We demonstrate a technique for determining the charge collection efficiency ( CC) in bulk heterojunction organic photovoltaic cells (OPVs). To extract CC, we describe an approach to measure the optical absorption efficiency by examining the external quantum efficiency under reverse bias. Using estimates of the exciton diffusion efficiency obtained from photoluminescence quenching measurements, CC is calculated without any input from optical field simulations. For bulk heterojunction OPVs based on the donor-acceptor pairing of boron subphthalocyanine chloride and C 60, a peak CC of (79 ± 2) is realized for films containing 80 wt. C 60 under short-circuit conditions. This optimum composition also coincides with a peak in the fill factor and the short-circuit current density.
Bibliographical noteFunding Information:
This work was supported by the National Science Foundation MRSEC Program under Award Number DMR-0819885 and the University of Minnesota Initiative for Renewable Energy and the Environment. RP also acknowledges support from a University of Minnesota Doctoral Dissertation Fellowship.