Over the past several years, CdTe-based photovoltaics have undergone a revolution. CdTe is a mature PV technology, spanning over 60 years. For a decade, CdTe record cell efficiencies remained dormant at 16.7%, far behind multi-crystalline Silicon (mc-Si) as well as the competing thin film PV technology, CuInxGa1-xSe2 (CIGS). Recently, the CdTe field reawakened as multiple fundamental breakthroughs pushed the record cell efficiencies from 16.7% in 2011 to 21.0%, announced recently1. CdTe now stands as the most efficient, polycrystalline, thin-film PV system with ample room for further optimization.
Here we present recent progress in developing efficient wet-coated organic light-emitting
devices (OLEDs) for lighting applications. In particular, we describe a novel approach
for building efficient wet-coated dye-doped blue phosphorescent devices. Further, a novel
approach for achieving arbitrary emission patterning for OLEDs is discussed. This approach
utilizes a photo-induced chemical doping strategy for selectively activating charge injection
materials, thus enabling devices with arbitrary emission patterning. This approach may provide
a simple, low cost path towards specialty lighting and signage applications for OLED
technology.
Organic light-emitting devices (OLEDs) have shown great promise for general lighting applications. Over the past several years, tremendous progress has been made in improving performance attributes such as light quality, efficacy and lifetime of OLEDs. However, achieving the low cost manufacturing potential of OLEDs, another stringent requirement to enable lighting applications, has so far not been well addressed and explored. Here, we describe a vacuum-free, direct lamination process that could reduce OLED manufacturing costs substantially below what is currently possible. With this technique, OLEDs can be made by laminating an anode component to a separately engineered cathode component using a roll laminator. When coupled with a solution-based chemical n-doping strategy to enable efficient electron injection from an inert cathode into polymeric organic semiconductors, the lamination technique is able to produce high performance OLEDs with efficiency comparable to conventionally fabricated devices utilizing a vacuum-deposited, reactive metal cathode.
A series of phenol-capped, oligofluorenes having 2,3,5 and 7 fluorene units and a statistical oligomer with an average of about 10 fluorene units was prepared. In a similar fashion, phenol-capped oligomers having various charge-transporting moieties incorporated into the oligomeric structures were prepared. Polymers were prepared from the oligomers by various linking reactions involving the phenol groups. Trends in the optical and electrical properties as a function of oligomer length will be reported. Device data for this family of emissive copolymers indicates that charge mobility increases with conjugation length, and can be as good as or better than that of an analogous fluorene homopolymer.
Bilayers of aluminum (Al) and alkali fluoride (such as sodium fluoride) are well-known top cathode contacts for organic light-emitting devices (OLEDs) in which the alkali fluoride is inserted in between the Al and organic materials. However, the configuration, to date, has never been successfully applied as bottom cathode contacts. In this article, we describe a novel bilayer bottom cathode contact for OLEDs utilizing the same materials but with a reversed structure, i.e. the Al rather than the alkali fluoride contacts the organic material. Electron-only devices were fabricated showing enhanced electron injection from this bottom contact with respect to an Al-only contact. Kelvin probe, X-ray photoelectron spectroscopy, Auger electron spectroscopy experiments and thermodynamic calculations suggest that the enhancement results from n-doping of the organic material by dissociated alkali metals.
One of the limitations on OLED performance is the optical extraction efficiency, ηex, which is the ratio of light generated within the device to light emitted into the ambient. Ideally ηex is equal to unity. Typical estimates for this efficiency factor in OLEDs range between 0.17-0.5. We present a simple radiative transport model that quantifies the effect of volumetric light scattering on light output in terms of a small set of readily measured parameters. Our methodology is sufficiently general to parameterize and describe many of the light extraction schemes found in the literature. We will present a set of model calculations using parameters typical of many OLEDs, and show that the introduction of light scattering sites within the otherwise transparent substrate can increase light extraction efficiencies by at least a factor of 1.4. We also present experimental data to validate our analysis and demonstrate a high level of agreement between model and experiment.
OLED technology has improved to the point where it is now possible to envision developing OLEDs as a low cost solid state light source. In order to realize this, significant advances have to be made in device efficiency, lifetime at high brightness, high throughput fabrication, and the generation of illumination quality white light. In this talk, the requirements for general lighting will be reviewed and various approaches to meeting them will be outlined. Emphasis will be placed on a new monolithic series-connected OLED design architecture that promises scalability without high fabrication cost or design complexity.
OLED technology has improved to the point where it is now possible to envision developing OLEDs as a low cost solid state light source. In order to realize this, significant advances have to be made in device efficiency, lifetime at high brightness, high throughput fabrication, and the generation of illumination quality white light. In this talk, a down conversion method of generating white light is demonstrated and shown to be capable of generating illumination quality white light over the full range of color temperatures required for lighting. It is also demonstrated that, due to the presence of light scattering, the down-conversion method can actually increase the overall device power efficiency.
27 August 2007 | San Diego, California, United States
Organic Light Emitting Materials and Devices X
13 August 2006 | San Diego, California, United States
Organic Light-Emitting Materials and Devices IX
31 July 2005 | San Diego, California, United States
Organic Light-Emitting Materials and Devices VIII
2 August 2004 | Denver, Colorado, United States
Organic Light-Emitting Materials and Devices VII
4 August 2003 | San Diego, California, United States
Course Instructor
SC353: OIDA Roadmap on Solid State Lighting
The business of lighting sources is in a phase of significant flux. The simultaneous goals of addressing both energy and pollution reduction is driving change for the underlying technology behind lighting sources. This presentation by leading industry experts examines some of the trends and their implications to lighting and new applications of optoelectronics.
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