Showing papers by "Wen-Chang Chen published in 2020"

High-Performance Nonvolatile Organic Photonic Transistor Memory Devices using Conjugated Rod-Coil Materials as a Floating Gate.

Abstract: A novel approach for using conjugated rod-coil materials as a floating gate in the fabrication of nonvolatile photonic transistor memory devices, consisting of n-type Sol-PDI and p-type C10-DNTT, is presented. Sol-PDI and C10-DNTT are used as dual functions of charge-trapping (conjugated rod) and tunneling (insulating coil), while n-type BPE-PDI and p-type DNTT are employed as the corresponding transporting layers. By using the same conjugated rod in the memory layer and transporting channel with a self-assembled structure, both n-type and p-type memory devices exhibit a fast response, a high current contrast between "Photo-On" and "Electrical-Off" bistable states over 105 , and an extremely low programing driving force of 0.1 V. The fabricated photon-driven memory devices exhibit a quick response to different wavelengths of light and a broadband light response that highlight their promising potential for light-recorder and synaptic device applications.

High Mobility Preservation of Near Amorphous Conjugated Polymers in the Stretched States Enabled by Biaxially-Extended Conjugated Side-Chain Design

Abstract: Polymers with abundant amorphous domain should facilitate energy dissipation upon stretching, making near amorphous π-conjugated polymers have immense potential in realizing intrinsically stretchab...

Backbone Engineering of Diketopyrrolopyrrole-Based Conjugated Polymers through Random Terpolymerization for Improved Mobility–Stretchability Property

Abstract: Conjugated polymers synthesized through random terpolymerization have recently attracted great research interest due to the synergetic effect on the polymer's crystallinity and semiconducting properties. Several studies have demonstrated the efficacy of random terpolymerization in fine-tuning the aggregation behavior and optoelectronic property of conjugated polymers to yield enhanced device performance. However, as an influential approach of backbone engineering, its efficacy in modulating the mobility-stretchability property of high-performance conjugated polymers has not been fuller explored to date. Herein, a series of random terpolymers based on the diketopyrrolopyrrole-bithiophene (DPP-2T) backbone incorporating different amounts of isoindigo (IID) unit are synthesized, and their structure-mobility-stretchability correlation is thoroughly investigated. Our results reveal that random terpolymers containing a low IID content (DPP95 and DPP90) show enhanced interchain packing and solid-state aggregation to result in improved charge-transporting performance (can reach 4 order higher) compared to the parent polymer DPP100. In addition, owing to the enriched amorphous feature, DPP95 and DPP90 deliver an improved orthogonal mobility (μh) of >0.01 cm2 V-1 s-1 under a 100% strain, higher than the value (∼0.002 cm2 V-1 s-1) of DPP100. Moreover, DPP95 even yields 20% enhanced orthogonal μh retention after 800 stretching-releasing cycles with 60% strain. As concluded from a series of analyses, the improved mobility-stretchability property exerted by random terpolymerization arises from the enriched amorphous feature and enhanced aggregation behavior imposed by the geometry mismatch between different acceptors (DPP and IID). This study demonstrates that backbone engineering through rational random terpolymerization not only enhances the mobility-stretchability of a conjugated polymer but also realizes a better mechanical endurance, providing a new perspective for the design of high-performance stretchable conjugated polymers.

Morphology and properties of PEDOT:PSS/soft polymer blends through hydrogen bonding interaction and their pressure sensor application

