Solution-processed Passivation Layer for Air Stability of Organic Thin Film Transistors

Abstract

Organic Thin Film Transistor exposed to air is known to have short lifetime. Therefore, passivation layer is required to prevent air, water vapor from penetrating to OTFT. In this study, hydrophobic materials which are applied in order to prevent water from penetrating to OTFT is deposited on Poly(9,9-dioctylfluorene-co-bithiophene) (F8T2), as solution-processable liquid crystalline polymer, based Organic Thin Film Transistors (OTFTs). Polydimethylsiloxane(PDMS) and Poly[4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole]-co-tetrafluoroethylene are used as passivation layers. The device with PDMS has longer lifetime than without PDMS. However, the device with PDMS/Teflon has longer lifetime than with PDMS. Because PDMS/Teflon passivation layer has high hydrophobicity, solubility of water in passivation layer is low and water is hard to penetrate into passivation layer. As a result, the lifetime of F8T2 OTFT with PDMS/Teflon is 4300 hour, which is comparable with that of F8T2 OTFT with PDMS(3000 hour), without passivation (1700 hour).