Solution processed, aligned arrays of TCNQ micro crystals for low-voltage organic phototransistor

Abstract

A simple approach is developed to prepare periodic arrays of large, elongated crystals of π-conjugated organic molecules, viz, 7, 7, 8, 8-tetracyanoquinodimethane (TCNQ) through a solution based method. The ordered crystalline array is successfully used to fabricate low-voltage organic phototransistors (OPT). The OPT with polymeric gate dielectric exhibits very stable n-type characteristics with a low threshold voltage (<0.5 V). Under illumination, the devices produce a current gain (I_light/I_dark) of 31 at V_G = 0.3 V. Photoswitching occurs within 10 ms and photosensitivity is greater than 1 mA W⁻¹ at low driving voltages and low optical powers. The drain current increases gradually with increasing the illumination intensity resulting in typical output FET characteristics. The one-step, solution-based, self-assembly method for highly ordered organic crystals in large area could have significant potential for future large-scale and low-cost optoelectronic devices. In addition, this study aims to aid the development of organic semiconductor materials with high quality crystalline structures for various optoelectronic applications.