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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Creation of a U.S. Phosphorescent OLED Lighting Panel Manufacturing Facility

Universal Display Corporation (UDC) has pioneered high efficacy phosphorescent OLED (PHOLED™) technology to enable the realization of an exciting new form of high quality, energy saving solid-date lighting. In laboratory test devices, we have demonstrated greater than 100 lm/W conversion efficacy. In this program, Universal Display will demonstrate the scalability of its proprietary UniversalPHOLED technology and materials for the manufacture of white OLED lighting panels that meet commercial lighting targets. Moser Baer Technologies will design and build a U.S.- based pilot facility. The objective of this project is to establish a pilot phosphorescent OLED (PHOLED) manufacturing line in the U.S. Our goal is that at the end of the project, prototype lighting panels could be provided to U.S. luminaire manufacturers for incorporation into products to facilitate the testing of design concepts and to gauge customer acceptance, so as to facilitate the growth of the embryonic U.S. OLED lighting industry. In addition, the team will provide a cost of ownership analysis to quantify production costs including OLED performance metrics which relate to OLED cost such as yield, materials usage, cycle time, substrate area, and capital depreciation. This project was part of a new DOE initiative designed to help establish and maintain U.S. leadership in this program will support key DOE objectives by showing a path to meet Department of Energy Solid-State Lighting Manufacturing Roadmap cost targets, as well as meeting its efficiency targets by demonstrating the energy saving potential of our technology through the realization of greater than 76 lm/W OLED lighting panels by 2012.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2019

Enhanced Light Extraction from Low Cost White OLEDs Fabricated on Novel Patterned Substrates” (Final Report)

Organic LEDs (OLEDs) are a very attractive emerging solid state lighting (SSL) technology. Currently, one of the main challenges is to increase the extraction of the light generated inside the OLED into the forward (viewing) hemisphere. In conventional OLEDs fabricated on a transparent flat anode coated on glass the outcoupling factor is only about 20%. About 50% of the light is lost at the metal cathode (surface plasmon excitation), and waveguided internally in the organic layers and the transparent anode. Another ~30% is waveguided in the substrate to its edges. The research addressed this issue of outcoupling by evaluating OLEDs fabricated on corrugated plastic substrates manufactured in a cost-effective approach. It demonstrated that the outcoupling from such OLEDs can exceed 50% by mitigating plasmon–related loss and internal waveguiding, even without the addition of a microlens array or a hemispherical lens, either of which extracts the light trapped in the substrate. Simulations conducted in parallel with the experimental effort demonstrated how the corrugation assists in the outcoupling. The project also evaluated the role of the corrugation pitch and height in determining the outcoupling factor and other properties of the OLEDs. The technical effectiveness and economic feasibility of the project lie in the patterning of the extracting plastic substrates in an approach that is scalable to roll-to-roll (R2R) manufacturing. R2R processes are drastically lower-cost than batch or single-unit fabrication. The corrugated plastic substrates studied are part of an integrated substrate that includes also a microlens array at the air-side of the substrate and a conductive electrode. The project that was a university-industry collaboration is of major benefit to the public as it demonstrates the feasibility of manufacturing highly efficient OLEDs for SSL in a R2R process, which would drastically reduce the manufacturing cost and increase production in the USA. SSL is efficient and environmentally-friendly. It reduces electricity consumption, and hence lighting cost.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2019

Printed Anodes and Internal Light Extraction Layers on Flexible Glass to Create Cost Effective and High Efficacy Bendable OLED Lighting Panels

In this project, OLEDWorks developed a high efficacy and cost-effective flexible OLED lighting system which could reduce the cost of OLED light by introducing a combination of printable and scalable scattering type internal light extraction (ILE) and transparent conductive silver nanowire technologies that are compatible with roll-to-roll (R2R) processing methods. High efficacy was achieved by co-optimization of the internal light extraction, silver nanowire and ITO anodes, and stacked white OLED structure to reduce unwanted absorption, increase the outcoupling efficiency, and lower the OLED voltage. At the end of Phase I of this project a power efficacy of 90 lm/W was demonstrated in a flexible OLED lighting device based on ultrathin bendable glass. Without much additional work, the milestone of 100 lm/W is certainly within reach, and with further work on light extraction and white OLED materials, we believe 120 lm/W or higher is achievable within the next few years.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2022

Low refractive index OLEDs for practical high-efficiency outcoupling. Final report

