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Now organic thin film transistor technology gains growing maturity, high performance organic photodetectors are the missing link towards full organic photosensitive sensor arrays, needed for the realization of applications like organic scanners and organic cameras. In the borderline of the research in organic solar cells, research in organic photodetectors has mainly been limited to organic photodiodes. However, phototransistors offer the possibility to reach higher sensitivities, thanks to the internal current gain of a transistor structure. This document focuses on organic field-effect phototransistors (organic photoFETs) where illumination can be used as an optical gate signal in addition to the electrical gate signal. An experimental description of pentacene photoFETs during broadband illumination is given. A distinction between the direct photocurrent and the additional current enhancement by a thresholdshift can be made, and a relation for this thresholdshift in function of time is revealed. Consequently, the difficulty to compare different organic photoFETs without any information about the illumination time is highlighted and a comparison based on this power law is proposed. Subsequently it is pointed out that by the stability of this thresholdshift after illumination, the pentacene photoFET does not only act as a light detector but also as a memory element, capable to store information about illumination power and duration for an extended amount of time.

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