Semi-transparent and flexible organic transistors using PEDOT: PSS gate and Parylene-C gate dielectric and their optical sensor application

The essential characteristics of organic thin-film transistors (OTFTs) applicable to flexible displays and biosensors are flexibility and biocompatibility. Additionally, by achieving transparency, it is possible to fabricate transparent electronic devices that are visually more natural and interact effectively with their surroundings compared to conventional devices. In this study, we developed a semi-transparent OTFT that satisfies these requirements by utilizing the polymers Parylene-C, PDPP2T-TT-OD(DPP-DTT), and Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)(PEDOT: PSS). Parylene-C was used as the substrate and gate insulator, ensuring the transparency and flexibility of the OTFT. PEDOT: PSS, employed as the gate electrode, exhibited ease of processing, high flexibility, and a transparency of 92%. Additionally, DPP-DTT, used as the channel material, is a p-type polymer that allows for thin-film formation through solution processing and spin-coating, thus simplifying the fabrication process. The fabricated semi-transparent flexible OTFT exhibited a mobility of 0.002 cm²/Vs and an I_ON/I_OFF ratio exceeding 10⁵. Finally, by demonstrating that the current in the DPP-DTT channel formed on the transparent gate electrode and insulator changes with light intensity, we confirmed the potential applicability of the proposed semi-transparent transistor as a photosensor.