Abstract: We report the effects of the composition on the stretchability and conductivity of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) polymer blends with soft polymers including poly(vinyl alcohol) (PVA), poly(acrylic acid) (PAA), and poly(methacrylic acid) (PMAA) and their application in pressure sensors. The composition–stretchability relationship was investigated with the stress–strain curves of the bulk films. Among these polymer blends, PAA-based blends outperformed in stretchability, attributed to the low glass transition temperature and ductile nature of PAA. And the composition–conductivity relationship was studied with conductive atomic force microscopy, Gaussian simulation and infrared spectroscopy. The PAA-based blends presented well-dispersed morphology for PEDOT and the strongest hydrogen bonding network between PAA and PEDOT:PSS was created through the blending, which gave rise to stable and high conductivity. Furthermore, the conductivity of the PEDOT:PSS/PAA blend at 20/80 wt ratio was largely increased (13 to 125 S cm−1) and stretchability (elongation at break) increased from 20 to 40% through methanol treatment. Finally, PAA-based blends treated with methanol were applied to the pressure sensor device, achieving a very high sensitivity of 39.90 kPa−1 at 20% tensile strain, a quick response time of around 49 ms, and a low detection limit of about 27.4 Pa. This study suggested a novel and facile approach to manipulate the structure and stretchability of the PEDOT:PSS polymer blending system for stretchable electronics.

Study on Intrinsic Stretchability of Diketopyrrolopyrrole-Based π-Conjugated Copolymers with Poly(acryl amide) Side Chains for Organic Field-Effect Transistors.

Abstract: The development of a π-conjugated polymer with hydrogen-bonding moieties has aroused great attention because of the improved molecular stacking and the hydrogen-bonding network. In this study, PDPPTVT (diketopyrrolopyrrole-thiophenevinylenethiophene) and PDPPSe (diketopyrrolopyrrole-selenophene) alkylated with a carbosilane (SiC8) side chain and poly(acryl amide) (PAM)-incorporated alkyl side chain were prepared, and their structure-performance and structure-stretchability correlation were evaluated. By incorporating the DPPTVT backbone and 0, 5, 10, or 20% PAM-incorporated alkyl side chain, the μh value could reach 2.0, 0.97, 0.74, and 0.42 cm2 V-1 s-1, respectively (P1 to P4). The polymer with the PDPPSe backbone and 5% PAM-incorporated alkyl side-chain (P5) exhibited the maximum μh value of 0.96 cm2 V-1 s-1. By extending the PAM moiety from the backbone with alkyl spacers, the solid-state packing and edge-on orientation can be properly maintained. Surprisingly, the PAM-incorporated alkyl side-chain can provide a hydrogen-bonding network serving as sacrificial bonding to mechanical deformation. Therefore, the relevant changes in the crystallographic parameters including the crystalline size and the in-plane π-π stacking distance with a 100% external strain were less than 4 and 0.8%, respectively, from P1 to P3. Therefore, P3 achieved an excellent stretchability while maintaining its molecular orientation and charge-transporting performance. Even with 100% external strain, P3 still provided an orthogonal μh over 0.1 cm2 V-1 s-1. Moreover, by substituting the TVT moiety with the Se moiety, the ductility of the backbone can be further increased when the elastic modulus decreases from 0.80 to 0.36 GPa for P2 to P5. The achieved high μh retention is over 20% after 500 stretching-releasing cycles with a 60% external strain perpendicular to the channel direction for the polymer composed of PDPPSe and 5% PAM content. The results manifest that our newly designed DPP with the PAM-incorporated alkyl side chain provides a promising approach to promote the intrinsic stretchability of the π-conjugated polymers.

Inducing Molecular Aggregation of Polymer Semiconductors in a Secondary Insulating Polymer Matrix to Enhance Charge Transport

Abstract: Polymer semiconductors (PSCs) are a desirable class of materials for next-generation electronics. However, the conformational complexity associated with macromolecules, as well as the presence of u...

Two-Dimensional Cs2Pb(SCN)2Br2-Based Photomemory Devices Showing a Photoinduced Recovery Behavior and an Unusual Fully Optically Driven Memory Behavior.

