Universal sensing of ammonia gas by family of lead halide perovskites based on paper sensors: Experiment and molecular dynamics

In this paper we show that, high sensitivity and high selectivity room temperature ammonia (NH3) gas sensors with both visual and electrical response can be made from family of lead halide perovskites with different cations and anions. These sensors, based on papers, act as general platforms for new generation of solid state gas sensors for sensitive detection of NH3 gas by simple color change (similar to 10 ppm sensitivity) as well as electrical resistance change with sub ppm sensitivity limited by electrical noise only. The sensors with materials like CH3NH3PbI3 (MAPI), CH3NH3PbBr3 (MAPB) and CH(NH2)(2)PbI3 (FAPI), are grown on paper from solution. MAPB changes color from orange to white and FAPI and MAPI from black to yellow under NH3 gas exposure respectively. For electrical sensor operation, a fixed concentration (20 ppm) of NH3 gas, the sensitivity of MAPI is highest at 96 % followed by MAPB at 82 % and FAPI at 65 %. The sensors with electrical read out could trace NH3 gas well below ppm level with only few nanowatt of power consumption. Based on experiments, a sensing mechanism has been proposed. The proposed mechanism mainly consists of decomposition of the perovskite halides to lead (Pb) halide by preferential adsorption of NH3 gas molecules. The proposed mechanism has also been substantiated by molecular dynamics simulations. These sensors fabricated by simple solution process on paper substrates and operable at ambient temperature, are compatible with very low power (similar to nW) paper electronics