Claudia Michaela Goldmann

OLEDs for lighting applications

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.

White OLEDs for lighting applications

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.

66.3: Hybrid White OLEDs for General Lighting

OLEDs for general lighting require both high efficacy and good lumen maintenance. Hybrid stacks combining fluorescent blue and phosphorescent red and green emitters are a very good choice for both long lifetime and good efficacy values: 31 lm/W are demonstrated for a cold white color point. 44 lm /W are measured with improved out-coupling (ILO) using a scattering foil and 60 lm/W are demonstrated using a macro-extractor for light out-coupling. For warm white we realized 34 lm/W (with ILO 45 lm/W and 64 lm /W using a macro-extractor). LT50 lumen maintenance is for both stacks better than 30,000 hours.

52.3: OLEDs for Lighting Applications

OLEDs for lighting applications require the combination of several properties at the same time: Large emission area, high brightness, high efficiency, long lifetime, good color stability at different brightness levels, and low cost. In order to fulfill these demands, several OLED architecture concepts are under investigation: Hybrid layered OLEDs, stacked OLEDs, pixel-OLEDs. To achieve good color stability the diode-units used for stacking have to be optimized. The talk focuses on hybrid OLEDs and their properties. In this context we demonstrate a phosphorescent yellow diode (combination of red and green emitters) which has an efficacy between 50 and 60 lm/W without improved light out-coupling (ILO) and excellent color stability. Such highly optimized OLED architectures have to be combined with suitable optical out-coupling techniques to make OLEDs ready for lighting. Optical out-coupling techniques are briefly reviewed. We demonstrate a concept for extracting more light of an OLED using low refractive index hole transport layers.