High Fill Factor and Open Circuit Voltage in Organic Photovoltaic Cells with Diindenoperylene as Donor Material

Small-molecule photovoltaic cells using diindenoperylene (DIP) as a new donor material in combination with the fullerene C(60) as an electron acceptor are demonstrated. In addition to the successful application in planar and bulk heterojunction devices, a comprehensive analysis including structural studies, the determination of the energy level alignment and electrical transport investigations is given, stressing the correlation between growth conditions, film morphology, and device performance. Due to pronounced crystallinity and a large surface area of DIP films grown at elevated temperature, exceptionally high fill factors of almost 75% are achieved in planar heterojunction cells. Bulk heterojunctions exhibit large-scale phase separation forming a bicontinuous network of both molecular species, which enables efficient exciton dissociation and charge carrier transport. The high ionization potential of DIP and the favorable energy level alignment with the fullerene C(60) yield large open circuit voltages close to 1 V and comparable power conversion efficiencies of about 4% in both cell architectures.