Abstract: The rapid development of Internet of Things and big data has made the conventional storage devices face the need of reforming. Rather than using electrical pulses to store data in one of two states, photomemory exploiting optical stimulation to store light information emerges as a revolutionary candidate for the optoelectronic community. However, fully optically driven photomemory with fast data transmission speed and outstanding energy saving capability suffers from less exploration. Herein, a transistor-type photomemory using a 2D Cs2Pb(SCN)2Br2/polymer hybrid floating gate is explored and three host polymers, polystyrene, poly(4-vinylphenol), and poly(vinylpyrrolidone) (PVP), are investigated to understand the relationship between polymer matrix selection and memory performance. All devices show a photoinduced recovery memory behavior but with two distinctly different photomemory behaviors. In addition to the demonstration of a regular nonvolatile photomemory showing a high on/off ratio of >106 over 104 s, an unusual fully optically driven memory behavior is intriguingly accomplished in the Cs2Pb(SCN)2Br2/PVP photomemory. Using white light as the driver of programming and a blue laser as the main performer of erasing, this device can be switched between two distinguishable states and possesses acceptable data discriminability, as evidenced by its fully optically driven writing (programing)-reading-erasing-reading switching function that shows an on/off current ratio of 103. This study not only presents the first 2D perovskite-based photomemory but also shows a novel fully optically driven memory that has been rarely reported in the literature.

An Intrinsically Stretchable and Ultrasensitive Nanofiber-Based Resistive Pressure Sensor for Wearable Electronics

Abstract: To date, most skin-like pressure sensors largely depend on the conventional lithography technique for fabricating microstructures, limited by chemical-intensive and time-consuming manufacturing processes, which have limited the implementation scalability. Herein, we present the nano-resistor alongside fibrous interlocked microstructure (FIM) concept integrating a one-step electrospinning technique, which is a cost-effective, lithographic-free approach with large-scale expandability to fabricate skin-inspired resistive-type pressure sensors with ultrahigh performance and lightweight characteristics. The unique elastic sandwich-structured conducting nanofiber (ESSCN) configuration comprises poly(styrene-block-ethylene-ran-butylene-block-styrene) (SEBS) natural rubber and silver nanoparticles (AgNPs), while dielectric SEBS nanofibers are employed as the middle layer, sandwiched by two SEBS/AgNP electrodes at the top and bottom for packaging. The FIM endows the obtained pressure sensors with superior performance, including an ultrahigh sensitivity of 71.07 kPa−1 under a small applied pressure ( 5000 cycles) with excellent off/on switching behaviors, and mechanical stimuli sensing (pressure, strain, and bending). As a proof-of-concept demonstration, the sensors can be implemented through integration with an RGB-LED wristband and garments for monitoring human physiological signals, thereby endowing our ESSCN with broader potential applications in versatile electronic skin and human–machine interfaces.

Electrospinning-induced elastomeric properties of conjugated polymers for extremely stretchable nanofibers and rubbery optoelectronics

Abstract: The appealing advantage of using an electrospinning technique to improve the elastomeric properties of conjugated polymers is demonstrated in this study. It is revealed that the electrospinning process can strengthen the low-crystalline feature of the prepared nanofibers. By combining the use of a polymer with low glass transition temperature, extremely stretchable nanofibers can be successfully prepared. P-type poly(3-hexylthiophene-2,5-diyl) (P3HT) electrospun (ES) nanofibers show a low Young's modulus of 0.448 GPa and still exhibit a high hole mobility of >10−2 cm2 V−1 s−1 even under an external strain of 500%. Based on these prepared P3HT ES nanofibers, a fully stretchable field-effect transistor (FET) and photomemory are realized. Besides, stretchable n-type poly{[N,N′-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} (N2200) ES nanofibers are also successfully prepared with strain tolerance up to 400% strain, showing the general applicability of our proposed method.

Highly Stretchable Semiconducting Polymers for Field-Effect Transistors through Branched Soft–Hard–Soft Type Triblock Copolymers

Abstract: In this study, poly(3-hexylthiophene)-block-poly(δ-decanolactone)s (P3HT-b-PDLs) with the molecular architecture of AB, BAB, B2AB2, and B3AB3 (A: P3HT, B: PDL) were synthesized for stretchable orga...

