Humidity response of phthalocyanine gas sensors

The sensitivity of CoPc and CuPc thin-film gas sensors to water vapour has been investigated as a function of relative humidity in air, nitrogen and oxygen. Qualitatively similar behaviour was observed for these two phthalocyanines. Water behaves as a donor impurity and there is evidence from both desorption data and Arrhenius plots of the dark conductivity that two types of adsorption or bonding are involved. The significant response of these two materials to humidity indicates that the role of water vapour must be given consideration in studies of the viability of phthalocyanines for detection of toxic gases such as NO₂ and NH₃.