127 research outputs found
Bright electroluminescence from a conjugated dendrimer
Journal ArticlePhotoluminescence and electroluminescence (EL) from a conjugated dendrimer consisting of three distyrylbenzene units linked by a central nitrogen atom as core and meta-linked biphenyl units as dendrons were investigated. The conjugated dendrimer emits green light and shows photoluminescence quantum efficiency of 9%. Bright electroluminescence was realized by using bilayer devices with blurred interface, which were fabricated by sequentially spin coating a neat dendrimer and a dendrimer doped with 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD). The devices have the following structure: indium tin oxide/3,4-polyethylenedioxythiothene- polystyrenesulfonate/dendrimer/ dendrimer:PBD/Al. By optimizing the concentration of PBD, the maximum brightness and EL quantum efficiency reach 4100 cd/m2 and 0.17%, respectively. This is the best result reported so far on organic light-emitting diodes using dendrimer as an active material with an Al cathode
A versatile hybrid polyphenylsilane host for highly efficient solution-processed blue and deep blue electrophosphorescence
A universal hybrid polymeric host (PCzSiPh) for blue and deep blue phosphors has been designed and synthesized by incorporating electron-donating carbazole as pendants on a polytetraphenylsilane main chain. The polymer PCzSiPh (4) has a wide bandgap and high triplet energy (ET) because of the tetrahedral geometry of the silicon atom in the tetraphenylsilane backbone. The distinct physical properties of good solubility, combined with high thermal and morphological stability give amorphous and homogenous PCzSiPh films by solution processing. As a result, using PCzSiPh as host with the guest iridium complex TMP-FIrpic gives blue phosphorescent organic light-emitting diodes (PhOLEDs) with overall performance which far exceeds that of a control device with poly(vinylcarbazole) (PVK) host. Notably, FIrpic-based devices exhibit a maximum external quantum efficiency (EQE) of 14.3% (29.3 cd A−1, 10.4 lm W−1) which are comparable to state-of-the-art literature data using polymer hosts for a blue dopant emitter. Moreover, the versatility of PCzSiPh extends to deep blue PhOLEDs using FIr6 and FCNIrpic as dopants, with high efficiencies of 11.3 cd A−1 and 8.6 cd A−1, respectively
Bright electroluminescence from a conjugated dendrimer
Photoluminescence and electroluminescence (EL) from a conjugated dendrimer consisting of three distyrylbenzene units linked by a central nitrogen atom as core and meta-linked biphenyl units as dendrons were investigated. The conjugated dendrimer emits green light and shows photoluminescence quantum efficiency of 9%. Bright electroluminescence was realized by using bilayer devices with blurred interface, which were fabricated by sequentially spin coating a neat dendrimer and a dendrimer doped with 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD). The devices have the following structure: indium tin oxide/3,4-polyethylenedioxythiothene-polystyrenesulfonate/dendrimer/ dendrimer:PBD/Al. By optimizing the concentration of PBD, the maximum brightness and EL quantum efficiency reach 4100 cd/m(2) and 0.17%, respectively. This is the best result reported so far on organic light-emitting diodes using dendrimer as an active material with an Al cathode. (C) 2002 American Institute of Physics
Long-coherence pairing of low-mass conduction electrons in copper-substituted lead apatite
Two entangled qubits emerge as an essential resource for quantum control,
which are normally quantum confined with atomic precision. It seems inhibitive
that in the macroscopic scope collective qubit pairs manifest long coherence
and quantum entanglement, especially at high temperature. Here, we report this
exotic ensemble effect in solid-state sintering lead apatite samples with
copper substitution, which have been repeatedly duplicated with superior
stability and low cost. An extraordinarily low-field absorption signal of cw
electron paramagnetic resonance (EPR) spectroscopy stems from low-mass
conduction electrons implying the coherence of cuprate radicals can be
long-termly protected. The pulsed EPR experiments exhibit triplet Rabi
oscillation from paired cuprate diradicals with the coherence time exceeding 1
microsecond at 85K. We believe these appealing effects are sufficiently
promising to be applied for scalable quantum control and computation.Comment: 16 pages, 4 figure
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Modification of TiO_2 Nanoparticles with Organodiboron Molecules Inducing Stable Surface Ti^(3+) Complex
As one of the most promising semiconductor oxide materials, titanium dioxide (TiO_2) absorbs ultraviolet (UV) light but not visible light. To address this limitation, the introduction of Ti^(3+) defects represents a common strategy to render TiO_2 visible-light-responsive. Unfortunately, current hurdles in Ti^(3+) generation technologies impeded the widespread application of Ti^(3+) modified materials. Herein, we demonstrate a simple and mechanistically distinct approach to generating abundant surface-Ti^(3+) sites without leaving behind oxygen vacancy and sacrificing one-off electron donors. In particular, upon adsorption of organodiboron reagents onto TiO_2 nanoparticles, spontaneous electron injection from the dibron-bound O^(2-) site to adjacent Ti^(4+) site leads to an extremely stable blue surface Ti^(3+)‒O^(-•) complex. Notably, this defect generation protocol is also applicable to other semiconductor oxides including ZnO, SnO_2, Nb_2O_5 and In_2O_3. Furthermore, the as-prepared photoelectronic device using this strategy affords 10^3 fold higher visible light response, and the fabricated perovskite solar cell shows an enhanced performance
Ions-induced Epitaxial Growth of Perovskite Nanocomposites for Highly Efficient Light-Emitting Diodes with EQE Exceeding 30%
Cesium lead bromide (CsPbBr3) is a widely used emitter for perovskite
light-emitting diodes (PeLEDs), benefiting from its large carrier mobility,
high color purity and good thermal stability. However, the three-dimensional
CsPbBr3 films encounter challenges due to their massive intrinsic defects and
weak exciton binding effect, which limited their electroluminescence
efficiency. To address this issue, the prevailing approach is to confine
carriers by reducing dimensionality or size. Nonetheless, this method results
in an increase in surface trap states due to the larger surface-to-volume ratio
and presents difficulties in carrier injection and transport after reducing
lattice splitting to smaller sizes. Here, we successfully achieved proper
control over film crystallization by introducing sodium ions, which facilitate
the epitaxial growth of zero-dimensional Cs4PbBr6 on the surface of CsPbBr3,
forming large grain matrixes where CsPbBr3 is encapsulated by Cs4PbBr6.
Notably, the ions-induced epitaxial growth enables the CsPbBr3 emitter with
significantly reduced trap states, and generates coarsened nanocomposites of
CsPbBr3&Cs4PbBr6 with grain size that surpass the average thickness of the thin
perovskite film, resulting in a wavy surface conducive to light out-coupling.
Additionally, another additive of formamidinium chloride was incorporated to
assist the growth of nanocomposites with larger size and lower defects as well
as better carrier injection and transportation. As a result, our demonstrated
PeLEDs based on the coarsened nanocomposites exhibit low nonradiative
recombination, enhanced light extraction and well-balanced carrier
transportation, leading to high-performance devices. The champion device
achieved an external quantum efficiency of 31.0% at the emission peak of 521 nm
with a narrow full width at half-maximum (FWHM) of 18 nm
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