High Speed Ultraviolet Phototransistors Based on an Ambipolar Fullerene Derivative

Combining high charge carrier mobility with ambipolar transport in light-absorbing organic semiconductors is highly desirable as it leads to enhanced charge photogeneration, and hence improved performance, in various optoelectronic devices including solar cells and photodetectors. Here we report the development of [6,6]-phenyl-C<sub>61</sub>-butyric acid methyl ester (PC<sub>61</sub>BM)-based ultraviolet (UV) phototransistors with balanced electron and hole transport characteristics. The latter is achieved by fine-tuning the source–drain electrode work function using a self-assembled monolayer. Opto/electrical characterization of as-prepared ambipolar PC<sub>61</sub>BM phototransistors reveals promising photoresponse, particularly in the UV-A region (315–400 nm), with a maximum photosensitivity and responsivity of 9 × 10<sup>3</sup> and 3 × 10<sup>3</sup> A/W, respectively. Finally, the temporal response of the PC<sub>61</sub>BM phototransistors is found to be high despite the long channel length (10 s of μm) with typical switching times of <2 ms.