Nanostructure-assisted solvent vapor annealing of conjugated polymer thin films for enhanced performance in volatile organic compound sensing

Controlling both the charge transport properties and morphologies of conjugated polymer (CP) films is critical for the practical use of CP-based organic field-effect transistor (OFET) sensors in diverse applications. Herein, we report a facile processing strategy for improving the sensing performance of OFET-based volatile organic compound (VOC) sensors, which significantly enhances charge transport and increases the surface-to-volume ratio of conjugated polymer thin films using solvent vapor annealing (SVA) in the presence of pre-formed nanostructures (PNs) on the films. In this study, two different PN-embedded poly(3-hexylthiophene) (P3HT) films, viz. PN1-P3HT and PN2-P3HT, were obtained from a sonication-treated P3HT solution with nanocrystals (NCs) and nanorods (NRs) and UV-light-irradiated P3HT solution with NCs and nanowires (NWs), respectively. The effect of SVA on the morphologies and charge transport of the PN-embedded P3HT films was systematically studied by atomic force microscopy, polarized optical microscopy, X-ray diffraction analysis, and charge-carrier mobility measurements. Gas sensing measurements were performed by exposing the sensors to VOCs in a concentration range of 1–100 ppm. After SVA, longer, one-dimensional P3HT nanostructures were formed in the PN-embedded films, while some small nanostructures appeared in the pristine P3HT films. Consequently, the PN2-P3HT OFETs exhibited a significant enhancement (2-fold) in charge transport and an increase (1.7-fold) in the surface-to-volume ratio after the SVA. Furthermore, the OFET sensors exhibited excellent responsivities (20–70%) and rapid response/recovery times (110–160 s) in the detection of VOCs.