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The direct measurement of energy barrier height at metal/ polyfluorene derivatives interface by internal photoemission spectroscopy

Published online by Cambridge University Press:  02 February 2011

Eiji Itoh  and
Shinya Takaishi
Eiji Itoh
Affiliation:
Faculty of Engineering, Shinshu University, 4-17-1 Wakasato, Nagano, 380-8553, Japan
Shinya Takaishi
Affiliation:
Faculty of Engineering, Shinshu University, 4-17-1 Wakasato, Nagano, 380-8553, Japan
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Abstract

We have investigated the barrier height for electron injection at the cathode / polyflu-orene derivatives interface by the internal photoemission (IPE) spectroscopy techniques using the “electron only device” structure consisting of TiO2, electron transporting polyimide inter-layer (IL), and polyfluorene derivatives. We also estimated the barrier height by the current analysis based on the Schottky thermal emission current model, and it coincides well to the threshold energy of IPE result only when the energy is lower than 1.1eV. The measured barrier height obtained by IPE linearly increases with both the work-function of cathode materials. However, the slope parameter becomes less than 1 (~0.6) for poly (9,9-dioctylfluorene) (F8) probably due to the interfacial gap states. On the other hand, the slope parameter becomes very small (~0.18) for the poly (9,9-dioctylfluorene)-co- benzo- thiadiazole) (F8BT) probably due to the electron pinning at the cathode/ acceptor interface.

Keywords

electronic structureelectrical propertiespolymer
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1286: Symposium E – Molecular and Hybrid Materials for Electronics and Photonics , 2011 , mrsf10-1286-e11-08
Copyright
Copyright © Materials Research Society 2011

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