Strong interfacial dipole formation with thermal evaporation of lithium cobalt oxide for efficient electron injections

초록

We investigated the electronic structures at the interface of Al/lithium cobalt oxide (LiCoO2)/tris(8-hydoxyquinoline) aluminum (Alq(3)) to elucidate the origin of the electron injection enhancement with the insertion of the LiCoO2 layer in organic light-emitting devices using in situ photoelectron spectroscopy experiments. We discovered that LiCoO2 was decomposed into lithium oxide (Li2O) by thermal evaporation, and only Li2O was deposited on the desired substrate. Li2O forms a strong interfacial dipole, which reduces the surface potential on Alq(3) due to its extremely low work function. As a result, the electron injection barrier was dramatically decreased by the Li2O layer. Furthermore, there is no strong chemical interaction at the interface of Al/Li2O/Alq(3); hence, this would contribute to extend the device lifetime. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4789394]

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