Showing papers by "Wen-Chang Chen published in 2019"

Stretchable and Ambient Stable Perovskite/Polymer Luminous Hybrid Nanofibers of Multicolor Fiber Mats and Their White LED Applications.

Abstract: We report the fabrication and optical/mechanical properties of perovskite/thermoplastic polyurethane (TPU)-based multicolor luminescent core-shell nanofibers and their large-scale fiber mats. One-step coaxial perovskite/TPU nanofibers had a high photoluminescence quantum yield value exceeding 23.3%, surpassing that of its uniaxial counterpart, due to the homogeneous distribution of perovskite nanoparticles (NPs) by the confinement of the TPU shell. The fabricated core-shell nanofibers exhibited a high mechanical endurance owing to the well elastic properties of TPU and maintained the luminescence intensity even under a 100% stretched state after 1000 stretching-relaxing cycles. By taking advantage of the hydrophobic nature of TPU, the ambient and moisture stability of the fabricated fibers were enhanced up to 1 month. Besides, large-area stretchable nanofibers with a dimension of 15 cm × 30 cm exhibiting various visible-light emission peaks were fabricated by changing the composition of perovskite NPs. Moreover, a large-scale luminescent and stretchable fiber mat was successfully fabricated by electrospinning. Furthermore, the white-light emission from the fabricated fibers and mats was achieved by incorporating orange-light-emitting poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] into the TPU shell and coupling the turquoise blue-light-emitting perovskite NPs in the core site. Finally, the integrity of the perovskite-based TPU fibers was realized by fabricating a light-emitting diode (LED) device containing the orange-light-emitting fibers embedded in the polyfluorene emissive layer. This work demonstrated an effective way to prepare stable and stretchable luminous nanofibers and the integration of such nanofibers into LED devices, which could facilitate the future development of wearable electronic devices.

Tailoring Carbosilane Side Chains toward Intrinsically Stretchable Semiconducting Polymers

Abstract: Carbosilane side chain-equipped isoindigo–bithiophene semiconducting polymers (PII2T) have been designed and synthesized for stretchable electronics applications. Systematically tailoring the lengt...

Multilevel Photonic Transistor Memory Devices Using Conjugated/Insulated Polymer Blend Electrets

Abstract: Photonic data storage has diverse optoelectronic applications such as optical sensing and recording, integrated image circuits, and multibit-storage flash memory. In this study, we employ conjugated/insulated polymer blends as the charge storage electret for photonic field-effect transistor memory devices by exploring the blend composition, energy level alignment, and morphology on the memory characteristics. The studied conjugated polymers included poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PF), poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), poly[{2,5-di(3',7'-dimethyloctyloxy)-1,4-phenylene-vinylene}-co-{3-(4'-(3″,7″-dimethyloctyloxy)phenyl)-1,4-phenylenevinylene}-co-{3-(3'-(3',7'-dimethyloctyloxy)phenyl)-1,4-phenylenevinylene}] (SY-PPV), and poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)] (F8BT), and the insulated polymers were polystyrene (PS) and poly(methyl methacrylate) (PMMA). The photonic memory device using the PF/PS blend electret exhibited a dynamic switching behavior with light-writing and voltage-erasing processes both within only 1 s, along with a high contrast on the current on/off ratio between "Photo-On" and "Electrical-OFF" over 106 and the decent retention time for more than 3 months. In addition, the multilevel memory behavior could be observed using different light sources of 405, 450, and 520 nm or energy intensity, which was supported by surface potential analysis. The characteristics were superior to those of the devices using PF/PMMA blend due to the higher charge storage behavior of PS supported by fluorescence analysis. The PF/PS blend film prepared from the chlorobenzene solvent exhibited mesh-like and aggregated PF domains in the PS matrix and enhanced the contact surface area between the semiconductor and blend electret, leading to a higher memory window. The photonic memory behavior was also observed in the blend electrets of PS with the low band gap polymer, MEH-PPV, SY-PPV, or F8BT, by changing the photoresponsive light sources. Our study demonstrated a new electret system to apply on the multilevel photonic memory devices.

