New Class of Encapsulants for Blue LEDs

One of the main roadblocks to higher efficiencies, longer lifetimes, and improved brightness for LED light sources is the usage of current silicone-based encapsulant materials which have low thermal conductivities and refractive indices- The former property results in larger than desired temperatures for the encapsulant layer, leading to loss of phosphor efficiency and reduced LED module lifetimes- The latter property reduces the out-coupling efficiency of blue LEDs and forces LED manufacturers to use higher-costs patterned LED chips to extract out all of the available light for high power LED applications- There has been a series of efforts to boost the thermal properties of encapsulants through the usage of various fillers compounds in conventional silicones; however, none has been successful in meeting the desired DOE goals for encapsulant thermal conductivity and refractive index- In this project we will form a novel class of encapsulants for LEDs which, if successful, will enable a significant boost in thermal performance relative to that of silicones, in addition to a large increase in the corresponding refractive index- Taken together the combination of the two will allow up to a 30% increase in the efficacy of white LEDs, a significant drop in the temperature of the encapsulant layer, a corresponding increase in the lifetime of LED modules, and enable LEDs to operate at high power levels without the concomitant loss of efficiency and lifetime-The novel encapsulants will not contain any silicone materials due to their poorer thermal characteristics- New materials will be synthesized, analyzed for performance and then used to form the new encapsulant films- An optimization process involving the formation of a phenomenological model will be employed to determine the proper choice of materials in order to quickly obtain the best material combinations which enable the highest thermal conductivities, with the refractive indices, at minimum, greater than 1-8- Regarding the thermal conductivities, the project goal is ~1-0 W/(m- K), which is a factor of 5 greater than current silicone encapsulant values- In addition to creating advantaged encapsulant films, white LEDs employing conventional phosphors embedded in both the novel encapsulants and silicone-based ones will be formed- The two types of LEDs will be compared for efficacy and thermal performance, with the expectation of obtaining increased white LED performance for those employing the novel encapsulants-Overall by enabling the next generation of encapsulant materials, enhanced LED efficacy, brightness, and lifetimes can be obtained, which will lead to faster adoption of LED lighting, lower energy costs, and further expansion of available LED markets-