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

The open-circuit voltage (Voc) of bulk heterojunction solar cells based on polymers and fullerene derivatives is limited to ∼1.15 V by the optical band gap of the fullerene of ∼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 Voc=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 ∼1%.