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Light blue strengthens white OLEDs

03 Jun 2010

The future make-up of white OLED pixels could be a four way mix of red, green, blue and light blue.

A new light-blue phosphorescent OLED emitter developed by Universal Display Corporation (UDC) could provide performance benefits for both display and lighting applications. According to UDC, the emitter offers key performance advances for displays when used in a new four sub-pixel format and for lighting may accelerate the introduction of initial commercial products where high-efficacy, warm white emission is important.

To showcase the potential of the emitter, UDC has presented details of a 2.5 inch all-phosphorescent active matrix OLED (AMOLED) display that uses a four-colour sub-pixel design. The format adds a light blue sub-pixel to the conventional red-green-blue (RGB) configuration.

The introduction of a light blue sub-pixel is said to significantly extend the operational lifetime of an OLED display and reduce the display's power consumption by as much as 33%, compared with an RGB OLED display using a fluorescent blue sub-pixel.

"Our team has demonstrated an innovative display pixel architecture to leverage the power efficiency advantage of phosphorescence," said Steven Abramson, president and CEO of UDC. "This can extend operational lifetime and has the potential to accelerate and expand the commercialization of all-phosphorescent OLED displays to meet increasing consumer demand for displays with low power consumption and enhanced performance."

The four sub-pixel design relies on a more energy-efficient, longer-lived light-blue sub-pixel to satisfy a significant portion of the blue emission requirement, compared with a conventional RGB pixel format using phosphorescent red and green sub-pixels and a fluorescent blue sub-pixel. By adding a light-blue sub-pixel, the stress on the deep-blue sub-pixel is lessened.

According to UDC, the light-blue emitter offers CIE coordinates of (0.17, 0.37) and a peak wavelength of 472 nm. It also provides a luminous efficiency of >45 candelas per ampere, corresponding to >20% external quantum efficiency at 1000 candelas per square metre (cd/m2). Under accelerated test conditions this new emitter system is also said to demonstrate an operating lifetime of approximately 9000 hours, to 50% of an initial luminance of 1000 cd/m2.

Turning to lighting applications, UDC has used its light-blue emitter system to create a 15 × 15 cm all-phosphorescent white OLED lighting panel. The panel is believed to have the most energy-efficient performance, at this scale, reported to date.

The company says that the panel emits a warm white light with a colour rendering index of 87 and a correlated colour temperature of 3055 K. It also has a luminous efficacy of 50 lumens per watt using an optical out-coupling treatment with a modest 1.5× enhancement factor.

With an operating lifetime of approximately 10,000 hours to 70% of an initial luminance of 1000 cd/m2, UDC claims that this panel performance has the potential to meet the requirements for a number of initial commercial niche OLED lighting applications, and is an important step toward white OLED panel performance that achieves Energy Star targets.

"With up to four times the efficiency of conventional OLED technology, our proprietary PHOLED technology and materials have enabled the demonstration of power-efficient, white OLEDs that have the potential to meet Energy Star requirements for solid-state lighting," said Abramson. "Manufacturers can now employ an all-PHOLED materials set for white OLEDs to achieve power efficiency, spectral and lifetime targets for a variety of initial commercial niche lighting products."

Iridian Spectral TechnologiesPhoton Lines LtdHyperion OpticsHÜBNER PhotonicsCeNing Optics Co LtdBerkeley Nucleonics CorporationSPECTROGON AB
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