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 diffculty 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.
We have realized a light-emitting organic field-effect transistor (LEOFET). Excitons are generated at the interface
of an n-type and a p-type organic semiconductor heterostructure inside the transistor channel. The dimensions
and the position of the p-n heterostructure are defined by photolithography. The recombination region is several
microns from the metal electrodes. Therefore, the exciton quenching probability in this device is reduced.
Numerical simulations show that the recombination region can move within the transistor channel by changing
the biasing conditions.