07.  High Efficiency Materials for Solid‐State Lighting

Significant technological advancements in semiconductor materials used to manufacture Light Emitting Diodes (LEDs) for general illumination products have produced remarkable improvements in device performance, lifetime and stability along with sizeable reductions in manufacturing costs.  Similarly, comparable advancements in electronic organic materials used in Organic Light Emitting Diodes (OLEDs) have also been realized since the initial introduction of white phosphorescent devices over two decades ago.  These impressive advancements in materials science and in contributing fields such as engineering, physics and chemistry, have helped to successfully introduce very energy efficient and high quality white light sources to practical general illumination products at affordable costs.   While these advancements are both technically advanced and have unquestionably helped to make the solid‐state transformation in general illumination a reality, development of vital new materials are required to harvest the full economic and performance potential of these transformative lighting technologies. 
 
There are notable opportunities for significant cost reductions and product performance improvements possible with the advent of new materials across a wide spectrum of solid‐state lighting (SSL) technologies.  It 
is widely believed that special scientific challenges associated with each of these materials systems remain and are specifically of interest under this topic.  The following subtask descriptions highlight a few opportunities that are of special interest to the DOE’s Solid‐State Lighting program.  Much more technical information about these high priority research and development challenges can be found on the program’s comprehensive website:   http://www1.eere.energy.gov/buildings/ssl/ in the form of numerous technical topical reports, roundtable summaries and program roadmaps. 
 
Grant applications are sought in the following subtopics:  

a. Efficiency and Performance Advancements Phosphor Systems 
 
Many constituent materials are used in the manufacture of phosphor‐converted LEDs (pcLEDs) and while these components perform well, there are important opportunities for device performance improvement and manufacturing cost reductions.  Among the materials systems commercially used in down converting and potentially also for up conversion with the most potential for price and performance improvement are certain rare earth phosphor formulations.  Although SSL uses far less phosphor material than is used in legacy lighting products and are therefore less of a concern as a critical material, there are important performance improvements sought that are thought to lead to commercial manufacture of phosphor systems that are efficient yet more tolerant of operation at elevated temperatures for extremely long periods of time.   Some new phosphors, such as those generally classified as Nitrides for example, are much more tolerant of operation at high temperatures and luminous flux but their manufacture and cost limits their wide spread use especially in certain high volume, first cost driven markets such as residential or “A‐Line” lamp products.  Also, there are important gaps in existing down‐conversion spectrum in both color and efficiency especially at certain pump wavelengths.  As a result, some pcLEDs are less comparable to more familiar continuous emission legacy lighting products such as those that follow black body radiation parameters.  Up‐converting phosphors or quantum‐splitting phosphors also represent opportunities for pcLED device performance improvement but are today, not a practical addition in any known pcLED design.  Even though the performance improvements possible with these approaches may be small, there may be opportunities to integrate these materials systems into existing or new phosphor systems or activators at minimal cost but with important performance or color quality improvements. 
 
Questions – Contact: James R. Brodrick, james.brodrick@hq.doe.gov  

 

b. Alternative Photonic Materials 
 
Alternative color shifting solutions are presently under development that represents potential substitutes or replacements for traditional rare earth phosphor systems used in SSL products.  The most popular alternatives are Quantum Dots (QDs) and Nano‐Phosphors (NP).  While still very nascent, there exist many technical aspects of how these systems might be used effectively as a viable high efficiency, long‐lived alternative to conventional phosphors.  For example, in comparison to commercial phosphor systems QDs are less efficient and experience a variety of non‐radiative loss mechanisms.  The loss mechanisms are not fully understood but any reduction of the non‐radiative losses in these materials will improve their 27 efficiency and potentially, service life at elevated flux density and temperature.  Development of a better
understanding of non‐radiative losses and other fundamental phenomena could lead to new materials and alloys that could be used to dramatically improve the performance of these structures by increasing the device conversion efficiency, lifetime or possibly emission line width.  Similarly, out coupling efficiency and beam management can be effected by NPs or other structures resulting in improved optical performance.  These additions may interact favorably with other components in the LED or OLED design architecture in such a way as to provide longer, more temperature tolerant performance at affordable incremental cost.  
 
Questions – Contact: James R. Brodrick, james.brodrick@hq.doe.gov  

 

c. Emitter Materials 
 
The state‐of‐the‐art emitter materials systems for both LEDs and OLEDs have become somewhat standardized especially in the extensively researched and mass‐produced III‐Nitride alloys.  Even though
these systems can be used today to manufacture economical, energy efficient lighting products, there remains ample room for fundamental materials improvement.  In LED systems for example, a number of technical challenges such as droop and materials defects that arise as a consequence of the lattice constant mismatch between the emitter film and the substrate that it is deposited on.  These conspire to limit device efficiency, lifetime and yield.  In OLED systems, stable, long‐life blue emitters, effects of compositional impurities, environmental contamination, current introduction and electrode transparency still remain as fundamental materials challenges that limit achievement of maximum efficacy, extraordinary lifetime and low cost of manufacture.  Improvements in our understanding of these and similar fundamental effects may lead to the development of new materials that would further improve and advance market share of these important lighting technologies well beyond today’s present levels. 
 
The intent of this topic is to encourage innovative material science development or composite solutions that will enable SSL products to perform at their theoretically predicted maxima in the long run and meet or exceed the aggressive device performance goals established by the DOE in the SSL Multi‐Year Program Plan (MYPP) available for download at http://www1.eere.energy.gov/buildings/ssl/.  Responsive proposals must succinctly address one or more of the key R&D challenges described fully in the SSL MYPP.  Innovations that address manufacturing technology and cost of LEDs while simultaneously addressing the fundamental materials challenges such as those described here as they pertain to general illumination applications are especially welcome. The key metric for judging responsiveness of all proposals however, will be commercialization potential and the prospect of making a lasting and positive impact on the rapidly evolving SSL industry resulting in better quality LEDs at reduced cost. Proposals that include technical risk are encouraged provided they articulate a viable plan to retire such risk during the Phase I period of performance with appropriate proof of principle demonstration.  Projects that result in important intellectual property arebespecially valuable as they may provide future revenue in the form of royalties or cross‐licenses to the benefit small business or participating technology transfer office. 
 
Questions – Contact: James R. Brodrick, james.brodrick@hq.doe.gov