Berlin 2015 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 61: Posters III (Organic-inorganic perovskite semiconductors; Organic photovoltaics and electronics; Photovoltaics; Energy science; New materials and concepts)
HL 61.14: Poster
Mittwoch, 18. März 2015, 15:00–20:00, Poster F
Charge-transfer states vs. triplet excited states in organic photovoltaics — •Johannes Benduhn, Donato Spoltore, Christian Körner, and Koen Vandewal — Institut für Angewandte Photophysik, Technische Universität Dresden, D-01062 Dresden, Germany
Charge generation and recombination in organic solar cells occurs via the formation of charge-transfer (CT) states at the donor-acceptor interface. When the energy of the CT state is high, its formation can compete with the formation of triplet states on the donor or acceptor molecule, which can constitute an additional loss mechanism, reducing photo-voltaic performance.
With this work we aim to elucidate under which energetic and kinetic circumstances triplet state formation can be suppressed. Therefore we investigate material systems comprising of C60 as acceptor and a series of phthalocyanine dyes with slight variations in their molecular structure (ZnPc, F4−ZnPc, CuPc, F4−CuPc) as donor. The addition of fluorine allows tuning of the energy of the CT state, resulting in an increased open circuit voltage. Varying the central atom from Zn to Cu enhances inter-system crossing to a triplet excited state on the phthalocyanine molecule. The energy levels of all relevant electronic excited states are determined by sensitive measurements of the external quantum efficiency spectrum. The formation of triplets is quantified by steady state photo-induced absorption at various temperatures.
We find that in the system with a reduced inter-system crossing, charge generation for materials with a high energy CT state is still efficient, even though the triplet state is the lowest energy state.