10 research outputs found
Fabrication of Intrinsic, Elastic, Self-healing, and Luminescent CsPbBr<sub>3</sub> Quantum Dot-Polymer Composites via ThiolâEne Cross-Linking
Here, we offer a straightforward approach for making
elastic, self-healing,
and light-conversion material, in which CsPbBr3 quantum
dots (QDs) form a strong bond with a designed copolymer including
elastic behavior based on the mechanical characteristics of polyisoprene
and reversible bonding moieties for self-healing function. This designed
composite film has highly luminescent and typically elastic properties,
including good ultimate strength (âź0.14 N/mm2) and
high stretchability (âź486%). The copolymer matrix exhibited
excellent compatibility with CsPbBr3 QDs, in which they
maintained their uniform distribution within the network after a serial
stretching process due to the strong bond between copolymers and CsPbBr3 QDs. Furthermore, the composite film dynamic network is capable
of 90% self-healing efficiency at room temperature without the need
of any healing stimulus, heat, plasticizer, or solvent. This simple
method suggested a relatively easy approach to a stable, elastic,
and luminescent CsPbBr3 QD-based composite film that opens
up the potential of fully stretchable light conversion material for
light-emitting diodes
Fabrication of Intrinsic, Elastic, Self-healing, and Luminescent CsPbBr<sub>3</sub> Quantum Dot-Polymer Composites via ThiolâEne Cross-Linking
Here, we offer a straightforward approach for making
elastic, self-healing,
and light-conversion material, in which CsPbBr3 quantum
dots (QDs) form a strong bond with a designed copolymer including
elastic behavior based on the mechanical characteristics of polyisoprene
and reversible bonding moieties for self-healing function. This designed
composite film has highly luminescent and typically elastic properties,
including good ultimate strength (âź0.14 N/mm2) and
high stretchability (âź486%). The copolymer matrix exhibited
excellent compatibility with CsPbBr3 QDs, in which they
maintained their uniform distribution within the network after a serial
stretching process due to the strong bond between copolymers and CsPbBr3 QDs. Furthermore, the composite film dynamic network is capable
of 90% self-healing efficiency at room temperature without the need
of any healing stimulus, heat, plasticizer, or solvent. This simple
method suggested a relatively easy approach to a stable, elastic,
and luminescent CsPbBr3 QD-based composite film that opens
up the potential of fully stretchable light conversion material for
light-emitting diodes
Synthesis, Morphology, and Sensory Applications of Multifunctional RodâCoilâCoil Triblock Copolymers and Their Electrospun Nanofibers
We report the synthesis, morphology, and applications
of conjugated
rodâcoilâcoil triblock copolymers, polyfluorene<i>-block-</i>polyÂ(<i>N</i>-isopropylacrylamide)<i>-block</i>-polyÂ(N-methylolacrylamide) (<b>PF</b><b>-</b><i><b>b</b></i><b>-</b><b>PNIPAAm</b><i><b>-b-</b></i><b>PNMA</b>), prepared by
atom transfer radical polymerization first and followed by click coupling
reaction. The blocks of PF, PNIPAAm, and PNMA were designed for fluorescent
probing, hydrophilic thermo-responsive and chemically cross-linking,
respectively. In the following, the electrospun (ES) nanofibers of
PF-<i>b</i>-PNIPAAm-<i>b</i>-PNMA were prepared
in pure water using a single-capillary spinneret. The SAXS and TEM
results suggested the lamellar structure of the <b>PF</b><b>-</b><i><b>b</b></i><b>-</b><b>PNIPAAm</b><b>-</b><i><b>b</b></i><b>-</b><b>PNMA</b> along the fiber axis. These obtained nanofibers showed
outstanding wettability and dimension stability in the aqueous solution,
and resulted in a reversible on/off transition on photoluminescence
as the temperatures varied. Furthermore, the high surface/volume ratio
of the ES nanofibers efficiently enhanced the temperature-sensitivity
