QLEDs for displays and solid-state lighting
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olloidal quantum-dots: High-quality visible and infrared light sources Colloidal quantum dots (QDs) are solution-processed nanoscale crystals of semiconducting materials. They emit bright, pure, and tunable colors of light, making them excellent candidates for color centers in next-generation display and solid-state lighting (SSL) technologies.1 As illustrated in Figure 1a and described in the other articles in this issue, their narrow emission spectra can be readily tuned throughout the visible and near-infrared (NIR) spectrum via both quantum size effects and changes in chemical composition.2–4 For visible applications, CdSe-based QDs are currently the material of choice;3,5–7 their saturated emission spans the visible spectrum, delineating a large potential color gamut that approaches that of the human eye8 (Figure 1b). For this reason, QDs have already begun to find commercial applications as optically excited color enhancers: Sony’s 2013 line of Triluminos
liquid crystal display (LCD) televisions (Figure 1b, inset) use edge-mounted red and green QDs from QD Vision to optically down-convert some of the television’s blue LED backlight (absorbing some of the blue light and re-emitting it as red and green light)—optimizing its color balance so that it fulfills >100% of the National Television System Committee (NTSC) television color gamut standard (the color space for broadcast video defined by the NTSC in 1953), compared with ∼70% for conventional LCD screens (Figure 1b).9,10 The result is a television picture with color quality comparable to that of organic LED (OLED) screens, but achieved at the cost of an LCD display. 3M and Nanosys are together exploring similar strategies using their Quantum Dot Enhancement Film.11 Analogous approaches have also been utilized in backlights in high-color-quality white LED SSL, such as QD Vision’s Quantum Light developed in collaboration with Nexxus Lighting.1,8
Geoffrey J. Supran, Massachusetts Institute of Technology; [email protected] Yasuhiro Shirasaki, Massachusetts Institute of Technology; [email protected] Katherine W. Song, Massachusetts Institute of Technology; [email protected] Jean-Michel Caruge, QD Vision; [email protected] Peter T. Kazlas, QD Vision; [email protected] Seth Coe-Sullivan, QD Vision; [email protected] Trisha L. Andrew, University of Wisconsin–Madison; [email protected] Moungi G. Bawendi, Massachusetts Institute of Technology; [email protected] Vladimir Bulovic´, Massachusetts Institute of Technology; [email protected] DOI: 10.1557/mrs.2013.181
© 2013 Materials Research Society
MRS BULLETIN • VOLUME 38 • SEPTEMBER 2013 • www.mrs.org/bulletin
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QLEDS FOR DISPLAYS AND SOLID-STATE LIGHTING
flat-panel display market exceeding USD$80 billion in 2011,22 and with lighting constituting 20% of US electricity consumption,21 the economic and environmental incentives are clear.
Evolution of electrically driven QLEDs A typical electrically driven QD light-emitting device (QLED) comprises two electrodes, which inject charge into a series of active layers sa
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