| Project Detail |
Electronic devices based on semiconductor technology are part of our everyday lives. Organic pi-conjugated semiconductors are an attractive alternative to their widely commercialized inorganic counterparts. They are favoured by tuneable optoelectronic properties, excellent mechanical characteristics (lightweight, flexibility) and low-cost processability to solid-state films. Applications include organic field effect transistors (OFETs), light-emitting diodes (OLEDs), photovoltaics (OPVs) and bioelectronic devices such as electrochemical transistors (OECTs). However, their implementation suffers from the low conductivity of organic semiconductors, which originates from their intrinsically low charge carrier density and mobility. Fundamentally understanding how additional conductive charges are generated and how to enhance their mobility is therefore primordial for the advancement of the field. In the proposed project, my team will use spectroscopic expertise to investigate charge transfer (CT) reactions that add extra positive or negative charge to the conjugated backbone, a process commonly known as doping. Doping either involves CT with a dopant molecule in the ground state (chemical doping) or in the excited state (photo-induced doping), or CT with an electrode (electrochemical doping). The generated charges are not necessarily conductive, since their mobility can be hampered by an unfavourable electronic structure (localized orbitals, low transfer integrals), by energetic or structural disorder (possibly enhanced in the presence of the dopant) and by Coulomb trapping with the dopant or electrochemical counterions. To elucidate those effects, it is essential to consider the transport properties over various length scales, since charge mobility in disordered organic semiconductors depends on distance. We will gain unique insights to the local conductivity probed at the nanometre scale using highly sensitive terahertz (THz) spectroscopy developed in my group. This will be compared to the conductivity in macroscopic devices. Moreover, to understand and overcome the mobility limitations, we will not only investigate conventional conjugated polymers, but we will also explore innovative organic materials where the structure, delocalization, porosity and dimensionality can be controlled: Aligned polymer chains, two-dimensional (2D) polymers and 2D-covalent organic frameworks (COFs). We will provide the comprehensive and generalized understanding necessary to unlock the full potential of such carbon-based semiconductors. This will foster the targeted design of electronic, thermoelectric, photovoltaic and bioelectronic applications to meet Society’s needs for sustainable energy and biomedical materials. |
