Influence of OVPD parameters on the performance of organic solar cells utilizing pentacene/PTCDI absorption layers

As global energy demand is steadily growing, renewable energy generation by solar cells is becoming increasingly important. The use of mono- and polycrystalline silicon solar cells, which nowadays dominate the market, is limited by wafer size, rigidness of substrates and the requirement of large energy amounts for manufacturing. Organic solar cells (OSC) have the potential to overcome these limitations; especially organic vapor phase deposition (OVPD) technology offers the possibility of reproducible, large-scale production at low temperatures and on flexible substrates. We report on planar heterojunction OSC utilizing an active layer of pentacene/N, N'-ditridecylperylene-3, 4, 9, 10-tetracarboxylic diimide (PTCDI) fabricated by an Aixtron Gen-1 OVPD tool. The influence of substrate temperature was studied using atomic force microscopy (AFM) on single layers and bilayers. In addition electrical characterization with and without illumination of fully processed solar cells which utilize different cathode layers was carried out. AFM images indicate that crystallization of pentacene layers can be widely influenced by substrate temperature, a PTCDI-C13H27 layer atop of these covers the crystallites. Open-circuit voltage was found to be 0.47 V and short-circuit current densities beyond 0.8 mA/cm2 were measured under a spectrum close to AM 1.5 with 100 mW/cm2. Fill factors were determined to be as high as 44 %.