Despite the growing interest in halide
perovskite-based NH3 sensors, the NH3 sensing
mechanism is still not
well understood. Here, we report an anomalous behavior of resistance
enhancement in CH3NH3PbI3(MAPbI3) perovskite films upon exposure to NH3 gas, which
is contrary to a resistance drop trend in previously reported perovskites.
We propose a NH3 sensing mechanism in which the anomalous
resistance enhancement is dominated by grain boundaries of perovskites.
It is demonstrated that NH3 molecules can substitute MA+ cations of MAPbI3 to form the insulating NH4PbI3·MA intermediate layers onto the surface
of crystal grains, thereby resulting in an increase of resistance.
Additionally, we construct the MAPbI3-based sensor, and
achieve a gas response of 472% toward 30 ppm of NH3. This
study suggests the potential of the perovskite-based NH3 sensors, and also provides guidance for developing high-performance
sensing perovskite materials.
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