Thermally deposited silk fibroin as the gate dielectric layer in organic thin-film transistors based on conjugated polymer

This study investigated the morphology, structural transformation, and electric properties of organic thin-film transistors (OTFTs) with silk fibroin as their dielectric layer at different annealing temperatures. Silk fibroin was employed because it can simplify the OTFT fabrication process and decrease fabrication cost. We successfully fabricated OTFTs based on poly(3-hexylthiophene) (P3HT) dissolved in chlorobenzene (CB) or 1,2,4-trichlorobeneze (TCB). The P3HT had fiber-like network structures when TCB was used and isolated spherical domains when CB was employed. The nanowire morphology obtained when TCB was used may have enabled efficient charge transport. The silk fibroin layer annealed at 40 °C had the smallest particles and least aggregate. The calculated field-effect mobility was 2.06 × 10−3 cm2 (Vs)−1 (when TCB was used), and the highest on/off ratio was 103, obtained for the silk fibroin annealed at 40 °C. The OTFT with the 40 °C-annealed-layer had the best performance because of the smooth surface of the α-helix structure of this silk fibroin layer, with such smoothness enabling favorable P3HT crystalline formation. Biological materials such as silk protein are low cost and environmentally friendly and require low temperature in manufacturing. This study indicates the suitability of silk fibroin for use in various electronic devices.