Efficient Charge Transport in Polymer Films
A team of researchers at the Umea University/Sweden has shown that efficient charge transport in the perpendicular direction is possible in semiconducting polymer films. Through controlled alignment of the polymer chains and crystallites, charge transport can be increased significantly.
Normally, plastic materials are electrical insulators. However, polymers can transport electrical charges if the main chain contains conjugated double bonds. Conjugated semiconducting polymers are especially well-suited for production of organic optoelectronic components such as solar cells, LEDs and lasers. The polythiophene group of polymers (e.g. P3HT) is one of the most highly studied among semiconducting polymers, since it exhibits optical absorption and can be processed easy into a thin film from solution.
In both organic solar cells and organic LEDS, the charges must be transported perpendicular to the plane of the film. Until now, however, it was not possible to achieve a vertical orientation of the molecular chains. As a result, the vertical mobility of the charge carriers is relatively low, since fast charge transports occurs primarily along the backbone of the polymer. To increase charge carrier mobility, the polymer is normally "doped" - that is, additives are incorporated into the material to improve the electrical properties.
This new work describes a method for aligning the polymer chains vertically. The result is efficient transport of electric charge along the polymer chain's backbone. The high mobility of the electric charges is achieved without chemical doping. According to the report, these results point to a new way of producing more efficient organic electronic components. Since no chemical modification of the polymer is required, manufacturing costs are reduced even further.