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DS: Fachverband Dünne Schichten

DS 3: Organic Electronics and Photovoltaics I (Joint Session DS/CPP/HL/O)

DS 3.2: Vortrag

Montag, 22. März 2010, 10:30–10:45, H8

Improved transport properties of p-i-i small molecule solar cells deposited on heated substrates — •Steffen Pfuetzner, Karl Leo, and Moritz Riede — Institut für Angewandte Photophysik, Technische Universität Dresden

To achieve higher efficiencies in organic solar cells, ideally the open circuit voltage (V_OC), fill factor (FF) as well as the short current density (j_SC) have to be improved further. However, in bulk heterojunction (BHJ) solar cells jsc and the FF are typically limited by charge carrier recombination due to transport problems (e.g. low mobility, dead ends) in the BHJ. A suitable way to modify the BHJ layer morphology and to improve solar cell parameters is substrate heating during bulk layer deposition. Furthermore, j_SC can be enhanced by replacing C₆₀ by C₇₀. We show that substrate heating at 90^∘C leads to improved FF and j_SC for a C₆₀ and ZnPc containing BHJ solar cell with the following stack structure: ITO/p-Di-NPD/C₆₀:ZnPc/C₆₀/BPhen/Al. However, in case of similar C₇₀:ZnPc solar cells, no significant improvements are observed. Using SEM we show that the preferential aggregation by heating is completely suppressed by the p-doped underlayer Di-NPD. To force aggregation of the heated C₇₀:ZnPc bulk, 5 nm intrinsic ZnPc layer is deposited on the p-Di-NPD layer and verified by SEM. J-V characteristics show a drop in FF and Voc with the additional interlayer ZnPc. To overcome this problem probably caused by transport barriers to the neighboring layers, experiments with doped ZnPc are carried out.