Improving OLED light extraction is a significant on-going challenge for the OLED lighting industry. The goal of this program was to explore the potential to improve internal light extraction in a manufacturable way by lowering the refractive index of the OLED stack through dilution with an electrically-inert, low refractive index molecule. We accomplished this goal, identifying a small molecule that can be co-evaporated in the hole transport layer of OLEDs at high loading to reduce the refractive index by 0.2-0.3 refractive index units without degrading charge transport. Implementing this dilution molecule in the hole transport layer of a range of single and multi-stack OLEDs, we demonstrated the ability to improve their internal light extraction by up to ~35% without increasing their drive voltage or reducing their operational lifetime. Importantly, these findings extend to state-of-the-art device architectures with proprietary OLED materials.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2018

Low Cost Corrugated Substrates for High Efficiency OLEDs (Final Report)

The external quantum efficiency (EQE) of a planar OLED is limited to 25%. Around 75% of the light is trapped in the substrate, waveguided and SPP modes. In this project, we demonstrated that nano-structures can significantly improve the EQE of OLEDs. The objective is to improve the EQE to 70% using corrugated substrate, low index layer incorporation and micro lens arrays. We conducted optical study of the operating devices using ARES measurement, and used the result to guide the design of corrugated substrates as well as the OLED stack for better performance. During the first year of the program, we have demonstrated over 60% EQE in a corrugated green OLED with half-ball lens for light extraction. By comparing, the optical characteristics of OLEDs fabricated on single and poly crystal corrugated structures, we confirm that the enhancement using corrugated substrates comes from waveguided and SPP modes extraction. To push the device EQE to 70%, further optimization of the corrugated substrate is needed. The extraction of waveguided and SPP modes are influenced by the corrugation pitch, depth and profile. Therefore, we developed a series of processes to precisely control the corrugation morphology. Through comparison of different corrugated substrates, we observed that while an abrupt surface profile results in stronger mode extraction, it also introduces strong leakage current; while a smooth profile are less efficient in mode extraction, it preserves the quality of an OLED. Based on these observations, we conclude that a single crystal hole corrugation results in optimum EQE % and low leakage current when planarized with PEDOT. To improve the extraction of waveguided mode, we also introduce a low index contrast layer (ICL) to increase the index contrast between corrugated ITO and glass interface. We optimized our recipe for the index contrast layer processing and reduced its refractive index from 1.50 to 1.38. As a result, the optimized device shows 47.6% EQE, which is 1.64 times higher than the reference planar device. By extracting the substrate mode with a hemispherical lens, we obtained an EQE of 71.6%, which is a 2.46 times enhancement. The cross-section SEM image reveals the high EQE is due to the formation of an air gap at the interface of the ICL, resulting in an increase of the index contrast to Δn ~ 1. We use angle-resolved electroluminescence spectroscopy (ARES) to demonstrate that the ICL improves the diffraction efficiency at the ITO/glass interface, extracts TM, TE waveguide and SPP mode more efficiently, and leads to the observed high efficiency. We also address the directional emission issue with the single crystalline microlens arrays (MLAs) by fabricating polycrystalline MLAs. The process uses colloidal assembly method to create a mono-layer of silica spheres, then uses PDMS stamps to replicate the pattern for multi-use imprinting. The MLAs are close-packed in short range but have random orientations in the long range. This avoids stronger extraction along the optical axes of single crystal MLAs and prevents the directional emission issue. We also demonstrate that the color shift induced by the corrugation can be minimized using MLAs. In this scenario, the MLAs work as diffuser to randomize the directional emission from extracted waveguide and SPP modes.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2018

Enhanced Light Extraction from OLEDs Fabricated on Patterned Plastic Substrates

A key scientific and technological challenge in organic light-emitting diodes (OLEDs) is enhancing the light outcoupling factor η out , which is typically <20%. This paper reports experimental and modeling results of a promising approach to strongly increase η out by fabricating OLEDs on novel flexible nanopatterned substrates that result in a >2× enhancement in green phosphorescent OLEDs (PhOLEDs) fabricated on corrugated polycarbonate (PC). The external quantum efficiency (EQE) reaches 50% (meaning ηout ≥50%); it increases 2.6x relative to a glass/ITO device and 2× relative to devices on glass/poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) or flat PC/PEDOT:PSS. A significant enhancement is also observed for blue PhOLEDs with EQE 1.7× relative to flat PC. The corrugated PC substrates are fabricated efficiently and cost-effectively by direct room-temperature molding. These substrates successfully reduce photon losses due to trapping/waveguiding in the organic+anode layers and possibly substrate, and losses to plasmons at the metal cathode. Focused ion beam gauged the conformality of the OLEDs. Dome-shaped convex nanopatterns with height of ~280–400 nm and pitch ~750–800 nm were found to be optimal. Lastly, substrate design and layer thickness simulations, reported first for patterned devices, agree with the experimental results that present a promising method to mitigate photon loss paths in OLEDs.

