PROGRAM AREA OVERVIEW

22. SOLID STATE INORGANIC AND ORGANIC LIGHT EMITTING DIODES FOR GENERAL LIGHTING

The current generation of solid state lighting (SSL) products (monochromatic) are commercially viable and, in some limited instances, may contribute to energy conservation. However, they are most often used in applications that do not produce the large energy conservation results sought by the DOE for general illumination. The DOE has engaged the rapidly expanding SSL industry and research community in several workshops^(1,2,3,5) that have identified high priority research needs. The objective of this topic is to encourage small business participation in addressing these needs, in order to overcome the significant technical challenges that restrict the application of SSL to only relatively low luminous output products. Grant applications are sought only in the following subtopics:

a. High Efficiency Visible and Near UV (>380 nm) Semiconductor Materials for LED-Based General Illumination Technology—Current nitride compound semiconductors are incapable of achieving the price and performance targets to be competitive in general illumination applications, primarily due to limitations in materials and packaging. In particular, significant advances in the basic materials technology associated with visible and near UV light emitting diodes (LEDs) will be needed for current devices to achieve performance characteristics beyond their present limitations of 50 to 80 lumens per watt (LPW). These advances not only must produce the substantial gains in light production efficiency, but also must reduce the significant costs normally associated with the complex and labor intensive epitaxial growth required to produce these devices.

Grant applications are sought to develop significant improvements in conventional nitride systems performance (e.g., >80 LPW) or explore novel material systems to achieve this goal. Approaches of interest include (1) advancements in P-doping efficiency and novel charge introduction structures, which may produce significant fundamental improvements to existing materials systems; and (2) advancements in high purity process materials and growth structures, which also may improve device performance by limiting the photon inhibiting processes thought to be associated with defects, dislocations, and other crystalline artifacts. In order to achieve practical solutions, grant applications must demonstrate that improvements by several orders of magnitude, in the price and performance of these devices, are likely. Anticipated device performance should be compared to benchmark devices available today (i.e., Luxeon III⁽⁴⁾).

b. Advanced Architectures and Designs for High Power Conversion Efficiency Emitters—Grant applications are sought to develop advanced device architectures and designs that optimize both the electrical transport and optical properties of SSL devices, in order to achieve long-term efficiencies in excess of 160 lumens per watt, leading to meaningful energy savings. Areas of interest include (1) more advanced light emitting designs such as micro-cavities, photonic lattices, quantum dots, and edge emitting and vertical-cavity laser structures; and (2) fundamental advancements and novel innovations associated with chip-level architectures and high power conversion efficiencies, believed by many to be the key for producing significant increases in power handling capability. Grant applications may be directed at any advanced architecture approach for achieving the desired increase in power capability including, but not limited to, novel chip scaling, production of practical and cost efficient multi-color chips, or building resonant cavity devices such as lasers or directional emitters. Grant applications also must include a complete discussion of anticipated price and performance impacts compared to baseline devices available today⁽⁴⁾.

c. High Efficiency, Low-Voltage, Stable Materials for OLED-Based General Illumination Technology—Today, the designs for organic light emitting diodes (OLEDs) used for general illumination purposes are usually derived from designs associated with display applications. This is not ideal. General illumination OLEDs will require different price and performance levels to perform as viable alternatives to conventional luminous sources. Current OLED materials simply do not have the efficiency or lifetime performance necessary to qualify them as viable candidates for the demanding general illumination market. Estimates of lifetime and efficiencies necessary for OLED-based general illumination are roughly 50,000 hours and 100 lumens per watt (LPW), respectively. However, state-of-the-art white OLEDs (at 850 cd/m²) have a lifetime and efficiency of approximately only 500 hours and 5 LPW, respectively. In addition, innovative device structures and materials are needed to reduce high-luminance (~1000 cd/m²) drive voltages from 10-20V to 4-5V. To realize the full potential of OLED technology, new materials and systems are needed that offer the promise of vastly improved efficiency and stability.

Experimental OLED systems in the laboratory have already achieved luminous efficiencies of in excess of 200 LPW with external quantum efficiencies greater than 10%. However, many challenging technical issues still remain to achieve the targeted OLED lifetime and performance at the relatively high intensities needed for general illumination applications. A recent workshop ⁽⁵⁾ was held in Salt Lake City, UT (sponsored by DOE, Basic Energy Sciences) and a list of high priority research issues was identified. Therefore, grant applications are sought to achieve the above OLED requirements for general illumination, by addressing one or more of these high priority issues: (1) carrier injection, related to ohmic and non-ohmic contacts; (2) spin effects, such as singlets versus triplets, and their relative formation cross-sections; (3) interface chemistry and physics, such as organic/metal, organic/dielectric and organic/organic; (4) quenching of electroluminescence processes, such as quenching by metallic electrodes, by injected polarons and triplets, and by electric field; (5) theory and modeling; (6) morphology effects on OLED performance; (7) light extraction theory and techniques for improvement, including novel approaches that provide a substantial increase over the 10% extraction that is characteristic of today’s devices; (8) the relationship between constituent material purity and OLED performance; and (9) new ways of producing the requisite white light, i.e., a more thorough understanding of how OLED materials systems produce broad visible emissions.

Grant applications must include a complete discussion of the anticipated improvement in efficiency, the potential impacts on cost and lifetime, and the compatibility with practical methods of current distribution and controls. Although packaging considerations should be considered, they should not be the primary subject of grant applications submitted under this topic.

References:

1. Illuminating the Challenges: Solid State Lighting Program Planning Workshop Report, Crystal City, VA, November 13-14, 2003, prepared by Navigant Consulting, Inc. for U.S. DOE Office of Energy Efficiency and Renewable Energy, February 2004. (Full text available at: http://www.netl.doe.gov/ssl/PDFs/SSLWorkshopReport.pdf)

2. Organic Light Emitting Diodes (OLEDs) for General Illumination Update 2002: An Optoelectronics Industry Development Association (OIDA) Technology Roadmap, OIDA, August, 2002. (Full text available at: http://www.netl.doe.gov/ssl/workshop/Report%20OLED%20August%202002_1.pdf)

3. Light Emitting Diodes (LEDs) for General Illumination: An OIDA Technology Roadmap Update 2002, OIDA, November 2002. (Full text available at: http://www.netl.doe.gov/ssl/workshop/Report%20led%20November%202002a_1.pdf)

4. Lumileds, Lighting, U.S. LLC, Product information Web site for Luxeon III solid-state light sources. (See: http://lumileds.com/products. A number of manufacturers supply LEDs, but for consistency of comparison among applications, please consult the data for this product.)

5. Fundamental Research Needs in Organic Electronic Materials, Executive Summary of U.S. DOE Basic Energy Sciences/Energy Efficiency and Renewable Energy OLED Workshop, Salt Lake City, Utah, May 23-25, 2003. (Summary available at: http://www.netl.doe.gov/ssl/PDFs/DOE_BES_SummaryJune%202004.pdf)

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