Ultra energy efficient III-nitride/polymer hybrid white LEDs using nanotechnology

Lead Research Organisation: University of Strathclyde
Department Name: Physics

Abstract

The last decade has seen dramatic advances in the development of III-nitride light emitters, whose emergence is significantly changing many aspects of our lives. Materials from the III-nitride family can emit light over the complete visible spectrum and a major part of the ultraviolet (UV) and are ideally suited for white light sources. Developments in solid-state lighting are occurring at pace and will lead to near-ultimate lighting sources, likely to be based on III-nitride materials. This will result in a fundamental change in the concept of illumination and has the potential to lead to massive savings in energy, estimated to be equivalent to $112 billion by the year 2020. Such increases in efficiency are increasingly important due to the growing world-wide energy-crisis and threat of global warming.Currently, there are three main approaches for the fabrication of white light emitting diodes (LEDs) needed for solid-state lighting: (1) a package of three LED chips each emitting at a different wavelength (red, green and blue, respectively); (2) a combination of a blue (460 nm) LED with a yellow phosphor pumped by blue light from the LED; (3) a single chip emitting UV light which is absorbed by three phosphors (red, green and blue) and reemitted as a broad spectrum of white light. The first method is ideal for achieving a true white light source, but it is extremely difficult to balance the electro-luminescence intensities of these different colours and there exist a number of fundamental challenges related to the different requirements of the individual LEDs. The performance of current UV-LEDs is far below blue-LEDs and presents a major limitation to the third route. As a result the blue LED+ phosphor approach is maintaining its strong lead for the fabrication of white LEDs with several commercial successes. However, the most promising commercially available white LEDs are based on blue epiwafers with the highest crystal quality, which are thus extremely expensive. This raises the price and thus limits their applications in general illumination. Further development of the technology is also still faced with problems, which are the driving force behind the new type of LED proposed here. We aim to develop a hybrid nanotechnology delivering a new type of ultra high energy efficient white-LED without need for the premium price blue epiwafers. The technologies to be hybridised are arrays of semiconductor nano-rods, with dimensions on the scale of 100s of nanometres, metal nano-particles and polymers. Building on our work demonstrating efficient light emission from conjugated polymers we will optimise these materials for converting blue light to yellow. The new polymers will be used to fill the spaces between nanorods prepared in GaN-based LED structures, maximising the contact between the blue light source and the yellow emitter. Blending silver nano-particles into the polymer will be used to further improve optical performance as a result of a coupling effect between the metal and semiconductor. Relatively thick capping layers usually limit the strength of this effect but the close contact between the polymer/metal blend and the side-walls of the nano-rods enables us to get close to the full benefit.This work will combine the existing strengths at the Sheffield in III-nitride device fabrication and characterisation of III-nitride emitters with those at Strathclyde in polymer chemistry, fundamental optical studies of III-nitrides and characterization of nanostructures, including metal nanoparticles and semiconductors. This combined effort aims to achieve an improved understanding of the fundamental issues in the optical emission processes mentioned above and to optimise fabrication processes of hybrid III-nitride/polymer white LEDs. It will lead to the demonstration of next generation white-LEDs suitable for replacement of conventional light sources in terms of cost and luminous efficacy.

Publications

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Edwards P (2011) Cathodoluminescence nano-characterization of semiconductors in Semiconductor Science and Technology

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Edwards PR (2012) High-resolution cathodoluminescence hyperspectral imaging of nitride nanostructures. in Microscopy and microanalysis : the official journal of Microscopy Society of America, Microbeam Analysis Society, Microscopical Society of Canada

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Findlay NJ (2014) An organic down-converting material for white-light emission from hybrid LEDs. in Advanced materials (Deerfield Beach, Fla.)

 
Description Improvement in performance and understanding of white LEDs and related devices
Exploitation Route To be added
Sectors Other

 
Description Joint research with SHEFFIELD UNIVERSITY 
Organisation University of Sheffield
Country United Kingdom 
Sector Academic/University 
PI Contribution University of Strathclyde researchers worked on this project with researchers from SHEFFIELD UNIVERSITY
Start Year 2010
 
Description Theme leader for SUPA Condensed Matter and Materials 
Organisation The Scottish Universities Physics Alliance (SUPA)
Country United Kingdom 
Sector Academic/University 
PI Contribution Chair : Membership of external research organisation : Theme leader for SUPA Condensed Matter and Materials
Start Year 2008
 
Description Theme leader for SUPA Condensed Matter and Materials 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact Chair : Membership of external research organisation : Theme leader for SUPA Condensed Matter and Materials
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Not recorded
Year(s) Of Engagement Activity 2008