Thermally and Mechanically Stable Polyimides as FlexibleSubstrates for Organic Field-Effect Transistors

Abstract: Highly thermal-mechanical stable polymers have attracted extensive research interest as substrates for flexible or wearable electronic devices, such as polyimides (PIs) Here, we report a class of

Environmentally Friendly Resistive Switching Memory Devices with DNA as the Active Layer and Bio-Based Polyethylene Furanoate as the Substrate

Abstract: The development of flexible electronics for wearable or implantable devices has become an exciting research area in recent years. With the transition from rigid to flexible devices, polymeric mater...

Carbohydrates as Hard Segments for Sustainable Elastomers: Carbohydrates Direct the Self-Assembly and Mechanical Properties of Fully Bio-Based Block Copolymers

Abstract: A series of fully bio-based block copolymers (BCPs) consisting of maltooligosaccharides (maltose, maltotriose, maltotetraose, and maltohexaose; A block) and poly(δ-decanolactone) (PDL; B block), wi...

Organic–Inorganic Nanocomposite Film for High‐Performance Stretchable Resistive Memory Device

Abstract: A compatible organic/inorganic nanocomposite film for a stretchable resistive memory device with high performance is demonstrated using poly(4-vinylpyridine)-block-poly(propyl methacrylate) (P4VP-b-PPMA) with zinc oxide (ZnO) nanoparticle. The PPMA soft segment is designed for reducing the rigidity of the active layer, while the P4VP block serves as a charge-trapping component to induce conductive filament and also a compatible moiety for inorganic nanoparticles through hydrogen bonding. The experimental results show that the P4VP-b-PPMA-based electrical memory device exhibits write-once-read-many-times memory behavior and an excellent ON/OFF current ratio of over 105 with a stable turn-on voltage (Vset ) around -2.0 V and stable memory behavior upon stretching up to 60% strain. On the other hand, P4VP-b-PPMA/ZnO nanocomposite film switches the memory characteristic to the dynamic random access memory behavior. The stretchable memory device prepared from the nanocomposite film can have a stretching durability over 40% strain and up to 1000 times cycling stretch-relaxation test. This work demonstrates a new strategy using nanocomposite films with tunable electrical characteristics and enhanced mechanical properties for stretchable electrical devices.

Development of Block Copolymers with Poly(3-hexylthiophene) Segments as Compatibilizers in Non-Fullerene Organic Solar Cells

Abstract: Poly(3-hexylthiophene) (P3HT)-segment-based block copolymers have been reported to deliver an effective compatibilizer function in the P3HT:PC61BM bulk-heterojunction (BHJ) system to simultaneously improve performance and stability. However, as limited by the deficient optophysic properties of the P3HT:PC61BM system, the resultant power conversion efficiency (PCE) of compatibilizer-mediated devices is low despite the optimized chemical structures of the P3HT-segment-based block copolymers. To better shed light on such a compatibilizer effect, the compatibilizer function of the P3HT-segment-based block copolymers is herein investigated in the emerging non-fullerene acceptor (NFA)-based BHJ systems. A P3HT analogue, poly[(4,4'-bis(2-butyloctoxycarbonyl-[2,2'-bithiophene]-5,5-diyl)-alt-(2,2'-bithiophene-5,5'-diyl))] (PDCBT), is used as the polymer donor since it shares the same backbone as P3HT to afford good compatibility with the P3HT-segment-based block copolymers and it has been proven to deliver a higher PCE than P3HT in the NFA BHJ systems. The P3HT-segment-based block copolymers (P1-P4) are manifested to offer similar compatibilizer functions for the PDCBT-based NFA BHJ systems, and the importance of their structural design is also revealed. As a result, addition of P4 delivers the largest enhancement in PCE: from 5.30 to 7.11% for the PDCBT:ITIC blend and from 6.21 to 8.04% for the PDCBT:IT-M blend. Moreover, it can also enhance the device's thermal stability, which can maintain 77% of the initial PCE after annealing at 85 °C for 120 h (for the PDCBT:ITIC blend), outperforming the pristine binary device (66% preservation). More importantly, the entire compatibilizer-mediated device exhibits an improved Voc. Such reduced potential loss can be attributed to the improved interfacial compatibility between the photoactive components, the most important function of a compatibilizer.

