Berlin 2015 – scientific programme

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DS: Fachverband Dünne Schichten

DS 7: Organic photovoltaics and electronics - mostly properties of the absorber (jointly with CPP,DS)

DS 7.6: Talk

Monday, March 16, 2015, 18:15–18:30, EW 202

Charge transport: Mobility in organic donor-acceptor blends for photovoltaics — •Johannes Widmer, Julia Oelker, Janine Fischer, Christian Koerner, and Karl Leo — IAPP (Institut für Angewandte Photophysik), TU Dresden, Germany

The charge carrier mobility µ is the key parameter describing charge transport in semiconductors. In amorphous material with predominating hopping transport, the effective mobility is affected by disorder. The resulting µ varies with electric field strength F and charge carrier density n, and is influenced by the layer morphology.

In this contribution, we analyze the mobility of various small molecule organic semiconductors in neat as well as blend layers. The mobility is measured by means of electric potential mapping (POEM), varying the thickness of single carrier devices and evaluating them at constant current density.[1] This measurement technique allows for resolving the field dependence and the density dependence of µ(F, n) independently of each other, separately for electrons and holes.

Substrate heating during the deposition of donor-acceptor blend layers is known to substantially improve the device performance of solar cells, and we show which role the charge carrier mobility plays in this context. Furthermore, the influence of the blend ratio on µ is investigated, which allows for a refined interpretation of the role of the acceptor phase in hole transport. These findings improve the understanding of charge transport in organic solar cells and inspire paths for efficient further improvement of device performance.

[1] Widmer et al., OrgEl 14, p. 3460 (2013)