Efficient white OLEDs are becoming attractive as large area light sources for illumination and in future also for general
lighting. We discuss device concepts for white OLEDs and their potential to achieve high efficacy and good lumen- and
color-maintenance at the same time. We focus on OLEDs using a combination of fluorescent blue and phosphorescent
red and green emitters (hybrid OLEDs). Hybrid OLEDs have high efficacy and lifetime in the white to warm white color
region (color points B and A on the black-body-curve). Near illuminant A efficacy values of 28-29 lm/W without optical
out-coupling can be achieved with a hybrid OLED. The external quantum efficiency (EQE) is 14%. A typical color
rendering index (CRI) is 84. Recent results for monochrome OLEDs and for hybrid OLED stacks are presented.
Organic light emitting diodes (OLEDs) provide potential for power-efficient large area light sources that combine
revolutionary properties. They are thin and flat and in addition they can be transparent, colour-tuneable, or flexible. We
review the state of the art in white OLEDs and present performance data for three-colour hybrid white OLEDs on indexmatched
substrates. With improved optical outcoupling 45 lm/W are achieved. Using a half-sphere to collect all the light
that is in the substrate results in 80 lm/W. Optical modelling supports the experimental work. For decorative applications
features like transparency and colour tuning are very appealing. We show results on transparent white OLEDs and two
ways to come to a colour-variable OLED. These are lateral separation of different colours in a striped design and direct
vertical stacking of the different emitting layers. For a striped colour tuneable OLED 36 lm/W are achieved in white with
improved optical outcoupling.
The RC2LED is a substrate emitting OLED which has three additional interference layers between the ITO
electrode and the glass substrate. This creates two resonant optical cavities. The RC2LED has 2 resonant
optical cavities. The first cavity is also present in regular devices and is formed by metal/organic layers/ITO.
The second cavity is formed by 3 additional layers: a high refractive index layer (Nb2O5), a low refractive index
layer (SiO2) and a high refractive index layer (Nb2O5). The additional layers introduce a strong wavelength
dependent improvement of the extraction efficiency compared to the OLED without the additional layers.
Our simulations show an improvement of the extraction efficiency of over 70% over a wavelength range of
75 nm compared to an OLED without the 3 layers. Light extraction is worse compared to the reference OLED
for wavelengths outside this wavelength range. the when compared to the OLED. This improvement has been
experimentally verified for a green OLED with an emission between 500nm and 650 nm.
A numerical study shows a relative improvement of 10% for the luminous power efficiency of a 3 color white
OLED with the additional layers. The emitted white corresponds with the light emitted by illuminant A. The
WOLED has been composed of a fluorescent blue emitter, green and red phosphorescent emitters.
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