Synthesis and Characterization of Rod−Coil Polymers Based on Poly(ethylene oxide)s and Novel Luminescent Aromatic Cores

A novel conjugated aromatic core containing direct-coupled fluorene, thiophene, and biphenyl groups via Suzuki coupling reaction was synthesized. The asymmetrical molecules contain two kinds of poly(ethylene oxide)s (PEO, Mn = 750 and 2000, n = 17 and 44) on one side of the rigid cores. Asymmetrical FOC8PEO17 and FOC16PEO17 contain flexible PEO chains (n = 17) displaying the smectic phases. However, FOC8PEO44 and FOC16PEO44 consisting of flexible PEO chains (n = 44) exhibit two kinds of columnar phases, Colh and Colr. Besides, alkoxy groups with different lengths (−OC8H17and −OC16H33) on both sides of the rigid cores were used as another flexible chain to form symmetrical molecules. Symmetrical FOC8 and FOC16 exhibit the nematic and smectic mesophases, respectively. Optical textures (POM) and XRD patterns have confirmed the structure of the mesophases and the molecular arrangements. The photophysical characteristics of all luminescent compounds were studied by photoluminescence and UV−vis absorption. In addition, a series of double-layered PLED devices with the configuration of PVK:emitters(100:8 by weight)/TPBI/MgAg/Ag were fabricated and investigated

Structural Evolution of Poly(styrene-<i>b</i>-4-vinylpyridine) Diblock Copolymer/Gold Nanoparticle Mixtures from Solution to Solid State

We used in situ annealing small-angle X-ray scattering to monitor the structural evolution of a spherical poly(styrene-b-4-vinylpyridine) diblock copolymer (PS-b-P4VP)/2-phenylethanethiol-coated Au nanoparticle (AuSC2Ph) mixture in the solid state during its thermal annealing. We found that the Au nanoparticles (NPs) that existed initially in a random state with some cluster packing in the PS domain diffused to the interface of the amphiphilic PS-b-P4VP diblock copolymer within 4 h at 170 °C under vacuum to form NP-filled shell-like assemblies, as further evidenced from transmission electron microscopy imaging. From the X-ray photoelectron spectroscopy data, we speculate that this interfacial activity of AuSC2Ph results from the fact that the initially hydrophobic Au NP surfaces became increasingly hydrophilic as most of the 2-phenylethanethiol ligands had evaporated off. The Au NP nanoshell assemblies located at the interface between PS and P4VP were quite stable even after redissolving in toluene; they remained in the form of PS−Au−P4VP core/shell/corona onion micelles, as evidenced from solution state small-angle X-ray scattering data

Using a Solution Crystal Growth Method To Grow Arrays of Aligned, Individually Distinct, Single-Crystalline TiO₂ Nanoneedles within Nanocavities

Using a Solution Crystal Growth Method To Grow Arrays of Aligned, Individually Distinct, Single-Crystalline TiO2 Nanoneedles within Nanocavitie

Morphologies of Self-Organizing Regioregular Conjugated Polymer/Fullerene Aggregates in Thin Film Solar Cells

In this study, we used simultaneous synchrotron grazing incidence X-ray scattering and diffraction to elucidate the overall morphologies of bulk heterojunction (BHJ) thin film (ca. 100 nm) solar cells containing phase-separated poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) domains. Specifically, the dimensions and orientation of the P3HT crystallites and the sizes of the PCBM aggregates in BHJ thin films were determined. The appropriate PCBM aggregate size and density required for an optimum performance of the film in the photovoltaics device resulted in deteriorated ordering in the out-of-plane direction, but improved the in-plane packing of the P3HT lamellae. When the P3HT crystallites and PCBM aggregates had comparable domain sizes and number densities, the interpercolated networks for electron- and hole-transport were optimized in the film. This new understanding of the underlying mechanism of carrier mobility in BHJ thin films might be crucial in improving the efficiency of future solar cells

Plasma-Induced Exfoliation Provides Onion-Like Graphene-Surrounded MoS₂ Nanosheets for a Highly Efficient Hydrogen Evolution Reaction

With the goal of obtaining sustainable earth-abundant electrocatalyst materials displaying high performance in the hydrogen evolution reaction (HER), here we propose a facile one-pot plasma-induced electrochemical process for the fabrication of new core–shell structures of ultrathin MoS2 nanosheets engulfed within onion-like graphene nanosheets (OGNs@MoS2). The resultant OGNs@MoS2 structures not only increased the number of active sites of the semiconducting MoS2 nanosheets but also enhanced their conductivity. Our OGNs@MoS2 composites exhibited high HER performance, characterized by a low overpotential of 118 mV at a current density of 10 mA cm–2, a Tafel slope of 73 mV dec–1, and long-time stability of 105 s without degradation; this performance is much better than that of the sheet-like graphene-wrapped MoS2 composite GNs@MoS2 (182 mV, 82 mV dec–1) and is among the best ever reported for composites involving MoS2 and graphene nanosheets prepared through a simple one-batch process and using a low temperature and a short time for the HER. This approach appears to be an effective and simple strategy for tuning the morphologies of composites of graphene and transition metal dichalcogenide materials for a broad range of energy applications

Plasma-Induced Exfoliation Provides Onion-Like Graphene-Surrounded MoS₂ Nanosheets for a Highly Efficient Hydrogen Evolution Reaction

