15 research outputs found
Luminescence enhancement by symmetry-breaking in the excited state in radical organic light-emitting diodes
Organic π-conjugated radicals have recently joined the ranks of high-efficiency light-emitting materials; however, their light-emission mechanism is still a matter of debate. Here, the authors highlight a recently proposed luminescent enhancement mechanism and record-breaking efficiency of a radical organic light-emitting diode
Interfacial Engineering of Perovskite Quantum-Dot Light-Emitting Devices Using Alkyl Ammonium Salt Layer
Efficient Electron Injection by Size- and Shape-Controlled Zinc Oxide Nanoparticles in Organic Light-Emitting Devices
Two-Dimensional Ca<sub>2</sub>Nb<sub>3</sub>O<sub>10</sub> Perovskite Nanosheets for Electron Injection Layers in Organic Light-Emitting Devices
We report in this
article the application of calcium niobate (CNO)
perovskite nanosheets for electron injection layers (EILs) in organic
light-emitting devices (OLEDs). Four kinds of tetraalkylammonium hydroxides
having different alkyl lengths were utilized as the exfoliation agents
of a layered compound precursor HCa<sub>2</sub>Nb<sub>3</sub>O<sub>10</sub> to synthesize CNO nanosheets, including tetramethylammonium
hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide
(TPAOH), and tetrabutylammonium hydroxide. CNO nanosheet EILs were
applied in fluorescent poly[(9,9-di-<i>n</i>-octylfluorenyl-2,7-diyl)-<i>alt</i>-(benzo[2,1,3]thiadiazol-4,8-diyl)] (F8BT) organic light-emitting
polymer-based devices. The effects of dispersion concentrations and
alkyl chain length on the devices’ performances were investigated.
The results demonstrated that OLEDs’ performances were related
to the coverage ratio of the CNO nanosheets, their thicknesses, and
their work function values. Among the four exfoliation agents, the
device with CNO nanosheets exfoliated by TPAOH showed the lowest driving
voltage. The OLEDs with the CNO nanosheet EILs showed lower driving
voltages compared with the devices with conventional EIL material
lithium 8-quinolate
A Solution-Processed Heteropoly Acid Containing MoO<sub>3</sub> Units as a Hole-Injection Material for Highly Stable Organic Light-Emitting Devices
We report hole-injection
layers (HILs) comprising a heteropoly acid containing MoO<sub>3</sub> units, phosphomolybdic acid (PMA), in organic light-emitting devices
(OLEDs). PMA possesses outstanding properties, such as high solubility
in organic solvents, very low surface roughness in the film state,
high transparency in the visible region, and an appropriate work function
(WF), that make it suitable for HILs. We also found that these properties
were dependent on the postbaking atmosphere and temperature after
film formation. When the PMA film was baked in N<sub>2</sub>, the
Mo in the PMA was reduced to Mo(V), whereas baking in air had no influence
on the Mo valence state. Consequently, different baking atmospheres
yielded different WF values. OLEDs with PMA HILs were fabricated and
evaluated. OLEDs with PMA baked under appropriate conditions exhibited
comparably low driving voltages and higher driving stability compared
with OLEDs employing conventional hole-injection materials (HIMs),
poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate),
and evaporated MoO<sub>3</sub>, which clearly shows the high suitability
of PMA HILs for OLEDs. PMA is also a commercially available and very
cheap material, leading to the widespread use of PMA as a standard
HIM
Colorful Squaraines Dyes for Efficient Solution-Processed All Small-Molecule Semitransparent Organic Solar Cells
Molecular Interdiffusion between Stacked Layers by Solution and Thermal Annealing Processes in Organic Light Emitting Devices
Molecular Interdiffusion between Stacked Layers by Solution and Thermal Annealing Processes in Organic Light Emitting Devices
In
organic light emitting devices (OLEDs), interfacial structures
between multilayers have large impacts on the characteristics of OLEDs.
Herein, we succeeded in revealing the interdiffusion in solution processed
and thermal annealed OLEDs by neutron reflectometry. We investigated
interfaces between a polymer under layer and small molecules upper
layer. The small molecules diffused into the swollen polymer layer
during the interfacial formation by the solution process, but the
polymer did not diffuse into the small molecules layer. At temperatures
close to the glass transition temperatures of the materials, asymmetric
molecular diffusion was observed. We elucidated the effects of the
interdiffusion on the characteristics of OLEDs. Partially mixing the
interface improved the current efficiencies due to suppressed triplet-polaron
quenching at the interface. Controlling and understanding the interfacial
structures of the miultilayers will be more important to improve the
OLED characteristics
Efficient Electron Injection by Size- and Shape-Controlled Zinc Oxide Nanoparticles in Organic Light-Emitting Devices
Three
different sized zinc oxide (ZnO) nanoparticles were synthesized as
spherical ZnO (S-ZnO), rodlike ZnO (R-ZnO), and intermediate shape
and size ZnO (I-ZnO) by controlling the reaction time. The average
sizes of the ZnO nanoparticles were 4.2 nm × 3.4 nm for S-ZnO,
9.8 nm × 4.5 nm for I-ZnO, and 20.6 nm × 6.2 nm for R-ZnO.
Organic light-emitting devices (OLEDs) with these ZnO nanoparticles
as the electron injection layer (EIL) were fabricated. The device
with I-ZnO showed lower driving voltage and higher power efficiency
than those with S-ZnO and R-ZnO. The superiority of I-ZnO makes it
very effective as an EIL for various types of OLEDs regardless of
the deposition order or method of fabricating the organic layer, the
ZnO layer, and the electrode
Colorful Squaraines Dyes for Efficient Solution-Processed All Small-Molecule Semitransparent Organic Solar Cells
Semitransparent organic solar cells
(ST-OSCs) exhibit highly promising
applications to develop integrated photovoltaics and power-generating
windows. However, the development of ST-OSCs is significantly lagging
behind opaque OSCs, especially for all small-molecule ST-OSCs. Here,
four unique squaraines dyes (IDPSQ, SQ-BP, D-BDT-SQ, and AzUSQ) were
successfully used as donors in ST-OSCs, whose colors can be tuned
from purple to blue, green, and dark green, respectively. While using
ultrathin Ag as a transparent electrode, the ST-OSCs fabricated using
IDPSQ:PC<sub>71</sub>BM, SQ-BP:PC<sub>71</sub>BM, D-BDT-SQ:PC<sub>71</sub>BM, and AzUSQ:PC<sub>71</sub>BM yield power conversion efficiencies
(PCEs) of 2.96, 4.36, 4.91, and 1.71%, respectively, and their colors
are purple, cyan, brown, and light brown, respectively. Compared to
their opaque OSCs (PCEs of 3.95, 5.45, 5.84, and 1.91%, respectively),
the reduction in the PCEs are as low as 25, 20, 16, and 10%, respectively.
Furthermore, each of these ST-OSCs exhibit good average visible transmittance
(AVT) of 25–30%, favorable CIE color coordinates, and a color
rendering index (CRI) of 71–97%. Finally, by changing the thickness
of the Ag electrode, an impressive PCE of 4.9% along with an AVT of
25% and a CRI of 97% can be obtained in D-BDT-SQ:PC<sub>71</sub>BM-based
ST-OSCs, which is the highest PCE among all small-molecule ST-OSCs