Organic Thin-Film Transistors Gas Sensor Based on Highly Compact and Ordered Phthalocyanine Semiconducting Nanofilms

The self-assembly ability of metal phthalocyanines derivative (2,9,16,23-tetra-tert-butyl-29H,31H-copper (II)) (CuttbPc) and CuttbPc/stearic acid (SA) monolayers at air-water interface were investigated through the Langmuir-Blodgett (LB) technique. Surface pressure-area per molecule (pi-A) isotherms and Brewster Angle Microscopy (BAM) analysis confirmed that stable CuttbPc/SA monolayer was formed in a titled arrangement at the air-water interface with the assistant spreading of SA surfactant. The ordered molecular arrangement in the complex CuttbPc/SA LB films was examined by UV-Vis absorption spectra and the films morphological characterization was studied by Atomic Force Microscopy (AFM). Moreover, highly compact and ordered CuttbPc complex nanofilms were transferred onto SiO2 as active layer for organic field-effect transistors (OFETs) through a vertical LB film deposition. The AFM images revealed that continuous LB layers were constructed across the SiO2 layer area after 4 layers LB films deposition, and well coverage of LB films on SiO2 surface was obtained. The field-effect mobility and current-voltage (I-d-V-d) performance of OFETs with CuttbPc complex LB films as active layer were characterized. The results demonstrated that a highly compact and ordered nanofilm structure, which is suitable for carries transportation, resulted in high field-effect mobility of OFETs. As a result, the gas sensor based on OFETs with CuttbPc complex nanofilms as active layer exhibited excellent sensitivity and reproducibility to detect low concentration (< 1 ppm) NO2 gas.