FIGURE 3.8 Light-emitting diode package cost trends. SOURCE: DOE (2011b).
OLEDs are a new source of illumination wherein light is emitted uniformly over a large planar surface. They are primarily deployed today in very large numbers for displays on handheld appliances such as smart phones. The excitement surrounding OLED technology stems from several unique aspects of its manufacture and performance. They are inherently ultrathin film devices that can be deposited on any smooth substrate such as glass, flexible metal foil, or even plastic, and the devices themselves have very high performance: 100 percent internal quantum efficiency, custom tunable color from the blue to the near infrared, and extremely low temperature rise, even when operated at very high brightness. In contrast to the inorganic semiconductor materials used for LEDs, organic materials are predominantly carbon-based, much the same as inks used in printing or dyes used to color fabrics. Hence, in principle they are abundant, inexpensive, and may have limited negative environmental impact. In addition, the materials used in fabricating OLEDs are used in very small quantities and are deposited over large areas using low energy consumption processes owing to their low sublimation temperatures. While there are currently no significant concerns regarding the toxicity of materials used in OLEDs and their packages, the committee can well appreciate that for any technology, what can begin as minor concerns can become more significant as volume of deployment increases. Hence, it may be necessary to monitor the potential negative toxic and environmental effects that OLED lighting may have as the technology becomes adopted to ensure that risks associated with their use is minimal.
The first organic light-emitting device was demonstrated in the 1960s by Pope et al. (1963) and later by Helfrich and Schneider (1965). Sandwiching the organic material anthracene between contact electrodes, blue light was emitted at a relatively high efficiency (a few percent). Unfortunately, the voltage required was very high (~500 V). This situation changed dramatically in 1987 with the first low-voltage OLED. With an efficiency of approximately 1 percent, the voltage was dropped to <10 V, suggesting that a new and potentially efficient light source had been demonstrated (Tang and VanSlyke, 1987). While their first commercial applications of OLEDs have been in ultrathin, full color displays, their currently extremely high efficiency has led laboratories worldwide to explore their applicability as lighting sources.
A simplified OLED structure is shown schematically in Figure 3.9, where the nomenclature used is typical of that used in OLEDs. Here, “ETL” is the organic electron