Combination of light-induced effect and gate bias stress in organic phototransistors

In this work, the photoresponse of pentacene-based thin film transistors fabricated with a photocurable polymer insulator was investigated under visible and ultraviolet illumination. A simple model was developed to distinguish a photoconductive and a photovoltaic effect, that is, a direct photocurrent and a current enhancement caused by a threshold voltage shift. The direction of the light-induced threshold translation is affected by measurement conditions (e.g. integration time and voltage range) and is related to the nature of the trap states, specifically those located in the pentacene film near the interface with the polymer. In particular, it was shown that, thanks to this phenomenon, the photosensitivity of the fabricated phototransistors could be modulated by the gate bias applied during illumination.