17 research outputs found
Enhanced Light Extraction from p‑Si Nanowires/n-IGZO Heterojunction LED by Using Oxide–Metal–Oxide Structured Transparent Electrodes
Heterojunction
light-emitting diodes (LEDs) comprising p-type Si
nanowires (p-Si NWs) and n-type indium gallium zinc oxide (n-IGZO)
were fabricated with the different top electrode materials: Al, indium
zinc oxide (IZO), and IZO/Ag/IZO oxide–metal–oxide (OMO)
multilayer. All the LEDs exhibited typical rectifying behaviors of
the p–n junction. Moreover, broad light-emission spectra in
the visible range were observed because of the quantum confinement
effect (QCE) of the Si NW and Si nanocrystals/nonstoichiometric Si
oxide (SiO<sub><i>x</i></sub>) (<i>x</i> <
2) interfaces. In comparison to the LEDs with Al and single IZO electrode,
the LED with the OMO multilayer electrode exhibited an enhanced optical
performance because the OMO multilayer had an excellent transmittance
of 87.7% in the visible range with a low sheet resistance of 5.65
Ω/sq. Furthermore, by investigating the transmittance spectra
of the single IZO and OMO multilayer electrodes as a function of the
light incidence angle, the OMO multilayer electrode is confirmed to
be more suitable for white light emission from p-Si NWs/n-IGZO heterojunction
LED
Effect of Nonionic Surfactant Additive in PEDOT:PSS on PFO Emission Layer in Organic–Inorganic Hybrid Light-Emitting Diode
PolyÂ(9,9-dioctylfluorene)
(PFO) has attracted significant interests owing to its versatility
in electronic devices. However, changes in its optical properties
caused by its various phases and the formation of oxidation defects
limit the application of PFO in light-emitting diodes (LEDs). We investigated
the effects of the addition of Triton X-100 (hereinafter shortened
as TX) in polyÂ(3,4-ethylenedioxythiophene):polyÂ(styrenesulfonate)
(PEDOT:PSS) to induce interlayer diffusion between PEDOT:PSS and PFO
to enhance the stability of the PFO phase and suppress its oxidation.
Photoluminescence (PL) measurement on PFO/TX-mixed PEDOT:PSS layers
revealed that, upon increasing the concentration of TX in the PEDOT:PSS
layer, the β phase of PFO could be suppressed in favor of the
glassy phase and the wide PL emission centered at 535 nm caused by
ketone defects formed by oxidation was decreased considerably. LEDs
were then fabricated using PFO as an emission layer, TX-mixed PEDOT:PSS
as hole-transport layer, and zinc oxide (ZnO) nanorods as electron-transport
layer. As the TX concentration reached 3 wt %, the devices exhibited
dramatic increases in current densities, which were attributed to
the enhanced hole injection due to TX addition, along with a shift
in the dominant emission wavelength from a green electroluminescence
(EL) emission centered at 518 nm to a blue EL emission centered at
448 nm. The addition of TX in PEDOT:PSS induced a better hole injection
in the PFO layer, and through interlayer diffusion, stabilized the
glassy phase of PFO and limited the formation of oxidation defects
Micropatternable Double-Faced ZnO Nanoflowers for Flexible Gas Sensor
Micropatternable
double-faced (DF) zinc oxide (ZnO) nanoflowers (NFs) for flexible
gas sensors have been successfully fabricated on a polyimide (PI)
substrate with single-walled carbon nanotubes (SWCNTs) as electrode.
The fabricated sensor comprises ZnO nanoshells laid out on a PI substrate
at regular intervals, on which ZnO nanorods (NRs) were grown in- and
outside the shells to maximize the surface area and form a connected
network. This three-dimensional network structure possesses multiple
gas diffusion channels and the micropatterned island structure allows
the stability of the flexible devices to be enhanced by dispersing
the strain into the empty spaces of the substrate. Moreover, the micropatterning
technique on a flexible substrate enables highly integrated nanodevices
to be fabricated. The SWCNTs were chosen as the electrode for their
flexibility and the Schottky barrier they form with ZnO, improving
the sensing performance. The devices exhibited high selectivity toward
NO<sub>2</sub> as well as outstanding sensing characteristics with
a stable response of 218.1, fast rising and decay times of 25.0 and
14.1 s, respectively, and percent recovery greater than 98% upon NO<sub>2</sub> exposure. The superior sensing properties arose from a combination
of high surface area, numerous active junction points, donor point
defects in the ZnO NRs, and the use of the SWCNT electrode. Furthermore,
the DF-ZnO NF gas sensor showed sustainable mechanical stability.
