OLEDs-white light emission

In the vapor-deposited OLED community, a number of approaches have been employed to produce white light emission. White OLEDs have been demonstrated based on multilayer structures, e.g., stacked backlights [153,168], multidoping of single-layer structures [145], phosphorescent monomer-excimer emission layers [169] and on doping of phosphorescent materials into separate bands within the emission zone, called a tri-junction [170]. The trijunction device has produced the highest white OLED efficiency of 16% external quantum efficiency demonstrated thus far [171]. 

One of the concepts used to produce white light emission in OLEDs is based on the energy transfer mechanism from host molecule to guest molecule. The energy transfer in... 

Numerous white OLEDs have been fabricated (Kido et al 1994, 19%, Dodabalapur et al 1994, Yang et al 1997). In the fabrication of full colour display all three primary colours have equal importance but white light emission has drawn particular attention because any desired colour range can be achieved by filtering of white light (Strukeji et al 19%, Zhang et... 

There have been a number of attempts to make OLEDs based on discotic liquid crystals although performance is disappointing probably because of aggregation. Wendorff and co-workers demonstrated monoesters of triphenylene 7, see Table 6.2, in their Colp phase and mainchain polymers of triphenylene in the Coin phase in electroluminescent devices. High electric fields were required, 10 V cm , and the lifetimes of the devices are probably not very long [40,41]. The bilayer devices made by Bock and co-workers, e.g., ITO/triphenylene 8 (hole transporter)/perylene 9 (electron transporter)/aluminium [43,44] exploit materials that have liquid crystal phases above room temperature [42, 43]. Simple variants on these structures were synthesised, which had green, blue and sometimes almost white light emission [44]. 

The EML with a multilayer structure for the lanthanide ions is very different from that of other phosphor materials such as iridium complexes. Multilayer structures with EMLs usually emit hybrid light which is used in white light emitting OLEDs [33]. For lanthanide complexes extremely pure light is achievable, because their emission is due to electronic transitions of... 

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