Modification of C60 nano-interlayers on organic field-effect transistors based on 2,7-diocty[1]benzothieno-[3,2-b]benzothiophene (C8-BTBT)/SiO2

The modification of C 60 nano-interlayers on the organic field-effect transistors (OFETs) based on 2,7-diocty[1]benzothieno-[3,2-b]benzothiophene (C8-BTBT)/SiO 2 was addressed at both the electronic structure and device level. It is observed that a band bending occurs in C8-BTBT layer with the insertion of C 60 , which induces a strong hole accumulation at the interface region, facilitating the formation of high concentration conducting channel when the interface is incorporated into OFETs. The strong acceptor C 60 may cause charge transfer from the trap states in C8-BTBT, resulting in a field-effect operation with decreased threshold voltage. However, the increasing disorder in C8-BTBT induced by the C 60 nano-interlayer may reduce the hole mobility at the C8-BTBT/SiO 2 interface region and change the growth model of C8-BTBT. In addition, as confirmed by the transfer characteristic of the OFETs, the thin C 60 insertion layer isn’t continuous enough to induce an ambipolar transport behavior despite its high mobility. The competition between the two opposite effects results in compromised performance in such OFETs. The device performance parameters deteriorate generally with increasing the C 60 nano-interlayer thickness. So, it is inferred that the C 60 interlayer alone cannot improve the performance of the C8-BTBT/SiO 2 -based OFETs without further optimization. Importantly, the device performance exhibits an abnormal improvement with a 6 nm C 60 interlayer, which might be ascribed to a higher energy level shift of C8-BTBT caused by a quasi-continuous C 60 film at this thickness.