Surface engineering of zinc phthalocyanine organic thin-film transistors results in part-per-billion sensitivity towards cannabinoid vapor

Phthalocyanine-based organic thin-film transistors (OTFTs) have been demonstrated as sensors for a range of analytes, including cannabinoids, in both liquid and gas phases. Detection of the primary cannabinoids, Δ 9 -tetrahydrocannabinol (THC) and cannabidiol (CBD), is necessary for quality control and regulation, however, current techniques are often not readily available for consumers, industry, and law-enforcement. The OTFT characteristics, X-ray diffraction (XRD) spectra, and grazing incident wide angle x-ray scattering (GIWAXS) spectra of two copper and three zinc phthalocyanines, with varying degrees of peripheral fluorination, were screened to determine sensitivity to THC vapor. Unsubstituted ZnPc was found to be the most sensitive material and, by tuning thin-film morphology, crystal polymorphs, and thickness through altered physical vapor deposition conditions, we increased the sensitivity to THC by 100x. Here we demonstrate that deposition conditions, and the resulting physical film characteristics, play a significant role in device sensitization. Organic thin film transistors are potent sensors, but their charge transport layers (CTL) need to be carefully designed to reach desired analyte responses. Here, the authors show that zinc phthalocyanine sensors with a CTL thickness of 200 Å and low crystallinity are most susceptible to physical alterations upon exposure to analytes, resulting in large electrical changes and a low detection limit of 40 ppb for Δ9-tetrahydrocannbinol vapor.