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

这个小型企业创新研究(SBIR)第二阶段项目将开发用于蓝光/紫外光发光二极管(LED)的新型渐变折射率(GIN)结构。固态LED(SSLS)是将电能转换为光能的最有效的转换器之一，此外还具有寿命长、可靠性高、功耗低、重量轻、体积小以及优异的抗机械冲击和振动等优点。与传统照明相比，这些显著的优势解释了为什么，根据最近的一项研究，预计未来五年SSL市场的平均增长率约为200%。由于LED是窄带发射器，它们必须与高效的下转换荧光粉耦合，以实现产生白光所需的广泛发射。然而，即使是完美的荧光粉，也不可能实现高效率，除非还存在从LED到荧光粉以及从荧光粉到空气的有效辐射耦合。与输出耦合相关的损耗是由于引起菲涅耳反射和全内反射(TIR)的相邻材料层的折射率(N)的差异造成的。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的高出耦合效率。在第一阶段，成功地证明了EP沉积工艺的可行性，折射率匹配结构的优势已经被证明显著地(~50%)地提高了LED的光提取效率。这一事实在实验和理论上都通过光线跟踪模拟得到了证明。在第二阶段，工作将集中于改进这些蓝光/紫外光LED的结构，以开发高效的下转换技术，使新的固态照明系统成为可能。在商业上，如果SSL技术能够实现这一预期目标，照明行业将发生革命性的变化。潜在的能效可能达到200lm/W，比荧光灯(80lm/W)高2倍以上，比白炽灯(15lm/W)高10倍以上。如果目前照明的总效率约为50Lm/W(介于荧光灯和白炽灯的效率之间)，被总效率为150lm/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倍，从2,350TWh降至780TWh。这将意味着全球用电量减少13%，全球能源使用量和相关碳排放减少2.3%。在美国，预计到2025年，照明可能会减少高达50%的用电量。

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.