ИСТИНА

In the ambipolar organic field-effect transistors a spatially localized photoelectric effect can take place (Fig. 1a). The electron-hole recombination zone in channel of such transistors can act as a photosensitive region where the maximum electric field is reached so that the photogenerated electron-hole pairs are efficiently separated. The position of the 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 in ambipolar organic field-effect transistors [1]. The possibility of controlling the recombination zone spatial position is promising for development of new devices, such as optical image scanners with high spatial resolution [2]. 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 on VG [3]. Fig. 1. Organic phototransistor scheme (a), dependences of the normalized photocurrent Jph/Jdark (solid lines, scale on the left), the parameter ΔWR characterizing the spatial resolution (dashed lines, scale on the right) and response time (dots, scale on the right) for stepwise (tanh) and exponential (exp) forms of P(E) (shown on inset) on the parameter E0, which characterizes the P(E) forms (b). Phototransistor performance with spatially localized photoelectric effect largely depends on the form of the e/h-pair dissociation probability P dependence on the electric field E; two different forms of such P(E) dependences were studied: stepwise (tanh) and exponential (exp, Fig. 1b). Stepwise form of P(E) turns out to be optimal for obtaining a high spatial resolution and normalized photocurrent. The exponential form of the field dependence can provide high photocurrent values at moderate spatial resolution and response times. The results obtained in this work can contribute to the development of new organic semiconductor materials for novel optoelectronic devices. This work was supported by RSF (project № 22-79-10122). [1] M. Kemerink, D. S. H. Charrier, E. C. P. Smits, S. G. J. Mathijssen, D. M. de Leeuw, R. A. J. Janssen, Appl. Phys. Lett. 2008, 93, 033312/1-3 [2] V. A. Trukhanov, JETP Lett. 2019, 109, 776-780 [3] V. A. Trukhanov, Moscow Univ. Phys. Bull. 2020, 75, 342-353