36 MATERIALS SCIENCE↗
DOE OSTI2022

OLEDs on planarized light outcoupling-enhancing structures in plastic

Light extraction from OLEDs remains a challenge. While consumer demand for OLEDs in display technology continues to grow as prices decline, commercial use of OLEDs in solid state lighting (SSL) applications is lagging due to low light extraction, which results in low efficiency. Previous studies have been directed toward increasing the light extraction factor η out , but cost effective approaches that will enable high throughput and potential upscaling, as well as elucidation of the extraction process, are still lagging. One promising approach is the use of buried light extraction enhancing patterns that are planarized with a high refractive index (RI) layer. When adding substrate mode extracting means, the highest external quantum efficiencies (EQEs) were achieved using a complex approach of planarized vacuum nano holes. Here we present η out -enhancing planarized extraction structures (PES) in plastic. While plastic substrates currently present long-term stability issues and other drawbacks, as we show, they provide a tool for simple, inexpensive, and rapid generation of various enhancing structures that importantly can be transferred to the preferred rigid and flexible glass substrates. Moreover, plastic substrates are attractive for biomedical applications. The successful structures we present are easily scalable periodic corrugations, e.g., with pitch a ~ 4.25 µm and pitch/depth ratio a/h ~2.4 planarized by a layer of RI ~1.9, resulting in maximal EQEs exceeding 60% for a green OLED and 48.5% for a white OLED. Comparable increased EQEs were achieved for structures with a ~ 15 and 16 µm, and a/h ~ 2.1 and 4, respectively. Enhanced extraction was also observed with a very simply fabricated quasiperiodic nanohole array, and surprisingly, with a random shallow design. The latter is at variance with simulations based on diffraction only. Results are discussed in terms of a, h, and structural parameters together with scattering matrix simulations to assess the effect of various PES parameters and the nanoparticle-embedded planarizing layer on η out . The experiments and simulations indicate contributions of diffraction, reflection, and scattering to EQE enhancement.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Increasing the Stability of Deep Blue Phosphor‐Sensitized OLEDs Using the Polariton‐Enhanced Purcell Effect

Abstract The stability of efficient, deep blue organic light‐emitting diodes (OLEDs) remains a major challenge in the field of organic electronics. Poor device stability originates from the high probability for destructive non‐radiative triplet exciton annihilation events. Phosphor‐sensitized fluorescence (PSF) is proposed to achieve an efficient, deep blue color by energy transfer from phosphors to fluorophores. Recently, the polariton‐enhanced Purcell (PEP) effect is introduced to decrease the triplet radiative lifetime and density, resulting in an increase in blue phosphorescent OLED lifetime. Here, the PEP effect is introduced to enhance the stability of the PSF‐OLEDs. It is shown that the PEP effect increases all radiative decay rates of the phosphors and fluorophores, leading to a reduction in the triplet annihilation events. Using a Pt‐complex phosphor sensitizer and a so‐called multi‐resonance fluorescent emitter in a PEP cavity, a 3.1‐fold lifetime increase is observed at a current density ofJ= 10 mA cm −2 , reduced EQE roll‐off and deep blue color with Commission Internationale de l'Eclairage coordinates of (0.13, 0.09). The PEP effect maximally extends PSF‐OLED lifetimes in devices with the highest triplet‐to‐singlet energy transfer rates. Moreover, this work suggests that the benefits of PEPs apply to all triplet‐based OLEDs.

Chemistry↗
DOE OSTI2014

OLED panel with fuses

Embodiments may provide a first device that may comprise a substrate, a plurality of conductive bus lines disposed over the substrate, and a plurality of OLED circuit elements disposed on the substrate, where each of the OLED circuit elements comprises one and only one pixel electrically connected in series with a fuse. Each pixel may further comprise a first electrode, a second electrode, and an organic electroluminescent (EL) material disposed between the first and the second electrodes. The fuse of each of the plurality of OLED circuit elements may electrically connect each of the OLED circuit elements to at least one of the plurality of bus lines. Each of the plurality of bus lines may be electrically connected to a plurality of OLED circuit elements that are commonly addressable and at least two of the bus lines may be separately addressable.