Despite the physical degradation observed, the devices still demonstrated
outstanding sensing characteristics after 10 000 bending cycles
at a curvature radius of 5 mm
Highly Scalable Synthesis of MoS<sub>2</sub> Thin Films with Precise Thickness Control via Polymer-Assisted Deposition
Highly Scalable Synthesis of MoS<sub>2</sub> Thin
Films with Precise Thickness Control via Polymer-Assisted Depositio
High-Performance Green Light-Emitting Diodes Based on MAPbBr<sub>3</sub>–Polymer Composite Films Prepared by Gas-Assisted Crystallization
The
morphology of perovskite films has a significant impact on luminous
characteristics of perovskite light-emitting diodes (PeLEDs). To obtain
a highly uniform methylammonium lead tribromide (MAPbBr<sub>3</sub>) film, a gas-assisted crystallization method is introduced with
a mixed solution of MAPbBr<sub>3</sub> precursor and polymer matrix.
The ultrafast evaporation of the solvent causes a high degree of supersaturation
which expedites the generation of a large number of nuclei to form
a MAPbBr<sub>3</sub>–polymer composite film with full surface
coverage and nano-sized grains. The addition of the polymer matrix
significantly affects the optical properties and morphology of MAPbBr<sub>3</sub> films. The PeLED made of the MAPbBr<sub>3</sub>–polymer
composite film exhibits an outstanding device performance of a maximum
luminance of 6800 cd·m<sup>–2</sup> and a maximum current
efficiency of 1.12 cd·A<sup>–1</sup>. Furthermore, 1 cm<sup>2</sup> area pixel of PeLED displays full coverage of a strong green
electroluminescence, implying that the high-quality perovskite film
can be useful for large-area applications in perovskite-based optoelectronic
devices
Low-Temperature Facile Synthesis of Sb-Doped p‑Type ZnO Nanodisks and Its Application in Homojunction Light-Emitting Diode
This
study explores low-temperature solution-process-based seed-layer-free
ZnO p–n homojunction light-emitting diode (LED). In order to
obtain p-type ZnO nanodisks (NDs), antimony (Sb) was doped into ZnO
by using a facile chemical route at 120 °C. The X-ray photoelectron
spectra indicated the presence of (Sb<sub>Zn</sub>–2V<sub>Zn</sub>) acceptor complex in the Sb-doped ZnO NDs. Using these NDs as freestanding
templates, undoped n-type ZnO nanorods (NRs) were epitaxially grown
at 95 °C to form ZnO p–n homojunction. The homojunction
with a turn-on voltage of 2.5 V was found to be significantly stable
up to 100 s under a constant voltage stress of 5 V. A strong orange-red
emission was observed by the naked eye under a forward bias of 5 V.
