Abstract
Silk fibroin thin film is utilized as the gate insulating material for pentacene organic thin film transistors (OTFTs) fabricated on plastic substrate. A very high field effect mobility (μFE) value of 23.2 cm2V-1s-1 in the saturation regime and a low operation voltage of -3V for the pentacene OTFT made on a flexible polyethylene terephthalate (PET) plastic substrate with silk fibroin as the gate dielectric. Silk fibroin is an insulating protein, which is coated on PET at room temperature by a low-cost solution process. An inverter with a switching speed of 1 MHz is achieved even for the OTFT with large channel length (50 μm). The high device performance enables OTFTs to outperform amorphous semiconducting oxide TFTs such as a-InGaO3(ZnO)5 (a-IGZO) TFTs. The pentacene OTFTs have immediate and profound implications for flexible electronics operated at high switching frequency and low voltage.The secondary structures of silk fibroin thin films can be tuned by varying the casting temperature. Larger amount of turn is in favor of the formation of orthorhombic phase of pentacene and lower interface trap density, which leads to higher field-effect mobility. The best device characteristics occur at a casting temperature of 303 K, which exhibit a very high field-effect mobility value of 21 cm2V-1s-1 in the saturation regime. The device characteristics degrade with the reduction of turn when casting temperature increases from 303 to 393 K. An abrupt reduction of turn occurs at 433 K, accompanying with the appearance of free C=O group and β-sheet. The corresponding device performance is greatly reduced. We also present pentacene OFETs with the water-insoluble silk fibroin film by a post-treatment with methanol as the gate dielectric. The water-soluble silk fibroin dielectric exhibit high field-effect mobility value (μFE,sat) 25 cm2V-1s-1. The μFE,sat degrade to 8.1 cm2V-1s-1 owing to the formation of β-sheet crystalline structure in the water-insoluble silk fibroin film.