High Open-Circuit Voltage Solar Cells Based on New Thieno[3,4-c]pyrrole-4,6-dione and 2,7-Carbazole Copolymers

New alternating copolymers derived from thieno[3,4-c]pyrrole-4,6-dione (TPD) and 2,7-carbazole moieties have been synthesized by Suzuki cross-coupling reaction and characterized. These polymers combine interesting properties such as good solubility and excellent thermal and air stability. The present studies indicate that the combination of TPD and 2,7-carbazole building blocks can be-a very effective way to lower the HOMO energy level and ultimately to enhance the V-oc of polymer solar cells. The V-oc reported here (up to 1.07 V) is one of the highest observed for polymer:[60]PCBM bulk heterojunction devices, and preliminary results on the photovoltaic devices (power conversion efficiencies up to 1.8%) indicate that performance could probably be improved by increasing the molecular weights and by fine-tuning the electronic properties and the morphology.