Organic thin film photovoltaic cells based on planar and mixed heterojunctions between fullerene and a low bandgap oligothiophene

We present the material alpha-omega-bis-(dicyanovinylen)-sexithiophen (DCV6T) as donor material in organic solar cells. A systematic study on the potential of DCV6T is given for different active layer concepts. DCV6T is a member of a class of acceptor-substituted oligothiophenes, which showed efficiencies of up to 3.4% and open circuit voltages (V(oc)) of 1.0 V, which were recently reported [K. Schulze Adv. Mater. (Weinheim, Ger.) 18, 2875 (2006)]. To verify the potential of the material (DCV6T), organic solar cells with planar heterojunctions, bulk heterojunctions, and a hybrid-planar-mixed heterojunction are investigated. The planar heterojunction solar cells of DCV6T and C60 show the highest V(oc) of 0.90 V. The mixed heterojunction solar cells have improved currents but a lower V(oc) of 0.82 V. The solar cell using the hybrid-planar-mixed heterojunction achieves the best combination of parameters. It has a V(oc) of 0.88 V, a short circuit current (j(sc)) of 5.7 +/- 0.4 mA cm(-2), a fill factor of 41.6%, and a power conversion efficiency of 2.1 +/- 0.2%.