Benzothienobenzothiophene-Based Conjugated Oligomers As Semiconductors For Organic Thin-film Transistors

According to Marcus theory, the rate of charge transport in organic semiconductors(OCSs) mostly depends on transfer integral and reorganization energy. Extent the lengthof-conjugated system is an effective way to reduce reorganization energy and enhancetransfer integral for small molecule semiconductors lead to higher charge transportmobility. For instance, from anthracene to pentacence, the charge mobility enhanced asthe-conjugated system extended, but the HOMO level get higher as consequence,which result in a poor ambient stabibily for pentacence. Incorporation of heteroatomsuch as N and S into acene can lower HOMO energy level and thus improve theirambient stability. As a member of DAcTT, the alkylatedbenzothieno[3,2-b]benzothiophene(BTBT) derivatives showed good performance bothin charge tarnsport and stability. But the lower HOMO level of BTBT (5.88eV), resultin a large threshold voltage, hinder their commerce application. And the widely value ofcharge transport due to the inhomogeneous of the organic semiconductor film also be ahandicap. Hererine, we focused on BTBT, took a series of research. Main contributionsinclude:1. Two benzothienobenzothiophene (BTBT)-based conjugated oligomers, i.e.,2,2′-bi[1]benzothieno[3,2-b][1]benzothiophene (1) and5,5′-bis([1]benzothieno[3,2-b][1]benzothiophen-2-yl)-2,2′-bithiophene (2), were preparedand characterized. Organic thin film transistors with top-contact and bottom-gategeometry based on1exhibited mobilities up to2.12cm2V-1s-1in an ambientatmosphere.1-based devices exhibited great air and thermal stabilities, as evidenced bythe slight performance degradation after2months of storage under ambient conditionsand after thermal annealing at temperatures below250°C.2. Two star-shape oligomers based on BTBT (8and9) were synthesized andcharacterized. The oligomer8showed liquid crystal properties. Organic thinfilmtransistors based on8throw spin-coating exhibited mobilities to0.027cm2V-1s-1in anambient atmosphere after annealed at80oC.