Maximizing the open-circuit voltage of polymer: Fullerene solar cells

The open-circuit voltage (V(oc)) of bulk heterojunction solar cells based on polymers and fullerene derivatives is limited to similar to 1.15 V by the optical band gap of the fullerene of similar to 1.75 eV and the required 0.6 eV offset for efficient charge generation. In practice this limit has not yet been reached. We present a semiconducting polymer that gives V(oc) = 1.15 V. To reach this value the surface of the hole collecting electrode is modified by UV-ozone, which increases the work function and creates an Ohmic contact. Under simulated AM1.5 conditions optimized cells provide a power conversion efficiency of similar to 1%. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3480598]