Towards more efficient solar cells: Understanding the relations between structure and electrical conductivity in suspensions of conductive PEDOT

Photovoltaic (PV) technology is regarded as one of the most renewable and economically viable energy sources to address the grand challenges of the energy issue in the near future. In this perspective, organic photovoltaics (OPV) has become a strongly expanding sector of PV technology in the past two decades, whereby the physical properties of organic semi-conductors are fundamentally different from their inorganic counterparts. Even though tremendous improvements of OPV performance have been achieved, a thorough understanding of the relationships between on the one hand the electronic structure of the components and the processing conditions and on the other hand the resulting crystalline structure as well as the electrical performance, is to a large extent still lacking. Developing such relationships is thus a key challenge that will allow to boost device performance and commercial viability. 

During the rapid development of OPVs, poly(3,4- ethylenedioxithiophene) (PEDOT) has been recognized as the most promising and model prototypical semicrystalline photoactive semiconducting polymer. The main objectives of the proposed research are to generate insight in structure development and to unravel the structure-property relationships at different length scales in PEDOT suspensions. These suspensions are the starting material in the production of OPVs and the final electrical conductivity of the latter is largely dependent on the crystallization of PEDOT from its suspension. In this work, ethylene glycol (EG) is chosen as the solvent, in which PEDOT forms stable suspensions.  As the microstructure development at various length scales is essential to tune the resulting electrical conductivity of OPVs, the aim of the research will be to tune the crystallinity, crystalline size and long-range orientation of PEDOT to generate long ranged π-π stacked PEDOT chains, under both quiescent conditions as well as by applying shear.  The study will be one step towards the goal of a more comprehensive framework that unravels the structural paradigms of materials used in optoelectronic applications because of its simplicity and versatility.