Crystallinity and grain boundary control of TIPS-pentacene in organic thin-film transistors for the ultra-high sensitive detection of NO₂

Herein, ultra-sensitive nitrogen dioxide (NO₂) gas sensors based on 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-pentacene) organic thin-film transistors (OTFTs) are reported. These sensors were fabricated by a simple solvent selection method that enabled crystallinity and grain boundary (GB) control and regulation; superior sensitivity of the sensors could be achieved using appropriate organic solvents to balance the crystallinity and density of the GBs in TIPS-pentacene films. o-Xylene was proved to be the best organic solvent for the optimization of the crystallinity and GB density in TIPS-pentacene films. The sensitivity of the sensors processed using o-xylene towards 10 ppm NO₂ was more than 58 times that of the devices processed using the chlorobenzene solvent. Importantly, the limit of detection (LOD) of 1.93 ppb was achieved by our best NO₂ sensors. A series of characterizations and tests, including morphology, crystal structure, and surface chemical group measurements, were carried out to illustrate the sensing mechanism. Moreover, the real-time sensing, reproducibility, selectivity, and low gate-voltage tests of these devices were conducted, and the results demonstrated that the selection of an appropriate solvent was essential to achieve high-performance gas sensors.