and responsive speed compared to those of the drop-cast film. The
results indicated that the ES nanofibers of the conjugated rodâcoil
block copolymers would have potential applications for multifunctional
sensory devices
Fabrication of Intrinsic, Elastic, Self-healing, and Luminescent CsPbBr<sub>3</sub> Quantum Dot-Polymer Composites via ThiolâEne Cross-Linking
Here, we offer a straightforward approach for making
elastic, self-healing,
and light-conversion material, in which CsPbBr3 quantum
dots (QDs) form a strong bond with a designed copolymer including
elastic behavior based on the mechanical characteristics of polyisoprene
and reversible bonding moieties for self-healing function. This designed
composite film has highly luminescent and typically elastic properties,
including good ultimate strength (âź0.14 N/mm2) and
high stretchability (âź486%). The copolymer matrix exhibited
excellent compatibility with CsPbBr3 QDs, in which they
maintained their uniform distribution within the network after a serial
stretching process due to the strong bond between copolymers and CsPbBr3 QDs. Furthermore, the composite film dynamic network is capable
of 90% self-healing efficiency at room temperature without the need
of any healing stimulus, heat, plasticizer, or solvent. This simple
method suggested a relatively easy approach to a stable, elastic,
and luminescent CsPbBr3 QD-based composite film that opens
up the potential of fully stretchable light conversion material for
light-emitting diodes
High-Performance Nonvolatile Organic Transistor Memory Devices Using the Electrets of Semiconducting Blends
Organic nonvolatile transistor memory
devices of the <i>n</i>-type semiconductor <i>N</i>,<i>N</i>â˛-bisÂ(2-phenylethyl)-perylene-3,4:9,10-tetracarboxylic
diimide (BPE-PTCDI) were prepared using various electrets (i.e., three-armed
star-shaped polyÂ[4-(diphenylamino)Âbenzyl methacrylate] (NÂ(PTPMA)<sub>3</sub>) and its blends with 6,6-phenyl-C<sub>61</sub>-butyric acid
methyl ester (PCBM), 6,13-bisÂ(triisopropylsilylethynyl)Âpentacene (TIPS-pen)
or ferrocene). In the device using the PCBM:NÂ(PTPMA)<sub>3</sub> blend
electret,
it changed its memory feature from a write-once-read-many (WORM) type
to a flash type as the PCBM content increased and could be operated
repeatedly based on a tunneling process. The large shifts on the reversible
transfer curves and the hysteresis after implementing a gate bias
indicated the considerable charge storage in the electret layer. On
the other hand, the memory characteristics showed a flash type and
a WORM characteristic, respectively, using the donor/donor electrets
TIPS-pen:NÂ(PTPMA)<sub>3</sub> and ferrocene:NÂ(PTPMA)<sub>3</sub>.
The variation on the memory characteristics was attributed to the
difference of energy barrier at the interface when different types
of electret materials were employed. All the studied memory devices
exhibited a long retention over 10<sup>4</sup> s with a highly stable
read-out current. In addition, the afore-discussed memory devices
by inserting another electret layer of polyÂ(methacrylic acid) (PMAA)
between the BPE-PTCDI layer and the semiconducting blend layer enhanced
the write-read-erase-read (WRER) operation cycle as high as 200 times.
This study suggested that the energy level and charge transfer in
the blend electret had a significant effect on tuning the characteristics
of nonvolatile transistor memory devices
Using a Single Electrospun Polymer Nanofiber to Enhance Carrier Mobility in Organic Field-Effect Transistors toward Nonvolatile Memory
In
this work, a single electrospun polymer nanofiber was employed
as an additional dielectric in organic field-effect transistors where
the active channel was a layer of pentacene. A high field-effect mobility
(>1.50 cm<sup>2</sup>/(V¡s)) and a high ON/OFF current ratio
(>10<sup>6</sup>) could be achieved by the use of such a nanofiber.
