sizes. All of this manufacturing, today occurring on Gen 5.5 (1,300 × 1,500 × 0.6 mm) mother glass substrates, is resulting in a precipitous decrease in the cost of OLED technology, while increasing performance, as the industry grows, thereby positioning these early-entry companies to become competitive in producing low-cost, ultrahigh efficiency, easily dimmable OLED sources for the consumer lighting market. Indeed, several companies are concerned only with the lighting applications of OLEDs (i.e., not their uses in displays), such as General Electric, Osram, Moser-Baer, and Philips.

Equipment makers, providing key infrastructure that is required to provide a strong growth in manufacturing, are also starting to take notice of the possibilities for large, developing markets in OLED displays and lighting. Chief among the OLED manufacturing equipment suppliers is Aixtron, SE, the largest producer of MOCVD equipment for LED lighting, which also produces (on still a small scale) organic vapor phase deposition systems for OLEDs. Applied Materials is the world’s largest supplier of equipment for low-temperature polysilicon deposition on glass substrates used as active matrix display drivers (Nathan et al., 2005), and its division Applied Films supplies in-line deposition sources for front-plane OLED display materials deposition. The committee notes, however, that the current lack of a complete tool set for manufacture of OLEDs remains a limiting factor in their widespread and low-cost deployment as lighting sources.

SUMMARY OF OLEO CHALLENGES

Based on the foregoing discussion, phosphorescent WOLEDs provide an unusual opportunity to complement LEDs as an important solution for areal SSL. Yet there remain significant barriers to their adoption, and as a result their development still lags that of inorganic LEDs as the preferred white illumination source

The committee’s findings and recommendations on the major challenges that should be the focus of near-term investment are given below.

Cost Reduction

FINDING: This is potentially the single most important metric to meet in OLED lighting. It requires simplification of device structure, use of ultralow-cost substrates such as metal foils, development of replacements for costly transparent anodes (current technology is indium tin oxide), low-cost encapsulation technologies, and so on. Also, investment in equipment infrastructure is essential for the success of low-cost, manufacturable products. In-line vacuum deposition sources, roll-to-roll processes on flexible substrates, ultrahigh-speed organic vapor phase deposition, and in situ encapsulation techniques will all require substantial infrastructure development.

RECOMMENDATION 3-10: The Department of Energy should aggressively fund the development of all possible routes leading to significant (100×) cost reduction in organic light-emitting diode lighting sources.

Extended Operationat lifetime

FINDING: Extending the lifetime of blue phosphorescent OLEDs is a primary area where investment will have substantial payoff. It involves a combination of advances in the development of new materials, device architectures, encapsulation, and contact technologies, as well as a fundamental advance in the understanding of degradation processes. Interactions between the phosphor and the conductive host will have an influence on mitigating efficiency droop, or the de-excitation of the molecules in the OLED. The mechanisms for thermally induced degradation also require clarification. Encapsulation compatible with flexible, lightweight substrates is also an important area of development.

RECOMMENDATION 3-11: Given the interactions between the phosphor and the conductive host molecules, the Department of Energy should direct studies for determining what chemical structural combinations lead to the most robust materials sets. Fundamental studies of the degradation mechanisms should be carried out both at room and elevated temperatures. Research on understanding contact and ambient degradation routes and their minimization should also be supported.

Low-Cost Light Outcoupting

FINDING: Increased outcoupling remains the single most beneficial route to increasing device efficiency from the current 100 lm/W to nearly three times that value. Methods to achieve this should be inherently very low cost and deployable over very large areas, even in the context of roll-to-roll manufacture. The outcoupling technology should have the additional attributes of being wavelength and intensity independent, and the light source should exhibit no color shifts as the viewing angle is varied from normal to highly oblique. Clearly, a viable outcoupling technology should not otherwise impact or degrade OLED performance.

Addressing the critical challenges for OLED lighting should enable the realization of increased power efficacy and the realization of the targets set by DOE, as shown in Table 3.3.

SUMMARY AND COMPARISON OF LEO AND OLEO SSL

The LED and OLED technologies explored in this chapter provide new, energy-efficient approaches to lighting with exceptional control over the chromaticity and the quality of the light produced. As shown in Table 3.3, both technologies



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