The investigation of non-doped exciplex blends of 2,4,6-Tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine (PO-T2T), working as the one-electron acceptor molecule, with different electron donors is reported. The emissions of these exciplexes span from the blue to orange-red regions, showing clear contribution from thermally activated delayed fluorescence (TADF) and delayed fluorescence originated from non-geminate recombination of charge carriers created by the dissociation of optically generated exciplexes. We focus our
We fabricated a yellow organic light-emitting diode (OLED) based on the star-shaped donor compound tri(9-hexylcarbazol-3-yl)amine, which provides formation of the interface exciplexes with the iridium(III) bis[4,6-difluorophenyl]-pyridinato-N,C2']picolinate (FIrpic). The exciplex emission is characterized by a broad band and provides a condition to realize the highly effective white OLED. It consists of a combination of the blue phosphorescent emission from the FIrpic complex and a broad efficient delayed fluorescence induced by thermal activation with additional direct phosphorescence from the triplet exciplex formed at the interface. The fabricated exciplex-type device exhibits a high brightness of 38 000 cd/m(2) and a high external quantum efficiency.
A new interface engineering method is demonstrated for the preparation of an efficient white organic light-emitting diode (WOLED) by embedding an ultrathin layer of the novel ambipolar red emissive compound 4,4-difluoro-2,6-di(4-hexylthiopen-2-yl)-1,3,5,7,8-pentamethyl-4-bora-3a,4a-diaza-s-indacene (bThBODIPY) in the exciplex formation region. The compound shows a hole and electron mobility of 3.3 × 10 and 2 × 10 cm V s, respectively, at electric fields higher than 5.3 × 10 V cm. The resulting WOLED exhibited a maximum luminance of 6579 cd m with CIE 1931 color coordinates (0.39; 0.35). The bThBODIPY dye is also demonstrated to be an effective laser dye for a cholesteric liquid crystal (ChLC) laser. New construction of the ChLC laser, by which a flat capillary with an optically isotropic dye solution is sandwiched between two dye-free ChLC cells, provides photonic lasing at a wavelength well matched with that of a dye-doped planar ChLC cell.
The starburst carbazole derivative
and phosphorescent bis-cyclometalated
iridium(III) complex (IC2) were used for the preparation
of multilayered “warm-white” organic light-emitting
diodes (OLEDs), the emission spectra of which are modulated by the
thickness of the phosphorescent layer. It was shown that the electroluminescence
spectra of the fabricated devices are more extended into the visible
region compared with the photoluminescence spectra of both component
materials. The observed extension of the electroluminescence spectra
can be assigned to the phosphorescent emission of the low-energy exciplex
formed at the interface of the emissive layers. The quantum-chemical
calculations performed by the DFT and (TD) DFT methods support the
formation of the low-energy triplet exciplex at the interface of the IC2 layer and the neighboring layer of the starshaped carbazole-based
compound, (4,4′,4″-tris[3-methylphenyl(phenyl)amino]
triphenylamine, tri(9-hexylcarbazol-3-yl)amine (THCA). Indeed, the triplet excited state of such bimolecular complex corresponds
to intermolecular charge transfer between IC2 and THCA. The experimentally observed electrophosphorescence of
these exciplexes is induced by strong spin–orbit coupling in
the THCA:IC2 complexes due to the Ir(III) heavy atom
effect. With dependence on the iridium(III)-complex film thickness
(5–9 nm), the CIE coordinates changed from (0.41, 0.41) to
(0.52, 0.47), corresponding to the warm white and orange color. The
brightness of the fabricated OLEDs at the 15 V bias was in the range
from 500 to 6000 cd/m2.
Diphenilamino-substituted carbazoles were used as guest compounds for the preparation of highly efficient blue organic light-emitting diodes based on the phenomenon of delayed fluorescence. It was shown that the spectra of the delayed fluorescence of host−guest systems are identical to those of the prompt fluorescence and in general coincide with the photoluminescence spectra of the guest films. The congruence of the prompt and delayed fluorescence spectra is explained by the effective intermolecular triplet−singlet (T → S) energy transfer from the excited T states of the host to the S states of the guest molecules. High external electroluminescence efficiency of the fabricated electroluminescent devices, reaching 17%, is comparable to that achieved in phosphorescence-based organic light-emitting diodes.
A new triaryl molecule based on a benzene–benzothiadiazole–benzene core has been applied in a WOLED device. This very simple molecule emits from a combination of emissive states (exciton/electromer/exciplex/electroplex) to give white light with CIE coordinates of (0.38, 0.45) and a colour temperature of 4500 K
The optoelectronic
properties of halide perovskite materials have
fostered their utilization in many applications. Unravelling their
working mechanisms remains challenging because of their mixed ionic–electronic
conductive nature. By registering, with high reproducibility, the
long-time current transients of a set of single-crystal methylammonium
lead tribromide samples, the ion migration process was proved. Sample
biasing experiments (ionic drift), with characteristic times exhibiting
voltage dependence as ∝
V
–3/2
, is interpreted with an ionic migration model obeying a ballistic-like
voltage-dependent mobility (BVM) regime of space-charge-limited current.
Ionic kinetics effectively modify the long-time electronic current,
while the steady-state electronic currents’ behavior is nearly
ohmic. Using the ionic dynamic doping model (IDD) for the recovering
current at zero bias (ion diffusion), the ionic mobility is estimated
to be ∼10
–6
cm
2
V
–1
s
–1
. Our findings suggest that ionic currents
are negligible in comparison to the electronic currents; however,
they influence them via changes in the charge density profile.
To explore the photophysical properties of coordination compounds with bright blue fluorescence an azomethin-zinc complex was synthesized and characterized by various techniques (EA, TG, IR-mass-spectroscopy). The crystal structure was determined by X-ray diffraction analysis. Through thermal characterization this complex was proved to have good thermal stability. Photoluminescence spectra were
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.