Lithium–aluminum contacts for organic light-emitting devices

Abstract

Organic light-emitting devices have been prepared with multilayer Al–Li–Al cathodes in an ultrahigh vacuum molecular beam deposition system. The optimum device characteristics are obtained when there is a single Al layer separating the Li layer from the organic materials. Ab initio molecular dynamics calculations of the Al–Li interaction clarify the role of Al as a blocking layer to Li diffusion into the organic films as well as the behavior of the device when the thickness of this Al interfacial layer is changed.

Interrelation of Work Function and Surface Stability: The Case of BaAl4

“…OLEDs with an alloy interface between the cathode and the polymer have been found to be superior, in terms of lifetime and luminosity, to those with singleelement cathodes. 3,4 Thus the relationship between Φ and stability 5 is crucial. However, it is poorly understood, especially for more complex metals.…”

Disruptive characteristics and lifetime issues of OLEDs

“…61 Intrinsic deteriorations involve problems in the stability of organic thin fi lm, interface between anode and organic layer, excited state stability, movement of ionic impurity, diffusion of transparent electrode metal into emission layer (indium migration mechanism), cation instability, large energy barrier for charge carriers, positive charges accumulation, and width of recombination zone. 56,57,61,63,69,70,[72][73][74][75][76][77] Adachi's group has reported that a large energy barrier for hole injection at the interface of ITO/HTL (hole transporting layer) would lead to large joule heat generation. The produced heat would steadily cause local aggregation of organic molecules such as dimerization and crystallization of an amorphous HTL.…”

“…73 Diffusion of electrode metal ions into the device's organic layers and its effect on device performance have been extensively studied in the last two decades. 62,[75][76][77][78][79] Electrode metal ions were moved due to an electric fi eld constructed by direct current and reduced the device lifetime. 75 Haskal et al 76 reported that the lithium (Li) diffused rapidly into organic materials from a Li/Al cathode, and thus shortened the device lifetime.…”

“…62,[75][76][77][78][79] Electrode metal ions were moved due to an electric fi eld constructed by direct current and reduced the device lifetime. 75 Haskal et al 76 reported that the lithium (Li) diffused rapidly into organic materials from a Li/Al cathode, and thus shortened the device lifetime. Huang et al 77 reported the strong correlation between the retardation of Al diffusion and the recovery of tris-(8-hydroxyquinoline) aluminum (Alq 3 ) and Photoluminescence intensity suggested that diffusion of Al into Alq 3 may be a major mechanism for Al-induced luminescence quenching in Alq 3 based devices.…”

Liquid metals as electrodes in polymer light emitting diodes

“…17 Hasakl et al showed that a buffer layer of Al between lithium and tris͑8-hydroxyquinolino͒aluminum (Alq 3 ) enhances the performance of pLEDs. 4 Note, that after the deposition of an organic material on a metal layer a diffusive layer has also been observed. Huang et al reported that a thin aluminum oxide layer helps to hinder the diffusion of Al into the deposited Alq 3 layer.…”