Improving room-temperature ammonia sensing properties of CH3NH3PbI3-based gas sensors via coordination interaction using monoethanolamine ligand

Organic-inorganic hybrid perovskite materials have garnered significant research interest owing to their exceptional crystallographic characteristics and remarkable optoelectronic properties. This study presents a breakthrough in room-temperature ammonia sensing through the rational design of CH₃NH₃PbI₃ (MAPbI₃)-based chemiresistive sensors modified with monoethanolamine (MEA) ligands. By integrating MEA as a coordination agent into the perovskite precursor solution, we achieved controlled crystallization dynamics, yielding compact MAPbI₃ films with unique maple-leaf grain morphology and enhanced humidity resistance. The optimized TiO₂/MEA-MAPbI₃ sensor exhibited a nearly 2.1-fold improvement in response amplitude toward 100 ppm NH₃ compared to unmodified counterparts, alongside exceptional selectivity to NH₃ against interfering gases. Crucially, MEA-derived (PbI₂)-MEA-(MAI) molecular shielding layers at grain boundaries suppressed moisture-induced degradation, enabling stable operation in air environment (∼30 %RH) with less than 22 % response degradation over 29 days. Mechanistic analyses revealed that the sensing behavior originates from reversible cation exchange between methylammonium (MA⁺) and ammonium (NH₄⁺) species at the perovskite surface, corroborated by density functional theory (DFT) calculations showing preferential NH₃ adsorption over other analyte gases.