Understanding the underlying physics of charge transport in organic semiconductors under different conditions is important for the development of applications exploiting their properties. The aim of this project is to investigate the effects of illumination on a bottom-gate bottom-contact diF-TES ADT thin-film transistor with visible light of different wavelengths and intensities. When the channel of the transistor was illuminated with visible light the output current increased due to exciton

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... eation and dissociation and the transfer curves shifted to positive values, which was correlated with the absorption spectrum of the organic semiconductor. The number of photo-induced carriers measured was greater than what exciton generation alone could provide (η > 1). Two independent models of photogeneration from blocking contacts were devised to explain the observed phenomena. Photoresponsivities larger than 600 mA/W were achieved for λ < 575 nm, which exceeds the majority of organic and silicon photodetectors. The bias stress effect and device recovery were also studied by observing the shift of the transfer characteristic and the current change over long periods of time. Finally, the dependence of the electrical parameters of an organic transistor on the relative humidity was investigated. Device performance deteriorated under stress and at higher levels of moisture.