Effective performance improvement based on dioctylbenzothienobenzothiophene/pentacene isotype organic heterojunction transistors

Organic thin film transistors (OTFTs) with isotype heterojunction semiconducting layers composed of p-type pentacene and dioctylbenzothienobenzothiophene (C8BTBT) have been fabricated. In our heterojunction OTFTs, continuous pentacene film is deposited on top of C8BTBT as a secondary semiconducting layer, which not only can play the role of interfacial layer for hole carriers injection from copper (Cu) source/drain (S/D) electrodes to C8BTBT but also provide another hole transport channel itself. The device performance is then effectively improved. According to the careful study of the C8BTBT/pentacene heterojunction from the film morphologies, it is found that the C8BTBT film facilitates the growth of the upper pentacene film which can further contribute to performance enhancement of the OTFTs. Moreover, diode characteristics with the C8BTBT/pentacene heterojunction show a negligible heterojunction effect that makes the off-state current of OTFTs easy to control. The resulting OTFT exhibits high performance with a mobility of 1.5 cm2/Vs and an on/off ratio of 105, even with low work function Cu S/D electrodes.