White-light OLEDs

The fluorescence color converter technique [32] can, in principle, overcome much of this power loss by replacing the white light emitter with a blue-emitting organic stack, and the absorbing filters with green and red fluorescent dyes. Thus when a green pixel is desired, the OLED underneath is turned on and the blui... 

T.K. Hatwar, J.R. Vargas, and V.V. Jarikov, Stabilized white-light-emitting OLED devices employing a stabilizing substituted perylene material, U.S. Patent 2,005,089,714, pp. 21 (2005). 

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... 

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... 

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... 

The luminous efficacy or power efficiency is the lumen output p>er input electrical power of the device. It is measured in lumen per watt (hn/ W) or candela per ampere (cd/ A). It is represented by Jjp. In order to compete with the fluorescent lighting market, the efficiency of OLED sources should be 120 Im/ W or more. To meet the above requirement the OLED sources must have an electrical to optical pxjwer conversion effidency of 34%. For white light with a CRI of 90 the maximum value is 408 Im/W and for a CRI of 100 it is 240 Im/W (Kamtekar 2010). 

Some blue or ultraviolet light from one OLED is used to excite several phosphors, each of which emits a different colour and these different colours are mixed to make a white light with the broadest and richest wavelength spectrum and is called down conversion by phosphors. 

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