27 research outputs found
Nonvolatile Organic Thin Film Transistor Memory Devices Based on Hybrid Nanocomposites of Semiconducting Polymers: Gold Nanoparticles
We report the facile fabrication
and characteristics of organic thin film transistor (OTFT)-based nonvolatile
memory devices using the hybrid nanocomposites of semiconducting polyÂ(9,9-dioctylfluorene-alt-bithiophene)
(F8T2) and ligand-capped Au nanoparticles (NPs), thereby serving as
a charge storage medium. Electrical bias sweep/excitation effectively
modulates the current response of hybrid memory devices through the
charge transfer between F8T2 channel and functionalized Au NPs trapping
sites. The electrical performance of the hybrid memory devices can
be effectively controlled though the loading concentrations (0–9
%) of Au NPs and organic thiolate ligands on Au NP surfaces with different
carbon chain lengths (Au-L6, Au-L10, and Au-L18). The memory window
induced by voltage sweep is considerably increased by the high content
of Au NPs or short carbon chain on the ligand. The hybrid nanocomposite
of F8T2:9% Au-L6 provides the OTFT memories with a memory window of
∼41 V operated at ±30 V and memory ratio of ∼1
× 10<sup>3</sup> maintained for 1 × 10<sup>4</sup> s. The
experimental results suggest that the hybrid materials of the functionalized
Au NPs in F8T2 matrix have the potential applications for low voltage-driven
high performance nonvolatile memory devices
Stretchable Polymer Dielectrics for Low-Voltage-Driven Field-Effect Transistors
A stretchable and mechanical robust
field-effect transistor is
essential for soft wearable electronics. To realize stretchable transistors,
elastic dielectrics with small current hysteresis, high elasticity,
and high dielectric constants are the critical factor for low-voltage-driven
devices. Here, we demonstrate the polar elastomer consisting of polyÂ(vinyliÂdene
fluoride-hexaÂfluoroÂpropylene) (PVDF-HFP):​polyÂ(4-vinylÂphenol)
(PVP). Owing to the high dielectric constant of PVDF-HFP, the device
can be operated under less than 5 V and shows a linear-regime hole
mobility as high as 0.199 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> without significant current hysteresis. Specifically,
the PVDF-HFP:​PVP blends induce the vertical phase separation
and significantly reduce current leakage and reduce the crystallization
of PVDF segments, which can contribute current hysteresis in the OFET
characteristics. All-stretchable OFETs based on these PVDF-HFP:​PVP
dielectrics were fabricated. The device can still keep the hole mobility
of approximately 0.1 cm<sup>2</sup>/​(V s) under a low operation
voltage of 3 V even as stretched with 80% strain. Finally, we successfully
fabricate a low-voltage-driven stretchable transistor. The low voltage
operating under strains is the desirable characteristics for soft
and comfortable wearable electronics
Biaxially Extended Conjugated Polymers with Thieno[3,2‑<i>b</i>]thiophene Building Block for High Performance Field-Effect Transistor Applications
Biaxially
thiophene side chain extended thienoÂ[3,2-<i>b</i>]Âthiophene
(TT2T)-based polymers, PTTT2T, P2TTT2T, PTTTT2T, and PTVTTT2T, were
synthesized by Stille coupling polymerization with different conjugated
moieties of thiophene (T), bithiophene (2T), thienoÂ[3,2-<i>b</i>]Âthiophene (TT), and thiophene–vinylene–thiophene (TVT),
respectively. The electronic properties of the prepared polymers could
be effectively tuned because the variant π-conjugated building
block affected the backbone conformation and the resulted morphology.
