Photoresponsive ambipolar transport characteristics of organic thin film transistors using soluble HB-ant-THT and PCBM composites

We report on the photoresponsive ambipolar transport characteristics of organic thin film transistors (OTFTs) with two different types of electrodes using composites of soluble p-type x-shaped small molecules, 5,5′-(9,10-bis((4-hexylphenyl)ethynyl) anthracene-2,6-diyl)bis(ethyne-2,1-diyl)bis(2-hexylthiophene) (HB-ant-THT) and n-type molecules, (6,6)-phenyl-C61-butyric acid methyl ester (PCBM). Composites of HB-ant-THT and PCBM with varying concentration ratios were spin-coated as an active layer and thermal annealing was performed to increase the crystallinity of the active layer. The ambipolar transport characteristics were observed by applying the gate bias in OTFTs with a Au–Au electrode. With increasing the concentration of n-type PCBM, the hole mobility decreased while the electron mobility increased. We observed that the photocurrent in the OTFTs increased upon light irradiation. Ambipolar OTFTs prepared with Au–Al electrodes showed weak photovoltaic effect, and the power conversion efficiency of the devices increased with increasing the PCBM concentration.