Asymmetric dithieno[3,2-b:2′,3′-d]thiophene derivatives as solution-processable small molecular organic semiconductors for organic thin film transistors

Abstract

In this paper, solution-processable asymmetric dithieno[3,2-d:2′,3′-d]thiophene (DTT) compounds, 2-octyldithieno[3,2-b:2′,3′-d]thiophene (1), 2-octyl-6-(thiophen-2-yl)dithieno[3,2-b:2′,3′-d]thiophene (2), 2-octyl-6-(5-octylthiophen-2-yl)dithieno[3,2-b:2′,3′-d]thiophene (3), and 2-(5-(2-ethylhexyl)thiophen-2-yl)-6-octyldithieno[3,2-b:2′,3′-d]thiophene (4) were synthesized and employed as small molecular organic semiconductors for top-contact/bottom-gate organic thin-film transistors. Physicochemical properties of four compounds including decomposition temperature, melting temperature, maximum absorption wavelength, highest occupied molecular orbital / lowest occupied molecular orbital energy level, and band gap were investigated. All DTT compounds exhibited p-channel activity, and especially compound 2 with additional thiophene group and linear alkyl chain (octyl group) showed superior electrical performance with hole mobility up to 0.07 cm2/Vs and current on/off ratio > 108 in ambient environment. Moreover, film microstructure and morphology showed correlation with the corresponding electrical performance, where high film texture and terrace-like morphology afforded high device performance.