The low conductive electrodeposited poly(2,5-dimethoxyaniline) as a key material in a double lateral heterojunction, for sub-ppm ammonia sensing in humid atmosphere.

We present a new device called double lateral heterojunction (DLH) as ammonia sensor in humid atmosphere. It combines polyani-line derivatives in their poor conducting state with a highly conductive molecular material, lutetium bisphthalocyanine, LuPc2. The polyaniline and poly(2,5-dimethoxyaniline) are electrodeposited on ITO interdigitated electrodes, leading to an original device that can be obtained only by electrochemistry and not by other solution processing techniques. Both polymers lead to highly con-ducting materials that require a neutralization step before their covering by LuPc2. While the device based on polyaniline shows an ohmic behavior, the non-linear I-V characteristics of poly(2,5-dimethoxyaniline) - based DLH proves the existence of energy barri-ers at the interfaces, as demonstrated by impedance spectroscopy. It exhibits a particularly interesting sensitivity to ammonia, at room temperature and in a broad relative humidity range. Thanks to its higher energy barriers, the poly(2,5-dimethoxyaniline)/LuPc2 DLH is the most sensitive device with a limit of detection of 320 ppb. This work paves the way for the use of substituted polyanilines in conductometric sensors not only in the field of air quality monitoring but also in the field of health diagnosis by measurement in human breath.