metal halide perovskite light-emitting diodes (PeLEDs). Although numerous successful results have been obtained for mixed two-dimensional (2D)/three-dimensional (3D) perovskite films, the correlation of the optoelectronic properties with the crystallographic properties and film composition remains elusive. Herein, we investigated the optoelectronic quality of thin films and their impact on luminescence and transport behaviors in a mixed 2D/3D perovskite system containing 2D butylammonium lead bromide (BA2PbBr4) and 3D formamidinium lead bromide (FAPbBr3). Ultrafast transient absorption and temperature-dependent photoluminescence measurements revealed distinct changes in nonemissive decay of the excited states, including the vibrational coupling properties. These behaviors could then be closely correlated with the crystallographic evolution of the perovskite films. We rationalized the performance of PeLED devices and determined the possible limitations to further utilize the advantageous properties of mixed 2D/3D perovskite systems by examining both the luminescence and electrical properties of the perovskite films