Third-Generation Organic Light Emitting Materials

Since Kodak scientist Dr. Ching W. Tang discovered that sending an electrical current through a carbon compound caused these materials to glow, dozens of companies and institutions have built on Kodak's findings in pursuit of display applications. Research continues to focus on perfecting materials to produce better color, require less power and last longer.

The first color discovered in early organic light emitting diode (OLED) research was green. By 1989 the Kodak research team demonstrated fluorescent dyes, or "dopants," to boost the efficiency and control of color output. Kodak scientists also were instrumental in establishing the architecture for active matrix (AM) OLED displays. These and passive matrix (PM) displays comprise layers of organic materials between glass and metal. When a charge stimulates these layers, they emit light as they relax. Red, green, and blue materials exhibit different color properties and energy efficiencies. Combined in full-color OLED systems, each material's properties may complement or compensate for the others' performance. In other words, full-color display performance is greater than the sum of the parts.

In recent years, Kodak has made strides in new materials, from electron transport materials to emitting substances. This May, at the Society for Information Display conference, Kodak unveiled third-generation organic materials that are more colorful, require less power, and last longer than their predecessors.

In combination, the new materials measure up to the best full-color OLED displays yet, in terms of color, power and lifetime. Building on decades of color science expertise and display research, Kodak improved its red system to offer good red effects with triple the efficiency of the previous system, so that red is no longer the most power-hungry color in a full-color, active matrix OLED device. The new green dopant has slightly truer hue and is lighter than the second-generation green dopant - that is, perceptibly brighter than the second-generation green dopant relative to the brightness of another similarly illuminated area that appears to be white.

The new blue dopant offers the truest color and longest life of blue materials available. Historically, blue organic materials have been the most difficult to create. They have faded more quickly than red and green materials, and tended toward greener shades that are closer to cyan than true blue. Kodak's new blue material demonstrates the industry's best blue effects in full-color active matrix applications. The blue registers 57 percent more chroma than second-generation materials, for a purer, more vibrant blue with a better hue that is less green. As a result, in full-color displays, the new blue makes possible the purest, most vibrant blues, magentas and purples ever.

Improved efficiency in the "right" single color can make full-color systems more power-efficient, as well. Because the human eye is better at converting power to brightness for the green portion of the visible spectrum, full-color device designs can take advantage of gains in the luminous efficiency of new green materials. With gains in efficiency across all three color channels, the new green material is now the color that consumes the most energy. Yet the eye's ability to convert power to brightness for shades of green makes this the best use of the luminance "budget" in any third-generation full-color OLED device.

In a full-color system made of the new materials, more equitable power consumption per color channel also reduces total power consumption. Predictive testing showed that in a full-color AM OLED system, third-generation materials should use less than two-thirds the power needed to drive an equivalent display comprising second-generation materials (Table 1). Full-color passive matrix systems also show a reduction in power requirements.

As a system, the new OLED materials from Kodak provide active and passive matrix displays that present images with more vibrant color and more enduring performance than ever. In fact, the color gamut and brightness possible in third-generation, full-color OLED displays exceed even LCD display capabilities. In the past, OLED materials produced better reds, yellows and greens, while LCD displays outperformed OLED in blues, magentas and purples. Now, the chroma and hue of the new blue material expand the capacity of OLED technology to display blues, magentas and purples that surpass those currently possible in LCD displays.

This difference is dramatically apparent in Fig. 1, which shows OLED displays' color gamut volume entirely subsumes LCD displays' color gamut volume. Regardless of device format, OLED displays using new organic materials are predicted to outshine LCD devices' performance in every way - a significant improvement to be exploited in next-generation electronic devices.