8 research outputs found
Synthesis and Properties of Oxygen-Linked <i>N</i>-Phenylcarbazole Dendrimers
A series of novel oxygen-linked <i>N</i>-phenylcarbazole
(NPC) dendritic wedges (<b>3</b>–<b>5</b>) and
triphenylamine-centered dendrimers (<b>CBD-G0</b> to <b>-G2</b>) have been synthesized and extensively studied. The aryl–oxygen–aryl
(Ar–O–Ar) linkages were established on 3,6-positions
of carbazole and 4-position of <i>N</i>-phenyl group. UV–vis
spectra revealed that the Ar–O–Ar linkage would break
down the π conjugation and make NPC units manifest their individual
absorption moiety. Both steady-state luminescence and fluorescence
decay dynamics at room temperature and 77 K in tetrahydrofuran suggested
that the transfer of energy from the carbazole wedges to the triphenylamine
(TPA) core operates in <b>CBD-G1</b>, so that the luminescence
mainly arises from the core unit. The quenching of the emission from
carbazole wedges by the TPA core becomes less effective as the generation
develops into <b>CBD-G2</b>. The oxidation potential of the
NPC derivatives clearly revealed the mesomeric electron-donating effect
of the oxygen atom and inductive electron-withdrawing effect of the
carbazole unit. The potential gradient could be established on those
triphenylamine-centered dendrimers (<b>CBD-G1</b> and <b>CBD-G2</b>), such that the outer layer is electron-poor and the
inner layer is electron-rich. It is remarkable that the HOMO level
of the NPC dendrimers is as high as −5.17 eV and triplet energy
level is kept above 2.85 eV. These levels of HOMO and triplet energy,
together with good thermal stability and compatibility of solution
processing, make NPC dendrimers ideal host materials for blue triplet
emitters. Using <b>CBD-G2</b> as the host material, the FIrpic-doped
solution-processed light-emitting diodes were fabricated, and maximum
luminous efficiency could be achieved at a record high of 24.7 cd/A
at 484 cd/m<sup>2</sup>
1,3,4-Oxadiazole Containing Silanes as Novel Hosts for Blue Phosphorescent Organic Light Emitting Diodes
Five rigid oxadiazole (OXD) containing silanes, denoted <b>1</b>–<b>5</b>, have been developed with high morphological stability. Disruption of the π-aromatic conjugation by introduction of Si atoms leads to a large band gap and high triplet energy. Among the OXDs we studied, 2,5-bis(triphenylsilylphenyl)-1,3,4-oxadiazole <b>5</b> is the best host for FIrpic, with a phosphorescent organic light emitting diode (PHOLED) turn-on voltage of 6.9 V, maximum luminance of 5124 cd/m<sup>2</sup>, current efficiency of 39.9 cd/A, and external quantum efficiency of 13.1%. Special molecular stacking in the single crystal of <b>5</b> was discussed
Novel Ambipolar Orthogonal Donor–Acceptor Host for Blue Organic Light Emitting Diodes
Ambipolar triplet hosts comprising 1,2,4-triazole and carbazole in ortho-positions have been developed. The blue PHOLED has a high current efficiency of 47.1 cd A<sup>–1</sup>, power efficiency of 41.2 lm W<sup>–1</sup>, and low efficiency roll-off. The high efficiency was attributed to the successful control of π-conjugation through orthogonal arrangement of the substituents so that a wide T<sub>1</sub>–S<sub>0</sub> gap could be maintained
Novel Ambipolar Orthogonal Donor–Acceptor Host for Blue Organic Light Emitting Diodes
Ambipolar triplet hosts comprising 1,2,4-triazole and carbazole in ortho-positions have been developed. The blue PHOLED has a high current efficiency of 47.1 cd A<sup>–1</sup>, power efficiency of 41.2 lm W<sup>–1</sup>, and low efficiency roll-off. The high efficiency was attributed to the successful control of π-conjugation through orthogonal arrangement of the substituents so that a wide T<sub>1</sub>–S<sub>0</sub> gap could be maintained
Novel Ambipolar Orthogonal Donor–Acceptor Host for Blue Organic Light Emitting Diodes
Ambipolar triplet hosts comprising 1,2,4-triazole and carbazole in ortho-positions have been developed. The blue PHOLED has a high current efficiency of 47.1 cd A<sup>–1</sup>, power efficiency of 41.2 lm W<sup>–1</sup>, and low efficiency roll-off. The high efficiency was attributed to the successful control of π-conjugation through orthogonal arrangement of the substituents so that a wide T<sub>1</sub>–S<sub>0</sub> gap could be maintained
Orthogonally Substituted Benzimidazole-Carbazole Benzene As Universal Hosts for Phosphorescent Organic Light-Emitting Diodes
The
novel ambipolar hosts of <i><b>o</b></i><b>-CbzBz</b> and <i><b>o</b></i><b>-DiCbzBz</b> contain
carbazole and benzimidazole through an <i>ortho</i>-connection.
The orthogonal conformations cause the triplet state
to be confined at the carbazole units to secure efficient energy transfer.
The phosphorescent organic light-emitting diodes (PhOLEDs) show a
high current efficiency, power efficiency, and low efficiency roll-off. <i><b>o</b></i><b>-DiCbzBz</b> can be used as a host
for sky-blue, green, and orange-red PhOLEDs, giving 57.5, 78.4, and
60.3 cd/A, respectively
High <i>K</i> Nanophase Zinc Oxide on Biomimetic Silicon Nanotip Array as Supercapacitors
A 3D trenched-structure metal–insulator–metal
(MIM)
nanocapacitor array with an ultrahigh equivalent planar capacitance
(EPC) of ∼300 μF cm<sup>–2</sup> is demonstrated.
Zinc oxide (ZnO) and aluminum oxide (Al<sub>2</sub>O<sub>3</sub>)
bilayer dielectric is deposited on 1 μm high biomimetic silicon
nanotip (SiNT) substrate using the atomic layer deposition method.
The large EPC is achieved by utilizing the large surface area of the
densely packed SiNT (∼5 × 10<sup>10</sup> cm<sup>–2</sup>) coated conformally with an ultrahigh dielectric constant of ZnO.
The EPC value is 30 times higher than those previously reported in
metal–insulator–metal or metal–insulator–semiconductor
nanocapacitors using similar porosity dimensions of the support materials
The Effects of Fluorine-Contained Molecules on Improving the Polymer Solar Cell by Curing the Anomalous S‑Shaped <i>I</i>–<i>V</i> Curve
In this study, we investigate the
effects of fluorinated polyÂ(3,4-ethylene dioxythiophene):polyÂ(styrenesulfonate)
buffer layer on the performance of polymer photovoltaic cells. We
demonstrate for the first time, the deterioration of the device performance
can be effectively mended by modifying the interface between the active
layer and buffer layer with heptadecafluoro-1,1,2,2-tetra-hydro-decyl
trimethoxysilane (PFDS) and perfluorononane. Device performance shows
a substantial enhancement of short-circuit current from 7.90 to 9.39
mA/cm<sup>2</sup> and fill factor from 27% to 53%. The overall device
efficiency was improved from 0.98% to 3.12% for PFDS modified device.
The mechanism of S-shape curing is also discussed. In addition, the
stability of modified devices shows significant improvement than those
without modification. The efficiency of the modified devices retains
about half (1.88%) of its initial efficiency (4.1%) after 30 d compared
to the unmodified ones (0.61%), under air atmosphere