ИСТИНА

Organic field-effect transistors can exhibit a photoelectric effect, i.e. act as phototransistors. Photoelectric effect should be more efficient in ambipolar transistors because both photogenerated electrons and holes can contribute to the photocurrent. In ambipolar transistors, the position of the electron-hole recombination zone in the channel can be controlled by the gate voltage, VG. The typical width of this zone is in the range of 15-200 nm.1 The ability to control the spatial position of the recombination zone can be used for studying the fundamental processes in organic semiconductors2 and also is promising for development of new devices, such as optical image scanners with high spatial resolution.3 In such ambipolar organic field-effect transistor, the recombination zone acts as a photosensitive region where the maximum electric field is achieved so that the photogenerated electron-hole pairs are efficiently separated. Using numerical modeling, it was shown that the normalized photocurrent Jph/Jdark dependences on VG can reproduce the spatial profiles of incident light intensity across the phototransistor channel, after transformation of the VG-scale to x-scale in accordance with the position dependence of the electric field peak, xpeak, on VG Also modelling showed that the response times of such phototransistor can be about several nanoseconds. Further it was shown by numerical modeling that the phototransistor performance with spatially localized photoelectric effect largely depends on the form of the e/h-pair dissociation rate dependence on the electric field; different forms of such dependences were studied. The results of modeling were supported by experimental data: spatially-localized photoelectric effect was observed in ambipolar organic field-effect transistor based on thin film of six-ring thiophene-phenylene co-oligomer with trimethylsilyl end groups.