Regensburg 2016 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 36: Poster Ib

HL 36.7: Poster

Dienstag, 8. März 2016, 15:00–19:00, Poster A

Systematic investigation of charge transfer in organic single crystal interfaces — •Yulia Krupskaya^1,2 and Alberto Morpurgo¹ — ¹DQMP, University of Geneva, Geneva, Switzerland — ²IAPP, Dresden University of Technology, Dresden, Germany

Interfaces formed by two different organic semiconductors often exhibit significantly enhanced electrical conductivity, originating from the charge transfer between the constituent materials. The mechanisms driving the charge transfer and determining its amount are still not well studied and not understood microscopically. We have performed a systematic study of single-crystal charge transfer interfaces based on rubrene and F_x-TCNQ, a family of molecules whose electron affinity can be tuned by increasing the fluorine content. The combined analysis of transport and scanning Kelvin probe measurements reveals that the interfacial charge carrier density, resistivity, and activation energy correlate with the electron affinity of F_x-TCNQ molecules, with a higher affinity resulting in larger charge transfer. Although the transport properties can be described consistently and quantitatively using a mobility-edge model, we find that a quantitative analysis of charge transfer in terms of single-particle band diagrams reveals a discrepancy  100 meV in the interfacial energy level alignment. We attribute the discrepancy to phenomena known to affect the energetics of organic semiconductors, which are neglected by a single-particle description, such as molecular relaxation and band-gap renormalization due to screening.

Financial support: DFG KR 4364/1-1 and KR 4364/2-1