Relating photocurrent, photovoltage, and charge carrier density to the recombination rate in organic photovoltaic cells

The power output of an organic photovoltaic cell (OPV) depends on the relationship between device voltage and charge carrier recombination rate. Suppressing recombination until higher voltages allows for increased photocurrent leading to a concomitant increase in power generated. Despite the important role played by recombination in OPVs, its dependence on voltage remains understudied. This is mainly because most techniques used to measure recombination rates are only applicable under open-circuit conditions. In order to address recombination away from open-circuit, a modified charge extraction technique is used to empirically determine the relationship between charge carrier density and device voltage. This relationship, in conjunction with the device photocurrent density-voltage characteristic, is sufficient to connect the recombination rate at open-circuit to any operating voltage. (C) 2015 AIP Publishing LLC.