Spectroscopic insights into the performance of quantum dot light-emitting diodes
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Introduction: Traditional and emerging LED technologies Beginning with the ancient myth of Prometheus, who stole fire from Mount Olympus, to third millennium technologies, the ability to master artificial light incarnates the very concept of progress and modernity. Throughout history, the impact of artificial lighting on human civilization has been so profound that it has arguably redefined our concepts of time and space, extending our productive time and allowing humankind to explore even the “darkest” corners of our world. Our society relies so heavily on lighting that it dedicates a fifth of global electricity to it, which amounts to over 2,650 TWh of energy. In 2010, the environmental cost associated with the production of this amount of energy was equal to about two billion tons of carbon dioxide emitted in the atmosphere.1 Unfortunately, most of this precious energy is wasted due to the inefficiency of incandescent bulbs that convert only 10% of electricity into visible light, while 90% is dissipated as heat. Fluorescent lamps are less wasteful but still have a conversion efficiency of only 20–30%. The economic advantage of overcoming these limitations, together with a growing awareness
of the harmful effects of carbon emission on global climate, has driven the tremendous effort to develop more efficient and sustainable lighting technologies. Direct conversion of electricity into light using semiconductor-based light-emitting diodes (LEDs) is now universally accepted as the most promising approach to more efficient lighting. Solid-state lighting (SSL) sources such as LEDs demonstrate high brightness, long operational lifetime, and low energy consumption, far surpassing the performance of conventional lighting systems. The LED field is currently dominated by semiconductor quantum-well emitters (based, e.g., on InGaN/ GaN) fabricated via epitaxial methods on crystalline substrates (e.g., sapphire).1 These structures are highly efficient and bright, but their cost-to-light-output ratio (also referred to as the “cost of light”) is at least one-hundred times larger than that of incandescent light bulbs. In addition, traditional semiconductor LEDs are affected by structural defects at the substrate/semiconductor interface due to lattice mismatch and heating during operation, which limits the device area to only 1–2 mm2. Furthermore, harsh conditions required for the fabrication of these structures and difficulties in post-processing
Wan Ki Bae, Chemistry Division, Los Alamos National Laboratory; [email protected] Sergio Brovelli, Department of Materials Science, Università degli Studi di Milano-Bicocca; [email protected] Victor I. Klimov, Chemistry Division, Los Alamos National Laboratory; [email protected] DOI: 10.1557/mrs.2013.182
© 2013 Materials Research Society
MRS BULLETIN • VOLUME 38 • SEPTEMBER 2013 • www.mrs.org/bulletin
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SPECTROSCOPIC INSIGHTS INTO THE PERFORMANCE OF QUANTUM DOT LIGHT-EMITTING DIODES
complicate their use in lightweight, flexible lighting devices and displays. These drawbacks of traditiona
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