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HL: Fachverband Halbleiterphysik

HL 64: Poster: Photovoltaics and Optics

HL 64.15: Poster

Mittwoch, 22. März 2017, 15:00–19:00, P1C

Hole Transport in Low Donor Content Organic Solar Cells — •Donato Spoltore, Andreas Hofacker, Johannes Benduhn, Sascha Ullbrich, Olaf Zeika, Sebastian Schellhammer, Frank Ortmann, and Koen Vandewal — Dresden Integrated Center for Applied Physics and Photonic Materials, George-Bähr Str. 1, 01069 Dresden

Organic solar cells for which a small molecule electron donor is diluted in a fullerene matrix have a reduced density of donor-fullerene contacts, resulting in reduced free carrier recombination and increased open-circuit voltages. In such devices, the low donor concentration prevents the formation of pathways of directly adjacent hole transporting molecules. Despite this, high external quantum efficiencies in the strongly absorbing region of the fullerene can still be reached, suggesting an interesting hole transport mechanism. Here we perform a systematic study of the hole mobilities of 18 donor:C60 blends, where the donors are diluted at ~6 mol% and have varying frontier energy level offsets and relaxation energies. We find that hole mobilities are dominantly rendered by the relaxation energy of the donor allowing the formulation of an empirical law to estimate hole mobilities in low donor content organic solar cells. Surprisingly, the energy offset between the C60 matrix and the donor material shows no contribution indicating the formation of an effective hole transport level. The C60 matrix only adds by a constant contribution to the activation energy of the transport process.