Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “OLEDs”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Stable, High Efficiency White Electrophosphorescent Organic Light Emitting Devices (OLED) by Reduced Molecular Dissociation (Final Report)

We shall pursue radically new strategies for increasing the lifetime of blue phosphorescent light emitting devices (PHOLEDs). Systematically seek robust dopant and host molecular pairs whose energy gaps allow both to participate in charge conduction in the PHOLED Emissive Layer (EML). By tailoring the host/dopant grading profile and extending the emission zone, it is anticipated that these approaches may significantly increase device lifetime while simultaneously increasing its efficiency.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2019

Tuning Singlet and Triplet Excited State Energies and Frontier Orbitals of Imidazole Host/Emitter for Hybrid White OLEDs

In this work, we report hybrid fluorescent/phosphorescent WOLEDs employing blue fluorescent and green and red phosphorescent emitters doped into a host matrix. The fluorescent emitting dopant harnesses all electrically generated high energy singlet excitons for blue emission, and the phosphorescent dopants harvest the remainder of lower-energy triplet excitons for green and red emission. This design requires the singlet state (S1) of the host to be higher than the S1 of the fluorescent dopant so that the singlet excitons generated on the host are transferred to the fluorescent dopant. Furthermore, the triplet state (T1) of the host matrix should be lower than the T1 of the fluorescent dopant so the triplet excitons generated on the fluorescent dopant can be transferred to the host matrix which will then be transferred to the green and red phosphors. To develop a host material that can serve this purpose, we tune the electronic properties of phenanthro[9,10-d]imidazole by incorporating phenyl and/or pyridyl moieties at the N1 and C2 positions of phenanthro[9,10-d]imidazole. This substitution resulted in variety of host materials with different singlet/triplet energies, quantum efficiency and redox values. The resulting phenanthro[9,10-d]imidazoles are employed as host materials for fluorescent and phosphorescent dopants and as neat fluorescent emitters. Monochromatic devices with a fluorescent emitter and the phenanthro[9,10-d]imidazoles as host materials or as neat fluorescent emitter achieved near theoretical maximum efficiency. Finally, efficient three-color hybrid WOLEDs were fabricated using the phenanthro[9,10-d]imidazoles as hosts for a fluorescent dopant or as neat fluorescent emitters and host for green and red phosphors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Orange Fluorescent Ru(III) Complexes Based on 4′-Aryl Substituted 2,2′:6′,2″-Terpyridine for OLEDs Application

A series of ruthenium (III) complexes of the formulae [Ru(4-Mephtpy){sub 2}]Cl{sub 3}(1) [Ru(L{sub 1})], [Ru(3,4,5-tmphtpy){sub 2}]Cl{sub 3}(2) [Ru(L{sub 2})], and [Ru(4-thptpy){sub 2}]Cl{sub 3}(3) [Ru(L{sub 3})], (where L = terpy = 2.2′:6′2″ terpyridine ligands) are synthesized. The complexes were characterized by elemental analyses, spectroscopic and electrochemical data. The density functional theory (DFT) outlines the geometric optimisation and electronic charge transition of these complexes. Photophysical studies describe that the luminescence of Ru(III) complexes is due to electronic transition between the energy levels of singly unoccupied molecular orbitals (SUMO) and singly occupied molecular orbitals (SOMO). It also exhibits the potential charge transfer to π–π* and n–π* states due to MLCT and ILCT processes of the complexes. The observed bands centered at 591 and 620 nm demonstrate that these emissions originated from the transition of SUMO to SOMO energy levels, that is, from the radiative decay from the doublet exciton. Due to the heavy metal effect of Ru(III) ions the photophysical behaviour depends on the MLCT process. In conclusion, that the all three Ru(L{sub 1}-L{sub 3}) complexes are fallen orange emission.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Color optimization of red OLEDs via periodic and gradient deposition rate of fluorescent dopants

We have investigated a method to enhance the light emission efficiency and color tuning for mixture of dyes with varying the growth parameters, during Alq{sub 3}:Nile Red deposition. We used solvent bath and green laser (532 nm) for improvement of the performance of devices. This paper presents two kind of evaporation method, periodic and gradient. We observed that periodic emission layers can greatly improve the device performances such as electroluminescence, chromaticity coordinates, luminance, and reduced the turn on voltage. The periodic 3 structure with evaporation rate of (0.1 → 3 → 2 → 3 → 2 → 0.1 A°/s) has a luminance of 3000 cd/m{sup 2} and maximum efficiency of 1.8 cd/A at 18 V which are the highest values among devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