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Efficiency enhancement of InP-based inverted QD-LEDs by incorporation of a polyethylenimine modified Al:ZnO layer

: Kim, Y.; Ippen, C.; Fischer, B.; Lange, A.; Wedel, A.


Journal of the Society for Information Display 23 (2015), No.8, pp.377-383
ISSN: 1071-0922
Journal Article
Fraunhofer IAP ()

We report efficiency enhancement of indium phosphide (InP) quantum dot-based light-emitting diodes (QD-LEDs) by using an polyethylenimine (PEI) surface modifier. By adapting a solution processed PEI layer on top of a aluminum doped zinc oxide (Al:ZnO) nanoparticle (NP) film, the leakage current of the inverted device was substantially suppressed. In addition, the electron injection into the conduction band edge (CBE) of InP/ZnSe/ZnS QDs was also facilitated by the low work function (WF) of the Al:ZnO film which was realized by the strong interfacial dipoles of the thin film of PEI. As a result, the charge balance in the inverted devices was controlled by the change of surface roughness, the WF and the thickness of neighboring layers via spin-coating the PEI dissolved in alcohol mixture on the Al:ZnO layer such that the current efficiency was dramatically increased from 0.07 cd/A to 3.17 cd/A. The performance of our device is not comparable to Cd-based devices; however, it shows the great potential for using an interfacial dipole layer to develop highly efficient InP-based inverted QD-LEDs.