Dresden 2014 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 117: Organic semiconductors: Material properties (with CPP/DS)
HL 117.8: Talk
Friday, April 4, 2014, 12:00–12:15, POT 051
Direct measurement of the charge carrier mobility in organic donor-acceptor blend in device geometry – including extreme stoichiometry — •Johannes Widmer1, Janine Fischer1, Christian Koerner1, Karl Leo1, and Moritz Riede1,2 — 1Institut für Angewandte Photophysik (IAPP), TU Dresden, Germany — 2Current address: Clarendon Laboratory, UK
Blend layers of an organic donor (D) and a fullerene acceptor (A) are a key component of highly efficient organic solar cells. The charge carrier mobility in the blend sensibly affects the device efficiency concerning transport and recombination of charge carriers.
The applied method “POEM” – potential mapping by thickness variation – is a direct measurement giving model-free experimental access to the effective mobility µ(F, n) as a function of the electric field F and the charge carrier density n. It is based on a novel evaluation strategy for space-charge limited current (SCLC) in single carrier devices in a vertical device geometry.[Widmer et al., Org. El. (2013)]
Here, we apply POEM to characterize the hole transport in D:A blends of small molecules with different blend ratios. The measurements cover common ratios as well as strongly diluted blends with only ≈ 1 % donor content, which are known to yield efficient solar cells. Beyond characterizing disorder and trap states, which influence µ, the POEM measurements reveal that also in the diluted blend effective hole transport is possible, but takes place not only on the donor.
The obtained µ(F, n) functions allow for an advanced understanding of charge transport in D:A blends – also in moderate blend ratios.