Improving the Performance and Stability of Perovskite Light-Emitting Diodes by a Polymeric Nanothick Interlayer-Assisted Grain Control Process.

Abstract: CsPbBr3 is a promising light-emitting material due to its wet solution processability, high photoluminescence quantum yield (PLQY), narrow color spectrum, and cost-effectiveness. Despite such advantages, the morphological defects, unsatisfactory carrier injection, and stability issues retard its widespread applications in light-emitting devices (LEDs). In this work, we demonstrated a facile and cost-effective method to improve the morphology, efficiency, and stability of the CsPbBr3 emissive layer using a dual polymeric encapsulation governed by an interface-assisted grain control process (IAGCP). An eco-friendly low-cost hydrophilic polymer poly(vinylpyrrolidone) (PVP) was blended into the CsPbBr3 precursor solution, which endows the prepared film with a better surface coverage with a smoothened surface. Furthermore, it is revealed that inserting a thin PVP nanothick interlayer at the poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS)/emissive layer interface further promotes the film quality and the performance of the derived LED. It is mainly attributed to three major consequences: (i) reduced grain size of the emissive layer, which facilitates charge recombination, (ii) reduced current leakage due to the enhanced electron-blocking effect, and (iii) improved color purity and air stability owing to better defect passivation. As a result, the optimized composite emissive film can retain the luminescence properties even on exposure to ambient conditions for 80 days and ∼62% of its initial PL intensity can be preserved after 30 days of storage without any encapsulation.

Investigation of the Mobility–Stretchability Relationship of Ester-Substituted Polythiophene Derivatives

Abstract: Poly(3-hexylthiophene) (P3HT) has been one of the most important organic semiconductors in the past few decades. To date, considerable effort has been dedicated toward improving its charge mobility...

Nanostructure- and Orientation-Controlled Resistive Memory Behaviors of Carbohydrate-block-Polystyrene with Different Molecular Weights via Solvent Annealing.

Abstract: We report the resistive electrical memory characteristics controlled by the self-assembled nanostructures of maltoheptaose-block-polystyrene (MH-b-PS) block copolymers, where the MH and PS blocks p...

Structure-Mobility Relationship of Benzodithiophene-Based Conjugated Polymers with Varied Biaxially-Extended Conjugated Side Chains

Abstract: Semi-two-dimensional (semi-2D) benzo[1,2-b:4,5-b′]dithiophene (BDT)-based donor–acceptor copolymers have been regarded as one of the most successful organic semiconductors for photovoltaic applicat...

Nano-Micro Dimensional Structures of Fiber-Shaped Luminous Halide Perovskite Composites for Photonic and Optoelectronic Applications.

Abstract: Perovskite nanomaterials have been revealed as highly luminescent structures regarding their dimensional confinement. In particular, their promising potential lies behind remarkable luminescent properties, including color tunability, high photoluminescence quantum yield, and the narrow emission band of halide perovskite (HP) nanostructures for optoelectronic and photonic applications such as lightning and displaying operations. However, HP nanomaterials possess such drawbacks, including oxygen, moisture, temperature, or UV lights, which limit their practical applications. Recently, HP-containing polymer composite fibers have gained much attention owing to the spatial distribution and alignment of HPs with high mechanical strength and ambient stability in addition to their remarkable optical properties comparable to that of nanocrystals. In this review, the fabrication methods for preparing nano-microdimensional HP composite fiber structures are described. Various advantages of the luminescent composite nanofibers are also described, followed by their applications for photonic and optoelectronic devices including sensors, polarizers, waveguides, lasers, light-down converters, light-emitting diode operations, etc. Finally, future directions and remaining challenges of HP-based nanofibers are presented.