42 ENGINEERING↗
DOE OSTI2017

High Performance OLED Panel and Luminaire

In this project, OLEDWorks developed and demonstrated the technology required to produce OLED lighting panels with high energy efficiency and excellent light quality. OLED panels developed in this program produce high quality warm white light with CRI greater than 85 and efficacy up to 80 lumens per watt (LPW). An OLED luminaire employing 24 of the high performance panels produces practical levels of illumination for general lighting, with a flux of over 2200 lumens at 60 LPW. This is a significant advance in the state of the art for OLED solid-state lighting (SSL), which is expected to be a complementary light source to the more advanced LED SSL technology that is rapidly replacing all other traditional forms of lighting.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2019

Understanding, Predicting, and Mitigating Catastrophic Shorts for Improved OLED Lighting Panel Reliability (Final Report)

Catastrophic OLED lighting panel failure due to electrical shorting was a significant reliability challenge facing the industry. The goal of this program was to develop a basic scientific understanding of how incipient shorts in an OLED originate and grow to a catastrophic level, and to develop mitigation strategies that enable the industry to reach the DOE target of 0.01% failure rate. We accomplished this goal, identifying the origin of shorts, understanding how the evolve over time, and ultimately identifying a mitigation strategy that was implemented by our industry partner and demonstrated to completely eliminate catastrophic shorts in production OLED panels. We identified two general classes of panel defect, termed bright spots and hot spots, that respectively originate from indium-tin-oxide agglomerations and microscale organic semiconductor dust particles on the substrate. The former are largely benign whereas the latter can lead to local shunts that grow over time and cause catastrophic failure. We understand the growth process as a self-reinforcing cycle, where shunt-induced heating volatilizes the surrounding organic semiconductor, which in turn expands the shunt and leads to even more heating. Based on these results, we identified several practical strategies to arrest the growth of early-stage shorts or prevent them entirely. These results will reduce the cost and improve the reliability of OLED lighting.

36 MATERIALS SCIENCE↗
DOE OSTI2023

High Efficacy, Long Lifetime Flexible White OLED Lighting Panels

In this project, OLEDWorks and partners made significant progress in advancing OLED light extraction technology. Improving light extraction efficiency remains one of the most important research topics for OLEDs. Current state-of-the-art white OLED products extract only about 50% of the photons that are generated within the device. Promising new light extraction concepts, such as those based on sub electrode micro lens arrays (SEMLAs), were explored in this project with the potential to achieve extraction efficiency of 60% or higher. Flexible thin glass substrates with integrated SEMLAs were successfully fabricated and scaled to large area. When combined with optimized high efficiency stacked white OLED structures, we achieved the program goals of 120 LPW efficacy and long lifetime more than 100,000 hours.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2024

Improved Operational Stability of Blue Phosphorescent OLEDs by Functionalizing Phenyl‐Carbene Groups of Tetradentate Pt(II) Complexes

Abstract Stable and efficient deep‐blue organic light‐emitting diodes (OLEDs) are in high demand for display and lighting applications but are rarely reported due to their poor operational lifetimes. Herein, the study designs and synthesizes two novel N ‐heterocyclic carbene (NHC)‐based tetradentate Pt(II) complexes PtON5‐dtb and PtON5N‐dtb, and thoroughly investigate their electrochemical and photophysical properties. Functionalization of the NHC moieties can increase the metal‐to‐ligand charge transfer ( 1/3 MLCT) characters in their lowest triplet excited‐states, resulting in significantly shortened photoluminescent lifetimes and remarkably improved device performance. A deep blue OLED employing PtON5N‐dtb as an emitter exhibits a narrow spectral bandwidth with a full‐width at half maximum (FWHM) of 30 nm and a CIE y value of 0.17 and demonstrates a maximum external quantum efficiency (EQE) of 20.4% with a small efficiency roll‐off, which maintains a high EQE of 18.5% at 1000 cd m −2 . Moreover, the deep blue OLED also realizes a long‐measured operational lifetime LT 90 (time to 90% of the initial luminance) of 71 hours with an initial brightness of 1134 cd m −2 , corresponding to an estimated device lifetime LT 90 of 85 h at 1000 cd m −2 . This represented an eightfold lifetime improvement for PtON5N‐dtb‐based deep blue OLED compared to PtON7‐dtb in the same device setting.

