Organic Electronic Device Based On Diketopyrrolopyrrole Donor-acceptor Conjugated Polymer

Donor-acceptor (D-A) conjugated semiconducting polymers are one of important functional polymer materials being studied. Narrow-bandgap polymers with alternative D-A structure have been obtained. Optical and electronic properties of organic semiconductor can be optimized by molecular design through adjusting electron-rich or electron-poor units, facilitated by intramolecular charge transfer. D-A conjugated polymers have been promising for various applications including organic photovoltaic cells, organic light-emitting diodes and organic field-effect transistors (OFET).Electrical properties of conjugated polymers are fundamentals of practical applications. The work in this thesis presented a comprehensive investigation on the electrical performance of a new diketopyrrolopyrrole-based polymer, poly[divinyl-bis(hexyloxy)benzene-alt-diketopyrrolopyrrole] (C6-PPV-DPP), with OFET configuration. The result indicated that this polymer is p-type material. The influence of gate bias on the contact resistance and hole mobility was investigated. The mobility increases with the increasing gate bias, after removing the contact effect. The factors, such as surface morphology, film aggregation and annealing treatment, which affect device performance, are investigated and discussed. It's found that the transistor performance can be enhanced by thermal treatment due to improved localized crystallization of polymer film.Recently, the research on negative differential resistance behaviors (NDR) in organic semiconductors has been made rapid progress. NDR devices can be used for amplifiers, oscillators and low power memories. In this work, a voltage-controlled reproducible and stable NDR behavior was observed in single-layer polymer devices based on C6-PPV-DPP. The NDR characteristics of these devices were thoroughly investigated from different aspects of fabrication and measurement, including film thickness, bias scanning rates, air exposure time and thermal treatments. NDR effect appears only in ultrathin thin films with the thickness ranged between several tens of nanometers and one hundred nanometers. This phenomenon was explained by a model based on filamentary conduction disturbed by dipoles in view of experimental results.