Polymer Photovoltaic Cells: Enhanced Efficiencies via a Network of Internal Donor-Acceptor Heterojunctions

The carrier collection efficiency (eta_c) and energy conversion efficiency (eta_e) of polymer photovoltaic cells were improved by blending of the semiconducting polymer with C₆₀ or its functionalized derivatives. Composite films of poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) and fullerenes exhibit eta_c of about 29 percent of electrons per photon and eta_e of about 2.9 percent, efficiencies that are better by more than two orders of magnitude than those that have been achieved with devices made with pure MEH-PPV. The efficient charge separation results from photoinduced electron transfer from the MEH-PPV (as donor) to C₆₀ (as acceptor); the high collection efficiency results from a bicontinuous network of internal donor-acceptor heterojunctions.