Air-stable and balanced split-gate organic transistors

Ambipolar organic electronics have been gaining interest as a simple alternative technology for implementing complementary-like circuits. Although practical applications require stable operation in the air, most previous studies on ambipolar organic electronics have reported results measured in high vacuum or N₂ atmosphere only. This is because ambipolar properties change to asymmetric p-type dominant or unipolar p-type characteristics when exposed to air. Little effort has been put into the fundamental investigation of the effects of the environmental atmosphere on ambipolar organic semiconductors. In this paper, we demonstrate ambipolar OTFTs with balanced p/n characteristics under ambient air using poly{[N,N′-bis(3-decylpentadecyl)-naphtho[2,3-b:6,7-b′]dithiophene-4,5,9,10-tetracarboxidiimide-2,7-diyl]-alt-5,5′-(2,2′-bithiophene)} (PNDTI-BT-DP). Based on the analysis using XPS, UPS, and electrical characterizations at various atmosphere, we concluded that the PNDTI-BT-DP has 0.45 eV higher than the target value for ambiplar charge injections with respect to Au contact electrode. The energy level of the PNDTI-BT-DP was up-shifted by 0.45 eV when the film was exposed to ambient air, which resulted in a change in the electrical properties. As a proof-of-concept application, we demonstrate the air-stable split-gate OTFTs that operate as either a unipolar p- or n-type device based on electrical control. Finally, we report results showing that the device characteristics for both p- or n-type operations were maintained after ∼120 h of atmospheric exposure.