Assessment of Solid-State Lighting, Phase Two (2017) / Chapter Skim
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3 Assessment of LED and OLED Technologies
3 Assessment of LED and OLED Technologies
Pages 32-55
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From page 32... ...
also reprinted in the Chapter 3 Annexes 3.A and 3.B, "An • Data on commercial, qualified OLED panels remains LED Primer" and "An OLED Primer," respectively. The sparse, and product performance in a given year is primers treat the basic device structure and metrics of device non-uniform, making future projections of progress performance.
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From page 33... ...
develop- drive current density and increased junction tem ment of new applications, capitalizing on increased perature degrade the efficiency of LED output, by light quality and integrated systems, for which the reducing the "power conversion efficiency" (Figure metric of lumens per watt is a secondary goal.
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From page 34... ...
These details are described "efficiency droop," occurring at increased current densities, in the section "Eliminating or Mitigating ‘Current is illustrated in Figure 3.4. As the current density of the Droop.'" Current droop has a particularly strong LED is increased, the external quantum efficiency (EQE, effect for LEDs emitting in the green and accentu- see Annex 3.A)
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From page 35... ...
It appears that there is a variety of interact ing physical processes that take place in the active region of the LED: both electronic transport (the ease which electrons FIGURE 3.4 Schematic of light-emitting diode efficiency droop move through the device) and photon production efficiency with increasing current density.
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From page 36... ...
. While the power conversion efficiency "Improved Epitaxial Growth and Substrates" and of LEDs falls off, or droops, at current densities "The Manufacturing Supply Chain and Economic greater than ~ 10 A/cm2, current lasers reach their Drivers" in Chapter 5.
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From page 37... ...
Researchers at Rensselaer Polytechnic Insti tute are attempting growth of the LED structure on alternative substrates,6 while researchers at OSRAM Overcoming the "Green Gap" have shown the feasibility of an integrated green LED The loss of LED efficiency at higher current densities structure epitaxially grown atop of a blue LED strucaffects LEDs across the spectral range. The green gap is ture: the blue LED "pumps" the green LED, leading a manifestation of the efficiency droop discussed above, to the output of green light.7 but affecting wavelengths in the green spectral region, and • Most commercial SSL products today employ phosoccurring at lower values of current density.
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From page 38... ...
Laser diodes have structure that are similar to LEDs, but the ‘Green Gap.'" also incorporate mirror structures to achieve a natural amplifica- As described in the Introduction, there are different tion of the light output, and high efficiencies at high input powers. approaches or architectures used to produce packaged LED Blue lasers with 30 percent power efficiency have been demon- white lights.
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From page 39... ...
are based on directly integrating progress in narrow-spectral-width phosphors holds great four primary LEDs -- blue, green, amber, and red -- to produce white light. This approach has a number of advantages in achieving subtle tunings of chromatic ity and luminaire efficacy of radiation (LER)
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From page 40... ...
Other challenges for ing the efficiency and performance of LEDs, including epitaxial growth include developing new materials for green efficiency droop and the green gap in efficiency. Although and red LEDs.
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From page 41... ...
efficiency of OLED panels, with high potential anticipated displays for both mobile and TV applications form a rapidly for future improvements.12 The 2013 NRC report identified growing business today, with estimated 2016 revenue of $15 several key technology issues to be addressed for improved billion.13 Planned installations of new G5 (Generation 5) to OLED performance.
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From page 42... ...
The first generally available OLED lighting product in the United States is produced by Acuity Brands (the CHALINATM OLED pendant, Figure 3.11) and is currently sold in Home Depot as a specialty downlight.14 At a selling price of $299 per unit, the cost amounts to $3.75 per square inch of OLED panels.
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From page 43... ...
provides excellent light than one blue stack provides a pathway to further improve quality, eliciting comments from occupants such as "soft," the lifetime of the white OLED, and this also allows shifting "inviting," "desirable uniformity," and "comfortable." The the white spectrum to a higher color temperature. However, project also revealed several performance issues, such as the lack of stable phosphorescent emitters has placed a limit premature failure of some OLED panels due to electrical of only about 40-60 lm/W on the luminous efficacy of these short, drive incompatibility, and related flickering -- evidence current OLED SSL products.
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Glass Challenges and Promises for OLEDs Excellent progress has been made in achieving high Light extraction film OLED efficacy and long operational lifetimes in OLED panels for lighting applications. OLED panels as large as 320 cm × 320 cm are commercially available, with a tandem device FIGURE 3.14 Hybrid fluorescent and phosphorescent three-unit structure and an integrated light extraction layer.
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From page 45... ...
DOE lighting applications. Current OLED panels are primarily has wisely focused on R&D priorities for core technologies used for decorative or specialty luminaires where the cost that address the key technological challenges for highis determined by the luminaire's design or unique features efficiency SSL.
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From page 46... ...
2013. Organic light-emitting diodes with 30% external quantum efficiency based on a horizontally oriented emitter.
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The nitride blue emitters can also be Semiconductor light emitting diodes (LEDs) are a special coupled with phosphors to generate white light, which is kind of electronic device, which emit light upon the applica currently the dominant approach to an SSL technology.
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From page 48... ...
The multiplicity of the quantum wells ensures over-filling of the quantum wells is related to the problems greater light output. Figure 3.A.2 provides some more detail of droop at high current densities.
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A major element of the package is the lens/ current densities, since loss of power due to resistive heating encapsulate assembly. The lens is integrated with a polymer scales as I2R.
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is defined as the ratio of the total optical power output of the LED to the Internal Quantum Efficiency electrical power input. Low resistive power loss, high ηIQE, Not all electrons and holes that are injected into the LED and good design to maximize ηout produce high power effi(e.g., from a battery)
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Applied Physics Letters light-emitting diodes for solid-state lighting. [in English]
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They are inherently ultrathin film devices that can be deposited on any smooth substrate such as glass, flexible metal foil, or even plastic, and the devices themselves have very high performance: 100 percent internal quantum efficiency, custom tunable color from the FIGURE 3.B.1 Archetype organic light-emitting diode structure. blue to the near infrared, and extremely low temperature SOURCE: A.E.
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From page 53... ...
Even with these limitacolor emission being changed from the ultraviolet, through tions, the power efficiency of phosphorescent white organic the blue and green, to the red. In all cases, the light emis- light emitting devices can exceed 150 lm/W, making them sion can be extremely efficient (100 percent conversion of especially attractive for use as efficient lighting sources.
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From page 54... ...
and striped architectures. performance is achieved using a variant of one of the three Hence, the device still achieves 100 percent internal quantum designs in Figure 3.B.3 depicts the striped white organic light efficiency since all excitons are harvested by a combination emitting diode (WOLED)
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From page 55... ...
1999. The times higher quantum efficiency is achieved with this device excitonic singlet-triplet ratio in a semiconducting organic thin film.
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