Doping of Conjugated Polymers: Preparation, Characterization and Device Fabrication

Semiconducting conjugated polymers (CPs) as emerging materials for advanced electronic applications such as sensors, OPVs, and OEFTs has become an intriguing research topic in the past decades. It opens a new avenue of “flexible” electronics, which has shown great potential in next-generation electronic devices. However, due to the nature of CP materials and related solution processing techniques, unlike almost perfectly crystalline silicon materials, CPs in the solid-state often exhibit much lower crystallinity if it is not complete amorphous, which severely hinder the electronic property and optical property of the materials. The crystallinity of CPs in a film is often uniquely governed by the aggregation process involving intermolecular interactions such as π-π stacking. On the other hand, chemical doping of CPs by a dopant is regarded as an effective method to enhance the performance of CPs by increasing their conductivity by several orders of magnitude. By a combination of optical and microscopic techniques, the π-π aggregation of P3HT, a typical CP, has been proved to capable of promoting its chemical doping with F4TCNQ. The I-V characteristics shows that the doped P3HT film has a 105 times higher conductivity than the undoped P3HT film. Besides the preparation of CP films, novel nanostructures of CPs such as highly crystalline nanowires with a widthtechnique, the relationship between surface potential and doping regime can be established for chemically doped P3HT nanowires. Overly doped P3HT nanowires exhibit distinct “dot-like” dark features in KPFM imaging as compare to undoped and iv moderately doped P3HT nanowires, which is corresponding to the morphological feature in the AFM topography imaging. Apart from chemical doping of CPs, a new doping route based on manipulating ion injection into/out of the CP films has been developed. The so-called organic electrochemical transistors (OECTs) have been fabricated on interdigitated electrodes (IDEs). This lithography-free set-up of OECTs show improved water stability under cycling gate bias conditions after crosslinking, which provides a useful platform for the applications such as bio-sensing