Asymmetric Side-Chain Engineering of Isoindigo-Based Polymers for Improved Stretchability and Applications in Field-Effect Transistors

Abstract: Thus far, there is still no study systematically investigating the influence of asymmetric side-chain design on a polymer's stretchability and its associated stretchable device applications. Herein, three kinds of asymmetric side chains consisting of carbosilane side chain (Si-C8), siloxane-terminated side chain (SiO-C8), and decyltetradecane side chain (DT) are engineered in isoindigo-bithiophene (PII2T, P1-P3) and isoindigo-difluorobithiophene (PII2TF, P4-P6) conjugated polymers, and their structure-stretchability correlation is explored in field-effect transistor characterization. It is revealed that owing to the geometric difference between the side chains, different asymmetric side-chain combinations impose distinct influences on the molecular stacking and orientation of the derived polymers. Surprisingly, the combination of asymmetric side chains and backbone fluorination is shown to deliver the best stretchability and mechanical durability of the derived polymer. Consequently, P6 consisting of asymmetric Si-C8/DT side chains and fluorinated backbone possesses the best mobility preservation of 81% at 100% strain with the stretching force perpendicular to the charge-transporting direction. Moreover, it presents 90% mobility retention after 400 stretching-releasing cycles with 60% strain, greatly exceeding the value (36%) of the non-fluorinated counterpart (P3). Our results suggest that the rational design of asymmetric side chains and backbone fluorination provides an efficient way to enhance the intrinsic stretchability of conjugated polymers.

Enhanced Near-Infrared Photoresponse of Inverted Perovskite Solar Cells Through Rational Design of Bulk-Heterojunction Electron-Transporting Layers.

Abstract: How to extend the photoresponse of perovskite solar cells (PVSCs) to the region of near-infrared (NIR)/infrared light has become an appealing research subject in this field since it can better harness the solar irradiation. Herein, the typical fullerene electron-transporting layer (ETL) of an inverted PVSC is systematically engineered to enhance device's NIR photoresponse. A low bandgap nonfullerene acceptor (NFA) is incorporated into the fullerene ETL aiming to intercept the NIR light passing through the device. However, despite forming type II charge transfer with fullerene, the blended NFA cannot enhance the device's NIR photoresponse, as limited by the poor dissociation of photoexciton induced by NIR light. Fortunately, it can be addressed by adding a p-type polymer. The ternary bulk-heterojunction (BHJ) ETL is demonstrated to effectively enhance the device's NIR photoresponse due to the better cascade-energy-level alignment and increased hole mobility. By further optimizing the morphology of such a BHJ ETL, the derived PVSC is finally demonstrated to possess a 40% external quantum efficiency at 800 nm with photoresponse extended to the NIR region (to 950 nm), contributing ≈9% of the overall photocurrent. This study unveils an effective and simple approach for enhancing the NIR photoresponse of inverted PVSCs.

Solvent Effects on Morphology and Electrical Properties of Poly(3-hexylthiophene) Electrospun Nanofibers.

Abstract: Herein, poly(3-hexylthiophene-2,5-diyl) (P3HT) nanofiber-based organic field-effect transistors were successfully prepared by coaxial electrospinning technique with P3HT as the core polymer and poly(methyl methacrylate) (PMMA) as the shell polymer, followed by extraction of PMMA. Three different solvents for the core polymer, including chloroform, chlorobenzene and 1,2,4-trichlorobenzene, were employed to manipulate the morphologies and electrical properties of P3HT electrospun nanofibers. Through the analyses from dynamic light scattering of P3HT solutions, polarized photoluminescence and X-ray diffraction pattern of P3HT electrospun nanofibers, it is revealed that the P3HT electrospun nanofiber prepared from the chloroform system displays a low crystallinity but highly oriented crystalline grains due to the dominant population of isolated-chain species in solution that greatly facilitates P3HT chain stretching during electrospinning. The resulting high charge-carrier mobility of 3.57 × 10−1 cm2·V−1·s−1 and decent mechanical deformation up to a strain of 80% make the P3HT electrospun nanofiber a promising means for fabricating stretchable optoelectronic devices.

The green poly-lysine enantiomers as electron-extraction layers for high performance organic photovoltaics

Abstract: In this study, we first revealed green materials – poly-lysines (poly-L-lysine and poly-L-lysine blend poly-D-lysine) – as electron-extraction layers (EELs) in organic photovoltaics (OPVs). The distinct configurations of poly-lysine enantiomers were verified by conducting zeta potential analysis, and their work function (WF)-tuning capabilities for indium tin oxide (ITO) were affirmed by ultraviolet photoelectron spectroscopy (UPS). These two poly-lysine groups, with different arrangements of the amino groups that built up different surface dipoles on the ITO substrate, altered the surface energy and WF of ITO. Poly-L-lysine optimized the WF of ITO for efficient carrier transport in the OPV device, in the electron transporting layer-free OPV devices, and we observed a high power conversion efficiency (PCE) of 10.01% in the device configuration of ITO/interlayer/BHJ/MoO3/Ag. As the first examination of poly-lysine enantiomers for OPVs, we provided the WF-tuning functions – increasing polarity as an interfacial dipole is formed at the corresponding interface, and discovered a promising interfacial material possessing high efficiency and benefitting from a long-term stability to perform in a stable PCE with about 80% of its original PCE remaining after continuous heat and light treatment for 400 hours.

