Air-Stable Spin-Coated Naphthalocyanine Transistors for Enhanced Chemical Vapor Detection

Air-stable organic thin-film transistor (OTFT) sensors fabricated using spin-cast films of 5,9,14,18,23,27,32,36-octabutoxy-2,3-naphthalocyanine (OBNc) demonstrated improved chemical vapor sensitivity and selectivity relative to vacuum-deposited phthalocyanine (H2Pc) OTFTs. UV–vis spectroscopy data show that annealed spin-cast OBNc films exhibit a red-shift in the OBNc Q-band λmax which is generally diagnostic of improved π-orbital overlap in phthalocyanine ring systems. Annealed OBNc OTFTs have mobilities of 0.06 cm2 V–1 s–1, low threshold voltages (|Vth| 6. These air-stable device parameters are utilized for sensing modalities which enhance the sensitivity and selectivity of OBNc OTFTs relative to H2Pc OTFTs. While both sensors exhibit mobility decreases for all analytes, only OBNc OTFTs exhibit Vth changes for highly polar/nonpolar analytes. The observed mobility decreases for both sensors are consistent with electron donation trends via hydrogen bonding by basic analytes. In contrast, Vth changes for OBNc sensors appear to correlate with the analyte’s octanol–water partition coefficient, consistent with polar molecules stabilizing charge in the organic semiconductor film. The analyte induced Vth changes for OBNc OTFTs can be employed to develop selective multiparameter sensors which can sense analyte stabilized fixed charge in the film.