Transistor performance of a “push-pull”, π-stacked bithiazole-ethylenedioxythiophene co-oligomer

Abstract

The “push-pull” co-oligomer, 5,5′-bis(4,4′-dibutyl-2,2′-bithiazol-5-yl)-(3,4,3′,4′-bis(ethylenedioxy)-2,2′-dithienyl) (BT₂B) was used to construct organic field effect transistors (OFETs) via vacuum evaporation or by solution casting of BT₂B crystals. Crystalline OFETs made in either top- or bottom-contact configuration had measured field effect mobilities of (3–4) × 10⁻³ cm² V⁻¹ s⁻¹. INDO and EHT molecular orbital calculations show that the HOMO is confined to the central EDOT fragment whereas the LUMO is concentrated on the relatively electron-poor bithiazole rings. This charge confinement, when combined with the molecular offset in the π-stacked crystal structure, leads to relatively small transfer integrals. Even so, the intrinsic hole mobility was computed to be as high as 0.86 cm² V⁻¹ s⁻¹.