AVS 57th International Symposium & Exhibition
    Energy Frontiers Topical Conference Wednesday Sessions
       Session EN+NS-WeM

Paper EN+NS-WeM9
Experimental and Theoretical Investigation of Excitonic Energy Transfer in Organic Photovoltaic Cells

Wednesday, October 20, 2010, 10:40 am, Room Mesilla

Session: Organic Photovoltaics
Presenter: W.A. Luhman, University of Minnesota
Authors: W.A. Luhman, University of Minnesota
R.J. Holmes, University of Minnesota
Correspondent: Click to Email
This work demonstrates a novel approach for measuring the Förster radius of energy transfer between electron donating and accepting materials commonly used in organic photovoltaic cells (OPVs). Typically an exciton must diffuse to an electron donor-acceptor interface in order to be dissociated and contribute to photocurrent. Alternatively, if an exciton in the donor layer is instead able to undergo long-range energy transfer to the acceptor layer, diffusion is no longer required, and dissociation occurs from the acceptor layer. While such processes are surprisingly common in OPVs, they are often incorrectly ignored in measurements of the exciton diffusion length and in models of device performance. In this work, the efficiency of energy transfer between an emissive donor and an absorptive acceptor is investigated using complementary experimental and theoretical techniques. This is accomplished by spatially separating the donor and acceptor materials using a wide energy gap spacer layer to suppress charge transfer, and tracking the donor photoluminescence as a function of spacer layer thickness. Fitting experimental data obtained for a variety of small molecule and polymer donor materials allows for the extraction of Förster radii that correlate very well with predicted values. The effect of energy transfer on device performance and on measurements of the exciton diffusion length is also investigated using the archetypical small molecule donor material boron subphthalocyanine chloride (SubPc). An exciton diffusion length of (7.5±0.4) nm is extracted from photoluminescence quenching experiments that carefully account for the role of energy transfer. These results will ultimately provide insight into the fundamental processes of exciton diffusion and dissociation in OPVs.