A high-throughput method for probing exciton dissociation at organic donor-acceptor interfaces

In the organic molecular solids, electrons and holes are bound together to form excitons. Effective dissociation of these excitons at interfaces is critical for applications such as photovoltaics and photosensing. Here, we develop an interface-sensitive ultrafast spectroscopy method that utilizes a graphene field effect transistor as an ultrafast electric-field sensor to measure the exciton dissociation dynamics at organic donor-acceptor interfaces. Compared to other interface-sensitive techniques such as time-resolved non-linear optical spectroscopy, our method has a much-reduced measurement time and can be easily adapted to a large variety of interfaces. Hence, it can be developed into a high throughput screening tool to evaluate the effectiveness of charge separation in a large number of interfaces. Using a typical organic donor-acceptor interface, ZnPc/C₆₀, as an example, we demonstrate how this method can be used to distinguish the coherent charge separation from delocalized CT excitons and the thermal-activated charge separation from bound, localized CT excitons.