Electronic Design
Architecture May Propel Phosphorescent AMOLEDs Into The Mainstream

Architecture May Propel Phosphorescent AMOLEDs Into The Mainstream

Organic light-emitting diodes (OLEDs) and active-matrix OLEDs (AMOLEDs) have been making some noise for a while. Although they’re finding their way into more and wider markets—particularly mobile displays and televisions—they’re quite young compared to LEDs and LCDs. They’re also still morphing and working out various kinks, particularly lifespan, color, and cost issues.

Even though they’re raising the bars in performance and features, OLED-based designs tend to carry steeper price tags than their LED and LCD counterparts. Several established and emerging technologies are broaching these problems, yet material degradation issues plague AMOLED displays. Also, if manufacturers cut corners in the overall design, the displays cannot be viewed under certain conditions such as direct sunlight. And, AMOLED displays are still pricey.

Phosphorescent Technology

Promising to speed the commercial viability of phosphorescent AMOLEDs, Universal Display Corp. has introduced an all-phosphorescent AMOLED display architecture that relies on a four-color sub-pixel design. Along with red, green, and blue, the architecture adds a light blue sub-pixel, the fourth color, to the conventional RGB configuration (see the figure).

Interestingly, one of the main problems associated with phosphorescent OLEDs (PHOLEDs) is the shorter functional life of the blue-pixel material. Red and green PHOLEDs perform without degradation for as much as tens of thousands of hours longer than blue PHOLEDs. This characteristic can lead to the early distortion of picture quality, leading to very disappointed customers.

But according to the folks at Universal Display, the introduction of the fourth component, the light blue subpixel, can significantly extend the operational lifetime of an OLED display while reducing display power consumption by as much as 33% compared to a standard RGB OLED display using a fluorescent blue subpixel.

Apparently, the light-blue subpixel is more energy-efficient and offers a longer life than the standard, deep blue. It provides a significant portion of the blue-emission requirement, reducing the stress on the deep-blue subpixel.

In collaboration with professor Jin Jang of Kyung Hee University and Samsung Mobile Display, Universal Display demonstrated the four-subpixel architecture at May’s SID 2010 in Seattle via a 2.5-in., all-phosphorescent AMOLED display.

“This architecture 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,” said Steven V. Abramson, president and chief executive officer of Universal Display.

For example, Universal Display has demonstrated a 15- by 15-cm white phosphorescent OLED lighting panel using the light-blue PHOLED emitter system. According to the company, the panel delivers the most energy-efficient performance at this scale. It emits a warm white light with a color rendering index of 87 and a correlated color temperature of 3055 K.

Other features include a luminous efficacy of 50 lumens/W using an optical out-coupling treatment with a 1.5× enhancement factor and an operating lifetime of approximately 10,000 hours to 70% of an initial luminance of 1000 cd/m2. The company further asserts that with up to four times the efficiency of conventional OLED technology, its PHOLED technology and materials enable white OLEDs that have the potential to meet Energy Star requirements for solid-state lighting.

OLEDs Rising

According to Universal Display, OLEDs can offer higher performance than existing flat-panel display technologies. In addition to yielding thinner and lighter end products, OLEDs are designed to enable faster response times, wider viewing angles, better color performance, and higher contrast ratios. Also, paired with the company’s PHOLED technology, OLEDs are expected to be far more energy efficient than their LCD predecessors.

Presently, Universal Display claims that its proprietary PHOLED technology will deliver four times the efficiency of conventional OLED technologies. No stranger to the market, the technology can be found in a plethora of cell phones, multimedia players, and various displays.

What about cost? Universal believes OLEDs have the potential to be cost effective because they have fewer processing steps and require less materials and external equipment than LCDs. Hopefully, as OLED manufacturing technologies mature, OLED production yields should continue to improve. We shall see.

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