Enhanced sensing performance of nitrogen dioxide sensor based on organic field-effect transistor with mechanically rubbed pentacene active layer

Organic field-effect transistor (OFET)-based nitrogen dioxide (NO₂) sensors with mechanically rubbed pentacene active layer were fabricated by utilizing polystyrene as the dielectric. Compared with those of the reference device, the sensing properties, including sensitivity and response time, were significantly enhanced in OFETs with the pentacene film rubbed parallel to the source/drain electrodes, while the device with pentacene film rubbed perpendicular to the source/drain electrodes showed sensing properties lower than those of the reference device. Atomic force microscope was used to analyze the morphologies of pentacene film with or without rubbing, and much smaller grains of pentacene were observed after mechanical rubbing. Consequently, more grain boundaries which were beneficial to the diffusion of analytes were formed, and NO₂ diffused to the channel of OFET with parallel rubbed pentacene would modify the hole density more effectively as the charge flow in such device was forced to travel through the rubbed pentacene.