The electroluminescence spectra revealed three major peaks at 400,
612, and 742 nm which were attributed to the transitions from Zn<sub>i</sub> to VBM, from Zn<sub>i</sub> to O<sub>i</sub>, and from V<sub>O</sub> to VBM, respectively. The presence of these deep-level defects
was confirmed by the photoluminescence of ZnO NRs. This study paves
the way for future applications of ZnO homojunction LEDs using low-temperature
and low-cost solution processes with the controlled use of native
defects
Self-Seeded Growth of Poly(3-hexylthiophene) (P3HT) Nanofibrils by a Cycle of Cooling and Heating in Solutions
In spite of the recent successes in transistors and solar
cells
utilizing polyÂ(3-hexylthiophene) (P3HT) nanofibrils, systematic analysis
on the growth kinetics has not been reported due to the lack of analytical
tools. This study proposed a simple spectroscopic method to obtain
the crystallinity of P3HT in solutions. On the basis of the analytical
approach, we found that the crystallinity hysteresis upon temperature
is a simple function of the solubility parameter difference (Δδ)
between the P3HT and the solvents. When Δδ ≥ 0.7,
a cooling (−20 °C)-and-heating (25 °C) process allowed
the preparation of solutions including 1D crystal seeds dispersed
in the solution. Simple coating of the seeded solutions completed
the growth of the seeds into long nanofibrils at the early stage of
the coating and thereby achieved almost 100% crystallinity in the
resulting films without any postannealing process. The existence of
PCBM for bulk-heterojunction (BHJ) solar cells did not affect the
nucleation and growth of the nanofibrils during the cooling-and-heating
process. The solar cells prepared from the solutions with Δδ
≥ 0.7 had solar conversion efficiencies higher than the conventional
thermally annealed cells
Assembled Monolayers of Hydrophilic Particles on Water Surfaces
A facile and quick approach to prepare self-assembled monolayers of water-dispersible particles on the water surface is presented. Particle suspensions in alcohols were dropped on a water reservoir to form long-range ordered monolayers of various particles, including spherical solid particles, soft hydrogel particles, metal nanoparticles, quantum dots, nanowires, single-wall carbon nanotubes (SWCNTs), nanoplates, and nanosheets. A systematic study was conducted on the variables affecting the monolayer assembly: the solubility parameter of spreading solvents, particle concentration, zeta potential of the particles in the suspension, surface tension of the water phase, hardness of the particles, and addition of a salt in the suspension. This method requires no hydrophobic surface treatment of the particles, which is useful to exploit these monolayer films without changing the native properties of the particles. The study highlights a quick 2D colloidal assembly without cracks in the wafer scale as well as transparent conductive thin films made of SWCNTs and graphenes
Assembled Monolayers of Hydrophilic Particles on Water Surfaces
A facile and quick approach to prepare self-assembled monolayers of water-dispersible particles on the water surface is presented. Particle suspensions in alcohols were dropped on a water reservoir to form long-range ordered monolayers of various particles, including spherical solid particles, soft hydrogel particles, metal nanoparticles, quantum dots, nanowires, single-wall carbon nanotubes (SWCNTs), nanoplates, and nanosheets. A systematic study was conducted on the variables affecting the monolayer assembly: the solubility parameter of spreading solvents, particle concentration, zeta potential of the particles in the suspension, surface tension of the water phase, hardness of the particles, and addition of a salt in the suspension. This method requires no hydrophobic surface treatment of the particles, which is useful to exploit these monolayer films without changing the native properties of the particles. The study highlights a quick 2D colloidal assembly without cracks in the wafer scale as well as transparent conductive thin films made of SWCNTs and graphenes
Adopting Novel Strategies in Achieving High-Performance Single-Layer Network Structured ZnO Nanorods Thin Film Transistors
High-performance,
solution-processed transparent and flexible zinc oxide (ZnO) nanorods
(NRs)-based single layer network structured thin film transistors
(TFTs) were developed on polyethylene terephthalate (PET) substrate
at 100 °C. Keeping the process-temperature under 100 °C,
we have improved the device performance by introducing three low temperature-based
techniques; regrowing ZnO to fill the void spaces in a single layer
network of ZnO NRs, passivating the back channel with polymer, and
adopting ZrO<sub>2</sub> as the high-<i>k</i> dielectric.
Notably, high-<i>k</i> amorphous ZrO<sub>2</sub> was synthesized
and deposited using a novel method at an unprecedented temperature
of 100 °C. Using these methods, the TFTs exhibited a high mobility
of 1.77 cm<sup>2</sup>/V·s. An insignificant reduction of 2.18%
in mobility value after 3000 cycles of dynamic bending at a radius
of curvature of 20 mm indicated the robust mechanical nature of the
flexible ZnO NRs SLNS TFTs