With the goal of obtaining sustainable earth-abundant electrocatalyst materials displaying high performance in the hydrogen evolution reaction (HER), here we propose a facile one-pot plasma-induced electrochemical process for the fabrication of new core–shell structures of ultrathin MoS2 nanosheets engulfed within onion-like graphene nanosheets (OGNs@MoS2). The resultant OGNs@MoS2 structures not only increased the number of active sites of the semiconducting MoS2 nanosheets but also enhanced their conductivity. Our OGNs@MoS2 composites exhibited high HER performance, characterized by a low overpotential of 118 mV at a current density of 10 mA cm–2, a Tafel slope of 73 mV dec–1, and long-time stability of 105 s without degradation; this performance is much better than that of the sheet-like graphene-wrapped MoS2 composite GNs@MoS2 (182 mV, 82 mV dec–1) and is among the best ever reported for composites involving MoS2 and graphene nanosheets prepared through a simple one-batch process and using a low temperature and a short time for the HER. This approach appears to be an effective and simple strategy for tuning the morphologies of composites of graphene and transition metal dichalcogenide materials for a broad range of energy applications

Synthesis and Characterization of Pyrido[3,4-<i>b</i>]pyrazine-Based Low-Bandgap Copolymers for Bulk Heterojunction Solar Cells

We have used Stille polycondensation to prepare a series of low-bandgap copolymers, P1−P4, by conjugating the electron-accepting pyrido[3,4-b]pyrazine (PP) moieties with the electron-rich benzo[1,2-b:3,4-b′]dithiophene (BDT) or cyclopentadithiophene (CPDT) units. P1 and P3 are based on PP and BDT units while P2 and P4 are based on PP and CPDT units. All of these polymers exhibited excellent thermal stability and sufficient energy offsets for efficient charge transfer and dissociation, as determined through thermogravimetric analyses and cyclic voltammetry, respectively. The bandgaps of the polymers could be tuned in the range 1.46−1.60 eV by using the two different donors, which have different electron-donating abilities. The three-component copolymers, P3 and P4, incorporating the thiophene and bithiophene segments, respectively, absorbed broadly, covering the solar spectrum from 350 to 800 nm. The morphologies of the blends of P3 and P4 with [6,6]-phenyl-C70-butyric acid methyl ester (PC70BM) were more homogeneous than those of P1 and P2; in addition, devices incorporating the P3 and P4 blends exhibited superior performance. The best device performance resulted from an active layer containing the P4:PC70BM blend; the short-circuit current was 10.85 mA cm−2 and the power conversion efficiency was 3.15%

Pseudo-Single-Crystalline Self-Assembled Structure Formed from Hydrophilic CdSe and Hydrophobic Au Nanoparticles in the Polystyrene and Poly(4-vinylpyridine) Blocks, Respectively, of a Polystyrene-<i>b</i>-poly(4-vinylpyridine) Diblock Copolymer

Pseudo-Single-Crystalline Self-Assembled Structure Formed from Hydrophilic CdSe and Hydrophobic Au Nanoparticles in the Polystyrene and Poly(4-vinylpyridine) Blocks, Respectively, of a Polystyrene-b-poly(4-vinylpyridine) Diblock Copolyme

Enhanced Luminance and Thermal Properties of Poly(phenylenevinylene) Copolymer Presenting Side-Chain-Tethered Silsesquioxane Units

We have synthesized, using the Gilch polymerization method, a new series of high-brightness, soluble copolymers (POSS-PPV-co-MEHPPV) of poly(p-phenylenevinylene) (PPV) containing side-chain-tethered polyhedral oligomeric silsesquioxane (POSS) pendent units and poly(2-methoxy-5-[2-ethylhexyloxy]-1,4-phenylenevinylene) (MEHPPV). This particular molecular architecture of POSS-PPV-co-MEHPPV copolymers possesses not only a larger quantum yield (0.85 vs 0.19) but also higher degradation and glass transition temperatures relative to those of pure MEHPPV. The maximum brightness of a double-layered-configured light-emitting diode (ITO/PEDOT/emissive polymer/Ca/Al) incorporating a copolymer of MEHPPV and 10 mol % PPV-POSS was 5 times as large as that of a similar light-emitting diode incorporating pure MEHPPV (2196 vs 473 cd/m2)

Doping ZnO Electron Transport Layers with MoS₂ Nanosheets Enhances the Efficiency of Polymer Solar Cells

In this study, we incorporated molybdenum disulfide (MoS₂) nanosheets into sol–gel processing of zinc oxide (ZnO) to form ZnO:MoS₂ composites for use as electron transport layers (ETLs) in inverted polymer solar cells featuring a binary bulk heterojunction active layer. We could effectively tune the energy band of the ZnO:MoS₂ composite film from 4.45 to 4.22 eV by varying the content of MoS₂ up to 0.5 wt %, such that the composite was suitable for use in bulk heterojunction photovoltaic devices based on poly­[bis­(5-(2-ethylhexyl)­thien-2-yl)­benzodithiophene-<i>alt</i>-(4-(2-ethylhexyl)-3-fluorothienothiophene)-2-carboxylate-2,6-diyl] (PTB7-TH)/phenyl-C₇₁-butryric acid methyl ester (PC₇₁BM). In particular, the power conversion efficiency (PCE) of the PTB7-TH/PC₇₁BM (1:1.5, w/w) device incorporating the ZnO:MoS₂ (0.5 wt %) composite layer as the ETL was 10.1%, up from 8.8% for the corresponding device featuring ZnO alone as the ETL, a relative increase of 15%. Incorporating a small amount of MoS₂ nanosheets into the ETL altered the morphology of the ETL and resulted in enhanced current densities, fill factors, and PCEs for the devices. We used ultraviolet photoelectron spectroscopy, synchrotron grazing incidence wide-/small-angle X-ray scattering, atomic force microscopy, and transmission electron microscopy to characterize the energy band structures, internal structures, surface roughness, and morphologies, respectively, of the ZnO:MoS₂ composite films