Probing by electron microscopy, atomic force microscopy, and scattering
techniques, we found that the geometry of the fiber is key to induce
a pentacene morphology with large and oriented grains that facilitates
the charge transport in pentacene layer along the fiber. The feasibility
of nonvolatile memory based on this new type of transistor has been
explored and the devices showed a fairly high memory window and reliable
memory characteristics. In addition to pure polymers, the effects
of composite nanofibers with dispersed [6,6]-phenyl-C<sub>61</sub>-butyric acid methyl ester were also investigated, and the electrical
properties and memory characteristics of the transistors were found
to be further improved. This study highlights the importance of dielectric
geometry to pentacene morphology that is decisive for the performances
of organic field-effect transistors
Synthesis of Oligosaccharide-Based Block Copolymers with Pendent ĎâConjugated Oligofluorene Moieties and Their Electrical Device Applications
We report the synthesis and electric
device applications of oligosaccharide-based
diblock copolymers consisting of a maltoheptaose (MH) block and a
polyÂ(4-oligofluorenylÂstyrene) block (PStFl<sub><i>n</i></sub>, <i>n</i> = 1 or 2), referred to as MH-<i>b</i>-PStFl<sub><i>n</i></sub>. MH-<i>b</i>-PStFl<sub><i>n</i></sub> was prepared by the CuÂ(I)-catalyzed click
reaction of azido-terminated PStFl<sub><i>n</i></sub> (PStFl<sub><i>n</i></sub>-N<sub>3</sub>), which was obtained from
the azidation reaction of the bromo-terminated PStFl<sub><i>n</i></sub> (PStFl<sub><i>n</i></sub>-Br), with excess ethynyl-terminated
MH in the THF/DMF mixture solvent. The resulting diblock copolymers
self-assembled to spherical microdomains with sub-10 nm sizes in both
bulk and thin film state after annealing process. Thereafter, the
MH-<i>b</i>-PStFl<sub><i>n</i></sub> thin film
(âź50 nm) with the self-assembled nanoscale spherical aggregates
was used as the charge storage layer for the pentacene-based field-effect
transistor type memory devices. The MH-<i>b</i>-PStFl<sub><i>n</i></sub>-based devices had the excellent hole mobility
(0.25â0.52 cm<sup>2</sup> V<sup>â1</sup> s<sup>â1</sup>) and the high ON/OFF current (<i>I</i><sub>ON</sub>/<i>I</i><sub>OFF</sub>) ratio of 10<sup>7</sup>â10<sup>8</sup>, of which the MH-<i>b</i>-PStFl<sub>1</sub>-based one
had the higher mobility than that of the MH-<i>b</i>-PStFl<sub>2</sub>-based one because the pentacene crystal in the former device
possessed the larger grain size and fewer boundaries. On the other
hand, the MH-<i>b</i>-PStFl<sub>2</sub>-based device showed
a larger memory window than the MH-<i>b</i>-PStFl<sub>1</sub>-based one because the stronger electron-donating effect of the difluorenyl
group in MH-<i>b</i>-PStFl<sub>2</sub> increased the charge
storage capability of its related device. All the memory devices showed
a long-term retention time over 10<sup>4</sup> s with the high <i>I</i><sub>ON</sub>/<i>I</i><sub>OFF</sub> ratio of
10<sup>6</sup>â10<sup>8</sup>. Among these devices, the MH-<i>b</i>-PStFl<sub>1</sub>-based device showed a good WRER endurance
over 180 cycles. This work not only demonstrates the tunable electrical
memory characteristics by adjusting the Ď-conjugation length
of the oligofluorenyl side chain in the polymer electret but also
provides a promising approach for developing the next-generation âgreen
electronicsâ using natural materials
Partially-Screened Field Effect and Selective Carrier Injection at Organic Semiconductor/Graphene Heterointerface
Due
to the lack of a bandgap, applications of graphene require special
device structures and engineering strategies to enable semiconducting
characteristics at room temperature. To this end, graphene-based vertical
field-effect transistors (VFETs) are emerging as one of the most promising
candidates. Previous work attributed the current modulation primarily
to gate-modulated grapheneâsemiconductor Schottky barrier.
