Fabrication of 1-D organic semiconductor nanomaterials and their optoelectronic applications

Abstract

There are many kinds of one-dimensional (1-D) nanomaterials such as nanofiber, nanoribbon, nanotube and nanowire. They have been widely studied over a decades because they are promising materials for applications in various optoelectronic devices such as organic photovoltaic cell, flexible sensor, phototransistor, organic light-emitting diode. Recently, on the other hand, 1-D nanomaterials with unique structure morphologies have been developed and applied to optoelectronic devices that can exhibit unusual electrical characteristics, and these unconventional 1-D nanomaterials were employed for fundamental study in organic electronics. In this work, 1-D organic semiconductor nanomaterials with unconventional structures including branched nanowires have been developed and used for various optoelectronic devices. In addition, the fundamental charge transport mechanisms have been investigated. First, we synthesized branched wires by modifying the morphology of 1-D nanowires from solution phase. The injection of different kinds of non-solvents, such as methanol, ortho-dichlorobenzene or a nanowire-dispersed solution, greatly affected the growth mechanism of nanowires during the π- π stacking of molecules and resulted in the formation of branched wires. Organic field-effect transistors (OFETs) were fabricated for the fundamental study on the charge transport of these branched nanowires. Electrical characterizations of over one hundred samples and investigation of activation energy by temperature analysis suggests that there is difference in the electron mobility of branched wires upon switching the source-drain direction. For second experiment, a highly photo-sensitive material (2Z,2'Z)-3,3'-(2,5-dimethoxy-1,4-phenylene)bis(2-(3,5-bis(trifluoromethyl)phenyl)acrylonitrile) (DM-R) and other three materials were synthesized with high purity. These materials were easily fabricated into nanowires by stacking π-π self-assembly in solution-phase. By using these nanowires, highly photo-sensitive field-effect transistor was fabricated and their photo-responsivity was measured in high-vacuum condition to compare with their thin film structure. For third experiment, nanoparticle-embedded magnetically-alignable nanowires were synthesized via the injection of iron oxide nanoparticle dispersed ethanol as a non-solvent in a hot BPE-PTCDI solution. The nanowire was aligned by external magnetic force due to the embedded magnetic nanoparticles inside the body of nanowire. For the application to the memory, the field-effect transistor device was fabricated and its memory characteristics were measured.