Unraveling the Ammonia Sensing Behavior and Degradation Pathways of Novel Lead-Free MA2CuBr4 based Ammonia Sensor

We report a lead-free copper-based halide perovskite gas sensor to detect ammonia gas at ambient temperature. The sensor uses methylammonium copper bromide as the active material and can trace ammonia by both visual color change method as well as electrical readout. The maximum calibrated sensitivity based on the optical response of the sensor is ∼95% on exposure to 10 ppm ammonia gas, which is the best among the colorimetric sensors using halide perovskites. The sensor can be operated at 0.5 V bias with an output current of ∼12 μA at 50 ppm ammonia gas exposure, making our device compatible with low-power gas sensors. Also, we studied the degradation mechanism by subjecting the MA2CuBr4 film over ammonia exposure cycles. We found that there are two factors responsible for the degradation of the sensor: (i) loss of methylamine gas due to formation of NH4Br, and (ii) reduction of Cu2+ to Cu+. Increasing the proportion of MABr in the system, increases the material’s tolerance to ammonia exposure by solving the methylamine gas escape problem. Further we have shown that the stability of the device can be enhanced by depositing porous polymethylmethacrylate over the copper perovskite.