Donor–Acceptor Core–Shell Nanoparticles and Their Application in Non‐Volatile Transistor Memory Devices

Abstract: Donor-acceptor crosslinked poly[poly(ethylene glycol) methyl ether-methacrylate]-block-poly[1,1'-bis(2-ethylpentyl)-6-methyl-6'-(5-methyl-3-vinylthiophen-2-yl)-[3,3'-biindoline]-2,2'-dione] (poly(PEGMA)m -b-poly(VTIID)n ) nanoparticles with various vinylthiophene donor/isoindigo acceptor ratios are synthesized successfully. The prepared nanoparticles have uniform sizes and well-defined core-shell nanostructures. The intramolecular charge transfer is effectively enhanced due to the incorporation of acceptor groups after the crosslinking reaction. A transistor memory device is assembled using the synthesized polymer and has nonvolatile flash-type memory and amphiphilic trapping behavior. The optimized devices exhibit a significant memory window of approximately 38 V, a retention ability of over 104 s, and an endurance of at least 100 cycles. This study examines multiple applications of crosslinked core-shell nanoparticles, which demonstrates their promise as charge-storage dielectric materials for use in organic memory devices.

Robust Sub-10 nm Pattern of Standing Sugar Cylinders via Rapid “Microwave Cooking”

Abstract: Block copolymer self-assembly is a widely used technique for obtaining many interesting nanostructures. Development of efficient and rapid processes for driving block copolymer selfassembly has remained a challenge. Microwave heating has attracted much attention in bioenergy production and food industry due to the advantages associated with dielectric heating effects. We report here a simple method (like microwave cooking) of microwave-heatinginduced microphase separation of a carbohydrate-based block copolymer, maltoheptaose-block

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 $$2 \, {\hbox {GeV/c}}$$ . 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.

Fabrication and electrical characterization of High-Voltage silicon JFETs

Abstract: Motivated by the need of a rad-hard switch to be used in the future ATLAS Inner Tracker detector (ITk), at Brookhaven National Laboratory we conceived a High-Voltage silicon vertical JFET capable of satisfying most of the strict specifications required for such a switch. By using the available planar technology for the silicon processing, we fabricated in our Clean Room dedicated batches of HV JFETs, first n-type and then p-type channel JFETs. The electrical characterization showed in particular high voltage handling capabilities in the OFF state, for both types of JFETs. In this paper, we describe the design, the fabrication steps and we report the electrical characterization.

Investigation of Trench Technology on Silicon Device Fabrication

Abstract: This work was motivated by the possibility of simplifying the process steps on silicon device fabrication. This simplification could benefit other silicon detector fabrications and have the possibility of terminating the junction edges in other detector designs. This is our attempt of exploring the RIE trench technique onto silicon device process. This technique originated from the high-purified germanium (HPGe) detector fabrication. The results have shown good pixel isolations. It has also shown that the multiple guards to lower the potential from the active area are more effective for trenched guard rings than the planar-processed guard rings. Furthermore, it has shown that the inter-pixel capacitance decreases as the trench depth increases.

Proton Irradiation-Induced Random Telegraph Signal Noise in a $2\text{k}\times2\text{k}$ 4T CMOS Active Pixel Sensor: Testing, Detection, and Modeling

Abstract: This paper presents our recent study progress on proton-irradiated-induced random telegraph signal (RTS) in a high-resolution CMOS active pixel sensor (APS). First, RTS waveforms of a commercial $2\text{k} \times2\text{k}$ 4T CMOS APS chip in 180-nm CMOS technology are tested under the 10-MeV proton irradiation. Second, a novel adaptive automatic detection method (AADM) based on real-time thresholds is proposed for the sequential processing of a large batch of RTS pixels. Real-time thresholds and two-stage reconstruction algorithms are employed to improve the validity and correctness of RTS reconstruction. The proposed detection method which can realize the batch autoprocessing by using an adaptive filter will improve the detection efficiency. Third, a new approach to model the RTS maximum transition amplitude distribution is presented. It has been proven that the double exponential distribution can fit the RTS maximum transition amplitude distribution better. Two models are proposed to predict the contributions due to the ionizing effects and displacement damage effects. Finally, the error analysis is given. The errors between the simulated data of the proposed models and experimental results are all less than 5.5 %.