Organic phototransistors based on solution grown, ordered single crystalline arrays of a π-conjugated molecule

Abstract

High quality, single crystalline, ordered arrays of a π-conjugated organic molecule, N,N′-dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C₈), were grown by solution processing and used to fabricate a low-cost, high-performance organic phototransistor (OPT). The single crystalline nature of the microstructure was investigated using 2D-GIXD measurement. The organic field-effect transistor fabricated using periodic arrays of elongated crystals exhibited a photoresponsivity (P) of ca. 1 A W⁻¹ and a photo to dark current ratio (I_on/I_off) of 2.5 × 10³ at V_G = 12 V and a maximum P of ca. 7 A W⁻¹ at the high gate bias regime (V_G = 50 V) with an optical power of ca. 7.5 mW cm⁻². With polymeric gate dielectric, the OPT exhibited very stable n-type characteristics both in the dark and under light illumination and showed reproducible photo-switching behavior. The dependence of the photocurrent on the gate/drain voltage and on illumination intensity provided an effective way to control the number of photo-carriers generated in the active material, enabling the precise tuning of the device's performance. Performance comparison between OPTs with ordered crystal arrays and thin films of PTCDI-C₈ confirmed that the material's intrinsic properties were better realized in the crystalline device, presumably because of higher charge carrier mobility and better charge transport capability. This one-step, solution-based, self-assembly fabrication of multifunctional (photodetection, photoswitching, signal amplification) optoelectronic devices has potential to aid the development of organic semiconductors with high-quality micro/nanostructures for large-scale application and low-cost optoelectronic devices.