ИСТИНА

Organic field-effect transistors (OFET) can combine photodetection and light amplification, i.e. work as phototransistors. Such organic phototransistors can be used in light-controlled switches and amplifiers, detection circuits, and sensors of ultrasensitive images [1]. The main components of the OFET structure are shown in Fig 1a. In this work, we propose a simple one-dimensional numerical model of photosensitive OFET. The model is based on the Poisson, current continuity and drift-diffusion equations with one spatial coordinate directed in plane of the active layer from source to drain electrode. The model allows calculation the dependences of the source-drain current on the source-drain voltage Vd (output characteristics) and on the gate voltage Vg (transfer characteristics). Fig. 1b shows the photocurrent versus Vg (difference between calculated transfer characteristics upon light and in dark) for OFET with p-channel when the Fermi levels of the source and drain electrodes aligned to the highest occupied molecular orbital of the organic semiconductor. As shown in Fig. 1b, there is an optimal value of Vg near 2 V at which the photocurrent is maximal. We figured out that these Vg-dependences of the photocurrent result from variation in the area of efficient charge photogeneration. At Vg<0, the photogeneration of electron-hole pairs is compensated by their recombination in the whole active layer; therefore, the photocurrent tends to zero. At optimal Vg near 2 V, the hole-depleted area is formed near the drain electrode, where the electric field is enhanced and charge recombination suppressed. At higher Vg this area narrows, and Jph decreases. The model shows that the photosensitivity (photocurrent to dark current ratio) at optimal Vg is higher than 10^10. We have studied effects of different OFET parameters such as band gap, charge mobility, channel length, etc. on the photocurrent. We compare the results of modeling with the experimental data. This work was supported by RFBR (project № 15-53-10070). 1. Lucas B., Trigaud T., Videlot-Ackermann C. Polym.Int. 2012, 61, 374-389.