Characterization of charge transport via in situ potentiometry in bulk heterojunction organic photovoltaic materials

The most promising active material for organic photovoltaic (OPV) cells is the polymer/fullerene bulk heterojunction (BHJ) system, but charge transport and recombination mechanisms in these materials have yet to be completely understood. We report the use of lateral bulk heterojunction devices to perform novel material diagnostics on the BHJ system. Using electron beam lithography, we fabricate devices with up to 24 voltage probes embedded in the channel in order to perform in situ potentiometry. From current vs. voltage measurements performed at a variety of light intensities, we are able to describe the charge transport properties in three distinct regions of a polymer/fullerene BHJ device and determine the dominant recombination mechanism of the OPV material. We note that these are the first such measurements performed on OPV materials. Such measurements will be very useful for materials diagnostics.