Here, we report the first experimental evidence that the partially
screened field effect and selective carrier injection through graphene
dominate the electronic transport at the organic semiconductor/graphene
heterointerface. The new mechanistic insight allows us to rationally
design graphene VFETs. Flexible organic/graphene VFETs with bending
radius <1 mm and the output current per unit layout area equivalent
to that of the best oxide planar FETs can be achieved. We suggest
driving organic light emitting diodes with such VFETs as a promising
application
Ultrapure Green Light-Emitting Diodes Using Two-Dimensional Formamidinium Perovskites: Achieving Recommendation 2020 Color Coordinates
Pure
green light-emitting diodes (LEDs) are essential for realizing
an ultrawide color gamut in next-generation displays, as is defined
by the recommendation (Rec.) 2020 standard. However, because the human
eye is more sensitive to the green spectral region, it is not yet
possible to achieve an ultrapure green electroluminescence (EL) with
a sufficiently narrow bandwidth that covers >95% of the Rec. 2020
standard in the CIE 1931 color space. Here, we demonstrate efficient,
ultrapure green EL based on the colloidal two-dimensional (2D) formamidinium
lead bromide (FAPbBr<sub>3</sub>) hybrid perovskites. Through the
dielectric quantum well (DQW) engineering, the quantum-confined 2D
FAPbBr<sub>3</sub> perovskites exhibit a high exciton binding energy
of 162 meV, resulting in a high photoluminescence quantum yield (PLQY)
of âź92% in the spin-coated films. Our optimized LED devices
show a maximum current efficiency (Ρ<sub>CE</sub>) of 13.02
cd A<sup>â1</sup> and the CIE 1931 color coordinates of (0.168,
0.773). The color gamut covers 97% and 99% of the Rec. 2020 standard
in the CIE 1931 and the CIE 1976 color space, respectively, representing
the âgreenestâ LEDs ever reported. Moreover, the device
shows only a âź10% roll-off in Ρ<sub>CE</sub> (11.3 cd
A<sup>â1</sup>) at 1000 cd m<sup>â2</sup>. We further
demonstrate large-area (3 cm<sup>2</sup>) and ultraflexible (bending
radius of 2 mm) LEDs based on 2D perovskites
Stretchable Self-Healing Polymeric Dielectrics Cross-Linked Through MetalâLigand Coordination
A self-healing dielectric elastomer
is achieved by the incorporation
of metalâligand coordination as cross-linking sites in nonpolar
polydimethylsiloxane (PDMS) polymers. The ligand is 2,2â˛-bipyridine-5,5â˛-dicarboxylic
amide, while the metal salts investigated here are Fe<sup>2+</sup> and Zn<sup>2+</sup> with various counteranions. The kinetically
labile coordination between Zn<sup>2+</sup> and bipyridine endows
the polymer fast self-healing ability at ambient condition. When integrated
into organic field-effect transistors (OFETs) as gate dielectrics,
transistors with FeCl<sub>2</sub> and ZnCl<sub>2</sub> salts cross-linked
PDMS exhibited increased dielectric constants compared to PDMS and
demonstrated hysteresis-free transfer characteristics, owing to the
low ion conductivity in PDMS and the strong columbic interaction between
metal cations and the small Cl<sup>â</sup> anions which can
prevent mobile anions drifting under gate bias. Fully stretchable
transistors with FeCl<sub>2</sub>-PDMS dielectrics were fabricated
and exhibited ideal transfer characteristics. The gate leakage current
remained low even after 1000 cycles at 100% strain. The mechanical
robustness and stable electrical performance proved its suitability
for applications in stretchable electronics. On the other hand, transistors
with gate dielectrics containing large-sized anions (BF<sub>4</sub><sup>â</sup>, ClO<sub>4</sub><sup>â</sup>, CF<sub>3</sub>SO<sub>3</sub><sup>â</sup>) displayed prominent hysteresis
due to mobile anions drifting under gate bias voltage. This work provides
insights on future design of self-healing stretchable dielectric materials
based on metalâligand cross-linked polymers