Eco-Friendly Polyfluorene/Poly(butylene succinate) Blends and Their Electronic Device Application on Biodegradable Substrates

Abstract: We report an environmentally friendly resistive switching memory device on a biodegradable Ecoflex elastomeric substrate using nontoxic and disintegrable polyfluorene/poly(butylene succinate) (PFN/...

Competing Molecular Packing of Blocks in a Lamella-Forming Carbohydrate- block -poly(3-hexylthiophene) Copolymer

Abstract: A molecular packing model of poly(3-hexylthiophene)-block-peracetylated maltopheptaose (P3HT-b-AcMal7) was proposed based on the X-ray and electron diffraction measurements. The P3HT and AcMal7 seg...

An ultra heat-resistant polyimide formulated with photo-base generator for alkaline-developable, negative-type photoresist

Abstract: An alkaline-developable and negative-type photosensitive polyimide (PSPI) based on poly(amic acid) (PAA) and a photo-base generator (PBG) has been developed by using chemical amplification method. The PAA(PDA-BPDA) is composed of p-phenylenediamine (PDA) and 4,4′-biphtalic dianhydride (BPDA), and the derived PI possesses excellent thermal and thermo mechanical stability due to the highly rigid and linear backbone. The photolithographic parameters for the PSPI including the PBG content, post-exposure baking (PEB) temperature, PEB time and the molecular weight of the PAA was investigated with the adoption of (E)-3-(2-hydroxy-4-methoxyphenyl)-1-(piperidin-1-yl)prop-2-en-1-one (HMPP) as the PBG. The PSPI based on PAA(PDA-BPDA) with a molar ratio of 0.9/1.0 between PDA and BPDA, and HMPP (15 wt% to PAA) showed a sensitivity of 142 mJ/cm2 and contrast of 0.58 when exposed to 365-nm light (i-line), PEB at 170 °C for 5 min, and developed with an aqueous solution of 2.38 wt% tetramethylammonium hydroxide and isopropanol. A clear negative 4-μm feature pattern was obtained and imidized into the PI pattern upon heating at 250 °C, confirming by scanning electron microscopy. This is the first work to utilize a highly rigid backbone with high thermal stability for PSPIs. The outstanding thermal and thermo mechanical stability manifests that developed PSPIs is highly potential in the microelectronics.

Nuclear dependence of light neutral meson production in p-A collisions at 400 GeV with NA60

Abstract: The NA60 experiment has studied low-mass muon pair production in proton-nucleus collisions with a system of Be, Cu, In, W, Pb and U targets, using a 400 GeV proton beam at the CERN SPS. The transverse momentum spectra of the $\rho/\omega$ and $\phi$ mesons are measured in the full $p_\mathrm{T}$ range accessible, from $p_\mathrm{T} = 0$ up to 2 GeV/$c$. The nuclear dependence of the production cross sections of the $\eta$, $\omega$ and $\phi$ mesons has been found to be consistent with the power law $\sigma_\mathrm{pA} \propto \mathrm{A}^\alpha$, with the $\alpha$ parameter increasing as a function of $p_\mathrm{T}$ for all the particles, and an approximate hierarchy $\alpha_\eta \approx \alpha_\phi > \alpha_\omega$. The cross section ratios $\sigma_\eta/\sigma_\omega$, $\sigma_\rho/\sigma_\omega$ and $\sigma_\phi/\sigma_\omega$ have been studied as a function of the size A of the production target, and an increase of the $\eta$ and $\phi$ yields relative to the $\omega$ is observed from p-Be to p-U collisions.