Comparison of semiconductor growth and charge transport on hydrophobic polymer dielectrics of organic field-effect transistors: Cytop vs. polystyrene

Organic field-effect transistors (OFETs) have been fabricated by deposition of an organic semiconductor on inorganic dielectric layers like SiO2. However, inorganic oxide dielectrics have hydrophilic surface properties, which interrupts the growth of organic semiconductors with highly aligned and π-extended domains, and provide many absorbing sites for moisture that work as trap sites for charge carriers. To overcome this problem, a proper surface-treatment method is required to improve the morphology of organic semiconductors. In this study, we treat SiO2 dielectrics with polystyrene (PS) and Cytop (a fluorinated cross-linkable polymer) to tune the surface properties when fabricating pentacene-based bottom-gate top-contact OFETs, and analyzed the influence of surface functionalization on the growth of the pentacene crystals under different deposition conditions and electrical device characteristics. By comparing the morphological features of pentacene with the device characteristics, the effect of hydrophobicity on the morphology of the pentacene polymorph, strongly related to the charge-transport mechanism, could be described.