The morphology of the thin films characterized by atomic force microscopy
and grazing incidence X-ray diffraction showed that P2TTT2T and PTVTTT2T
thin films possessed a better molecular packing with a nanofiber structure
owing to their coplanar backbone. The average field-effect mobilities
of PTTT2T, P2TTT2T, PTTTT2T, and PTVTTT2T were 6.7 × 10<sup>–6</sup>, 0.36, 2.2 × 10<sup>–3</sup>, and 0.64 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> (maximum 0.71), respectively,
attributed to the coplanarity of polymer skeleton. In addition, the
fabricated FET devices showed a high on/off ratio over 10<sup>7</sup> under ambient for over 3 months, suggesting the excellent environmental
stability. The above results demonstrated that the biaxially extended
fused thiophene based conjugated polymers could serve as a potential
candidate for organic electronic device applications
Interplay between the Phase Transitions at Different Length Scales in the Supramolecular Comb–Coil Block Copolymers Bearing (AB)<sub><i>n</i></sub> Multiblock Architecture
We introduced the concept of comb–coil
supramolecule into
linear (AB)<sub><i>n</i></sub>-type multiblock copolymer
and investigated the self-assembly behavior of the copolymers as a
function of the unit number <i>n</i>. Linear (polystyrene-<i>block</i>-polyÂ(2-vinylpyridine))<sub><i>n</i></sub> (denoted as (PS-<i>b</i>-P2VP)<sub><i>n</i></sub>, where <i>n</i> = 1, 2, 3) was complexed with a surfactant,
dodecylbenzenesulfonic acid (DBSA), to yield the comb–coil
multiblock copolymers, in which DBSA bound stoichiometrically with
P2VP block via physical bonds. All three comb–coil block copolymers,
including diblock (<i>n</i> = 1), tetrablock (<i>n</i> = 2), and hexablock (<i>n</i> = 3), self-organized to
form cylinder-<i>within</i>-lamellae morphology at the lower
temperature, where the cylindrical microdomains formed by the PS block
embedded in the matrix composed of the lamellar mesophase organized
by the P2VPÂ(DBSA) comb block. The disordering of the smaller-scale
lamellar mesophase formed by the comb block occurred upon heating;
at the same time, the larger-scale cylindrical domains transformed
to body-centered cubic-packed spheres in the diblock complex and to
another hexagonally packed cylinder structure with smaller domain
spacing in tetrablock and hexablock complexes, indicating that the
order–disorder transition (ODT) of the smaller-scale structure
drove an order–order transition (OOT) of the larger-scale structure
irrespective of <i>n</i>. The transition temperatures were
found to increase with increasing <i>n</i> due to the introduction
of more interfacial area in the microphase-separated state of the
multiblock with larger unit number
Signal intensity of tumor tissue on MCE-MRI.
<p>(A) Signal intensity and (B) relative signal enhancement in the endometrial and cervical cancer prior to (time = 0 s) and after contrast administration. * = p < 0.05, ** = p < 0.01 by unpaired t-test. Data are expressed as mean ± SEM. Abbreviations: SI, signal intensity; SI<sub>0</sub>, pre-contrast SI<sub>t</sub>; SI following contrast administration; SI<sub>relative</sub>, relative signal enhancement.</p
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>′-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
Synthesis, Morphology, and Field-Effect Transistor Characteristics of Crystalline Diblock Copolymers Consisted of Poly(3-hexylthiophene) and Syndiotactic Polypropylene
We
report the synthesis, morphology, and the field effect transistor
(FET) characteristics of the crystalline diblock copolymers of polyÂ(3-hexylthiophene)
and syndiotactic polypropylene (P3HT-<i>b</i>-sPP). Four
diblock copolymers with various sPP block lengths, P3HT<sub>16K</sub>-<i>b-</i>sPP<sub>3K</sub> (P1), P3HT<sub>16K</sub>-<i>b-</i>sPP<sub>6KÂ </sub>(P2), P3HT<sub>16K</sub>-<i>b-</i>sPP<sub>9KÂ </sub>(P3), and P3HT<sub>16K</sub>-<i>b-</i>sPP<sub>14K</sub> (P4), were prepared by the click coupling of N<sub>3</sub>-capped sPP and ethynyl-capped P3HT. The stereoregular crystalline
block sPP developed different types of molecular stacking structures
and led the P3HT domains to pack lamellar edge-on structure with improved
charge transporting characteristics, as evidenced by the grazing incidence
wide-angle X-ray scattering (GIWAXS), atomic force microscopy (AFM),
and transmission electron microscopy (TEM). The FET hole mobilities
of P1–P3 thin films were 4.15 × 10<sup>–3</sup>, 4.16 × 10<sup>–2</sup>, and 3.95 × 10<sup>–3</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>, respectively,
