SBIR Phase II: Efficient Light Out Coupling from AlGaN Light Emitting Diodes

该小型企业创新研究（SBIR）第二阶段项目将开发用于蓝色/紫外发光二极管（LED）的新型渐变折射率（GIN）结构。 固态LED（SSL）是电能转化为光的最有效的转换器之一，并且还具有寿命长、可靠性好、功耗低、重量轻、尺寸小和耐机械冲击和振动的优点。根据最近的一项研究，SSL市场的平均增长率预计在未来五年内将达到每年200%左右。由于LED是窄带发射器，因此必须将其与高效的下转换荧光粉耦合，以实现产生白色光所需的广泛发射。然而，即使对于完美的磷光体，也将不能实现高效率，除非还存在从LED到磷光体中以及从磷光体到空气的辐射的有效外耦合。与外耦合相关联的所产生的损耗是由于相邻材料层的折射率（n）的差异引起的菲涅耳反射（Fresnel Reflections）和全内反射（TIR）。 在第一阶段，研究团队开发了独特的材料结构和电泳（EP）沉积工艺，有望以低成本实现LED的高输出耦合效率。在阶段I期间，EP沉积工艺的可行性已被成功证明，并且折射率匹配结构的优点已被证明可显著（~50%）提高LED中的光提取效率。 这一事实在实验和理论上都得到了证明，使用光线跟踪模拟。在第二阶段，工作将集中在改善这些结构的蓝色/紫外线LED的开发有效的下转换技术，使新的固态照明系统。商业上，如果SSL技术可以实现这一预期目标，照明行业将发生革命性变化。潜在的200lm/W的效率是可能的，比荧光灯（80lm/W）好2倍以上，比白炽灯（15lm/W）好10倍以上。如果目前的照明总效率约为50 lm/W（介于荧光灯和白炽灯的效率之间），被总效率为150 lm/W（略低于目标）的半导体照明所取代，那么目前用于照明的电力将减少三分之一，从2,350 TWh减少到780 TWh。这将意味着全球用电量减少13%，全球能源使用和相关碳排放量减少2.3%。在美国，预计到2025年，由于照明而导致的电力消耗的潜在减少将高达50%。

This Small Business Innovation Research (SBIR) Phase II project will develop novel graded-index (GIN) structures for blue/UV light emitting diodes (LEDs). Solidstate LEDs (SSLs) are among the most efficient converters of electrical energy into light and additionally have the advantages of long lifetime, excellent reliability, low power consumption, light weight, small size and excellent resistance to mechanical shock andvibration. These significant benefits over conventional lighting explain why, according to a recent study, the average growth rate for the SSL market is expected to be around 200% per year for the next five years.Since LEDs are narrow-band emitters, they must be coupled to an efficient downconverting phosphor in order to achieve the broad emission necessary for the generation of white light. However, even for a perfect phosphor, high efficiency will not be achievable unless there is also efficient out-coupling of radiation from the LED into the phosphor and from the phosphor to air. The resulting losses associated with outcoupling are due to the difference in refractive indices (n) of adjacent material layers that cause Fresnel Reflections and total internal reflection (TIR). In Phase I the research team has developed unique material structures and electrophoretic (EP) deposition process that are expected to realize high out-coupling efficiencies from LEDs at low costs. During Phase I, the feasibility of the EP deposition process has been successfully demonstrated and the advantage of an index-matching structure has been shown to significantly (~50%) improve the light extraction efficiency in LEDs. This fact was demonstrated both experimentally and theoretically using ray tracing simulations. In Phase II the work will focus on refining these structures for blue/UV LED's to develop the efficient down- converting technology for enabling the new solid state lighting systems.Commercially if SSL technology can achieve this projected goal, the lighting industry would be revolutionized. Potentially an efficiency of 200lm/W is possible, more than 2X better than that of fluorescent lamps (80lm/W), and more than 10X better than that of incandescent lamps (15lm/W). If current lighting, with an aggregate efficiency of roughly 50lm/W (in between the efficiencies of fluorescent and incandescent lamps), were replaced by semiconductor lighting with an aggregate efficiency of 150lm/W (somewhat less than the target), then the electricity currently used for illumination would decrease by a factor of three, from 2,350TWh to 780TWh. This would represent a decrease in global electricity use of 13%, and a decrease in global energy use and associated carbon emissions of 2.3%. In the U.S., the potential reduction in electricity consumption due to lighting is expected to be as high as 50% by the year 2025.