Li, Guijie↗
DOE OSTI2022

Reducing Spontaneous Orientational Polarization via Semiconductor Dilution Improves OLED Efficiency and Lifetime

Spontaneous orientational polarization (SOP) in the electron-transport layer (ETL) of organic light-emitting diodes (OLEDs) is increasingly recognized as a key factor influencing their performance. Here, we show that SOP is dramatically reduced in the common electron-transport material 2,2',2"-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) by coevaporating it together with medium-density polyethylene. Eliminating SOP from the ETL of blue fluorescent OLEDs in this manner reduces their operating voltage by 0.5 V, increases their external quantum efficiency (EQE) by 30%, and leads to a threefold increase in device lifetime. We show that the EQE and lifetime improvements both originate from reduced exciton-polaron annihilation in the emissive layer, and that this leads to a functional relationship between the two quantities that can be used to quantify the rate of annihilation-induced degradation in the device. Furthermore, these results highlight a substantial opportunity to improve OLED performance by controlling SOP through semiconductor dilution and suggest that this capability can be used to systematically isolate and understand exciton-polaron degradation in the pursuit of stable blue OLEDs.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Approach to Low-Cost High-Efficiency OLED Lighting. Building Technologies Solid State Lighting (SSL) Program Final Report

This project developed an integrated substrate which organic light emitting diode (OLED) panel developers could employ the integrated substrate to fabricate OLED devices with performance and projected cost meeting the MYPP targets of the Solid State Lighting Program of the Department of Energy. The project optimized the composition and processing conditions of the integrated substrate for OLED light extraction efficiency and overall performance. The process was further developed for scale up to a low-cost process and fabrication of prototype samples. The encapsulation of flexible OLEDs based on this integrated substrate was also investigated using commercial flexible barrier films.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2023

Multifunctional Optical Outcouplers for Efficient and Stable White OLEDs (Final Technical Report)

Replacing fluorescence by phosphorescence in OLED-based solid-state lighting can realize the Department of Energy’s efficiency target of 83% Internal Quantum Efficiency (IQE). The principal challenge, however, is to fix the poor stability of phosphorescent blue OLEDs. To address this, we have fabricated novel plasmonic architectures that improve device stability by decreasing the exciton lifetime of the emitters without drastically decreasing the light extraction efficiency. We describe the impact on stability of these structures in high efficiency blue phosphorescent OLEDs. Although the benefit is appreciable, we find that targeting ‘bright’ triplets on phosphorescent emitter molecules is an incomplete solution, and that it is also necessary to stabilize ‘dark’ triplets formed in the host and blocking layers. We demonstrate substantial improvements in stability using the latter approach, and conclude with a discussion of potential approaches to managing dark triplets in OLEDs.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2016

OLED with improved light outcoupling

An OLED may include regions of a material having a refractive index less than that of the substrate, or of the organic region, allowing for emitted light in a waveguide mode to be extracted into air. These regions can be placed adjacent to the emissive regions of an OLED in a direction parallel to the electrodes. The substrate may also be given a nonstandard shape to further improve the conversion of waveguide mode and/or glass mode light to air mode. The outcoupling efficiency of such a device may be up to two to three times the efficiency of a standard OLED. Methods for fabricating such a transparent or top-emitting OLED is also provided.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2018

High efficiency and stable white OLED using a single emitter

The ultimate objective of this project is to develop efficient and stable white OLEDs employing a single emissive material. To deliver this research goal, the project was focused on three main areas including: 1) the development of efficient and stable phosphorescent excimers; 2) the quick screening of phosphorescent excimers in the device settings; and 3) the incorporation of developed phosphorescent excimers in the state-of-the-art OLED settings to maximize the device efficacy and operational lifetime of single-doped WOLEDs. The successful outcome of this project has provided a potential solution to lower the fabrication cost of WOLEDs significantly by decreasing the complexity of device fabrication, increasing the robustness of materials and providing more cost-effective alternates to the state-of-the-art Iridium-based phosphorescent emitters. Moreover, a single-doped WOLED can provide a greater control of emission color by eliminating color aging. This proposed research is a high impact project which will potentially revolutionize OLED lighting technology and expedite the commercialization process of OLED technology for solid state lighting. This project outcomes will contribute to meet the targeted cost of organic solid state lighting set in the DOE MYPP.

42 ENGINEERING↗