which were up to 1 order of magnitude higher than that of the parent
P3HT thin film (1.43 × 10<sup>–3</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>). The crystalline-stereoregular
crystalline diblock P3HT-<i>b</i>-sPP demonstrates that
using the lattice matching concept could well clarify the molecular
stacking structure of conjugated polymer segments in order to further
improve the performance of organic electron devices
Synthesis, Morphology, and Sensory Applications of Multifunctional Rod–Coil–Coil Triblock Copolymers and Their Electrospun Nanofibers
We report the synthesis, morphology, and applications
of conjugated
rod–coil–coil 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 rod–coil
block copolymers would have potential applications for multifunctional
sensory devices
Synthesis and Characterization of All-Conjugated Graft Copolymers Comprised of n‑Type or p‑Type Backbones and Poly(3-hexylthiophene) Side Chains
All-conjugated graft copolymers containing
polyÂ(3-hexylthiophene)
(P3HT) side chains and both of p-type and n-type backbones that are
connected with all π-conjugated linkages were synthesized via
a two-step method involving the Stille coupling reaction and Kumada
catalyst-transfer polycondensation (KCTP). A series of naphthalene
diimide copolymers with different compositions of 3-(4′-chloro-3′-tolyl)Âthiophene
(CTT) units (PNDICTT) were designed as n-type backbones, while the
polyÂ(3-(4′-chloro-3′-tolyl)Âthiophene-<i>alt</i>-thiophene) (PCTT) was designed as a p-type backbone which were converted
into n-type or p-type macroinitiators, and P3HT side chains were then <i>in situ</i> grafted from the macroinitiators via an externally
initiated KCTP at room temperature. By using this newly developed
two-step method for the synthesis of all-conjugated graft copolymers,
the number of P3HT side chains in the graft copolymers can be simply
controlled by varying the composition of the CTT units in PNDICTT.
Meanwhile, the chain length of P3HT was controllable by varying the
feed molar ratio of the thiophene monomer to CTT unit during the KCTP.
The optical and electrochemical properties of the all-conjugated graft
copolymers were investigated by UV–vis, cyclic voltammetry
(CV), and organic field-effect transistor (OFET) measurements. Moreover,
the differential scanning calorimetry (DSC) and grazing incident wide-angle
X-ray scattering (GIWAXS) results revealed that there were two distinguished
crystalline domains in the thin films of the graft copolymer. The
morphology of the graft copolymers was first observed by transmission
electron microscopy (TEM), in which there was a microphase separation
between the PNDICTT and P3HT domains, and the P3HT domains showed
partial nanofibril structures with a width of 10–20 nm
Interplay of Molecular Orientation, Film Formation, and Optoelectronic Properties on Isoindigo- and Thienoisoindigo-Based Copolymers for Organic Field Effect Transistor and Organic Photovoltaic Applications
A systematic study on the effects
of heteroarenes on the solid
state structure and optoelectronic properties of isoindigo analogues,
namely, PBDT-IIG and PBDT-TIIG, used in solution-processed organic
field effect transistors (OFETs) and organic photovoltaics (OPVs)
is reported. We discover that the optical absorption, frontier orbitals,
backbone coplanarity, molecular orientation, solubility, film morphology,
charge carrier mobility, and solar cell performance are critically
influenced by the heteroarenes in the acceptor subunits. PBDT-IIG
exhibits good p-type OFET performance with mobility up to 1.03 ×
10<sup>–1</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>, whereas PBDT-TIIG displays ambipolar mobilities
of μ<sub>h</sub> = 7.06 × 10<sup>–2</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> and μ<sub>e</sub> = 2.81 × 10<sup>–4</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>. PBDT-IIG and PBDT-TIIG blended
with [6,6]-phenyl-C<sub>71</sub>-butyric acid methyl ester (PC<sub>71</sub>BM) yield promising power conversion efficiencies (PCEs)
of 5.86% and 2.55%, respectively. The excellent mobility of PBDT-IIG
can be attributable to the growing fraction of edge-on packing by
the interfacial surface treatment. Although PBDT-TIIG could construct
a long-range face-on packing alignment to meliorate its photocurrent
in OPV applications, the low open-circuit voltage caused by its high-lying
HOMO energy level and greater recombination demonstrates the trade-off
between light absorption and solar cell performance. Nevertheless,
PBDT-TIIG with a PCE of 2.55% is the highest reported PCE to date
for the TIIG-based systems