Organic light-emitting diodes fabricated on recessed anodes for light extraction enhancement

Circular recesses have been fabricated on indium tin oxide (ITO) anodes to enhance light extraction of organic light-emitting diodes (OLEDs). The effects of recess depth and recess coverage ratio on the performance of a green OLED were systematically investigated. Results showed that the current efficiency could be enhanced from 40.7 cd/A of a planar device to 47.2 cd/A of the device with a recess depth of 100 nm and a recess coverage ratio of 14.1%. The enhanced light extraction by the recess wall effect was realized to be the major factor leading to the improved efficiency. The efficiency is however limited by the accompanying increase in electrical resistivity of the ITO films at deep recesses and high recess coverage ratios. Despite of the insignificant efficiency enhancement (up to 16%) in this study, this recessed ITO approach provides a simple architecture to enhance waveguide mode light extraction without adding an internal medium.     

Thermal,mechanical and structural investigation of copolyimide–silica hybrids containing phosphine oxide

In this study, a novel hybrid copolyimide was synthesized from copolyamic acid solutions (PAAs) obtained by the reaction between bis(3-aminophenoxy-4-phenyl)phenylphosphine oxide (m-BAPPO), 3,3′-diaminodiphenyl sulfone (DDS) and 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA), followed by thermal imidization. Hybrid materials containing 5% SiO₂ were synthesized by sol–gel technique. The polyimide–silica hybrids were characterized by Fourier Transform Infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Thermogravimetric analysis showed that the weight loss of hybrids is shifted to the higher temperature compared to the neat copolyimide. The contact angle measurements confirmed the hydrophobic surface of hybrids. Moreover, the gas permeability measurements were also done to take a step for forthcoming gas separation studies. The tensile modulus and strength of the copolyimides are good.     

Solid acid-catalyzed conversion of furfuryl alcohol to alkyl tetrahydrofurfuryl ether

The acidic zeolite HZSM-5 (Si/Al = 25) achieved 58.9% selectivity of methyl furfuryl ether (MFE) and 44.8% selectivity of ethyl furfuryl ether (EFE) from etherification of furfuryl alcohol with methanol and ethanol. MFE and EFE were quantitatively hydrogenated into methyl tetrahydrofurfuryl ether (MTE) and ethyl tetrahydrofurfuryl ether (ETE) using a Raney Ni catalyst.     

Acceptor-rich bulk heterojunction polymer solar cells with balanced charge mobilities

In this work, we reported efficient polymer solar cells with balanced hole/electron mobilities tuned by the acceptor content in bulk heterojunction blend films. The photovoltaic cells were fabricated with two new wide band-gap D-A polymers PBDDIDT and PBDDIDTT as the donor material. The molecular conformations of new polymers are carefully evaluated by theoretical calculations. The results of photovoltaic studies show that two devices reach their optimal conditions with rich PC₇₁BM content up to 80% in blend films, which is uncommon with most of reported PSCs. The as-cast devices based on PBDDIDT and PBDDIDTT reveal good photovoltaic performance with PCE of 7.04% and 6.40%, respectively. The influence of PC₇₁BM content on photovoltaic properties is further detailed studied by photoluminescence emission spectra, charge mobilities and heterojunction morphology. The results exhibit that more efficient charge transport between donor and acceptor occurs in rich PC₇₁BM blend films. Meanwhile, the hole and electron mobilities are simultaneously enhanced and afford a good balance in rich PC₇₁BM blend films (D/A, 1:4) which is critical for the improvement of current density and fill factors.     

Comparable Characterization of Nanocellulose Extracted from Bleached Softwood and Hardwood Pulps

In this study, the characteristics of nanocellulose extracted from bleached softwood and hardwood pulps by formic acid hydrolysis followed by TEMPO-mediated oxidation were compared using transmission electron microscopy (TEM), atomic force microscopy (AFM), Fourier transform infrared analysis (FT-IR), X-ray diffraction (XRD), and thermal gravimetric analysis (TGA). The experimental results showed that the nanocellulose products derived from spruce pulp exhibited a relatively larger particle size, higher crystallinity, and higher thermal stability, compared with the corresponding products obtained from aspen pulp under the same conditions. Furthermore, the study helped establish that the properties of the nanocellulose products were highly dependent on the nature of the starting materials under identical processing conditions.     

A new soluble poly(bithiophene)-co-3,4-di(methoxycarbonyl)methyl thiophene for LED

The regioregular polyalkylthiophene reported in this contribution has been electrochemically synthesised starting from a 3,4-bis-methoxyacetyl-terthiophene and carefully characterised. Photoluminescence analysis gave, both in solution and in films, very appreciable quantum yield values and LED devices realised with Ca cathode provided a value of red electroluminescence comparable with those of regioregular poly(3-alkylthiophene)s in the monolayer active material architecture, while if a blend with poly-N-vinylcarbazole and 2-(4-t-butyl-phenyl)-5-(4-biphenyl)-1,3,4-oxadiazole constitutes the active layer a white emission is observed.     

Boosting the Microbial Electrosynthesis of Acetate from CO2 by Hydrogen Evolution Catalysts of Pt Nanoparticles/rGO

Catalysis Letters - Microbial electrosynthesis (MES) is an effective approach to driving the CO2 reduction to multi-carbon organic products using renewable energy. In this work, the MES of acetate...     

Bifunctional doped transition metal CoSSeNi–Pt/C for efficient electrochemical water splitting

Reasonable design and synthesis of hetero atom metal coordination compounds on the atomic scale can significantly improve the performance of the catalysts. Herein, Pt/C (20%) is doped and inserted into the CoSSeNi catalyst through two steps of hydrothermal reaction and high temperature calcination process. Compared with the single metal Pt/C doped CoSSe–Pt/C, the bimetal doped CoSSeNi–Pt/C can greatly enhance the hydrogen evolution reaction (HER) activity. The optimized Pt content in CoSSeNi–Pt/C is 2.25 wt%, which achieves the optimal HER and OER activity. The OER and HER overpotentials of CoSSeNi–Pt/C-0.3 nanosheets at 10 mA cm^?2 only required 295 mV and 180 mV, respectively. During the accelerated durability test, in the presence of Pt/C dopants, CoSSeNi–Pt/C catalyst exhibited excellent long-time durability in alkaline media. Meanwhile, CoSSeNi–Pt/C showed much higher DOS near the Fermi level and the higher electron density near the Fermi level would facilitate the adsorption of adsorbates.     

Controlling singlet–triplet splitting in carbazole–oxadiazole based bipolar phosphorescent host materials

A rational molecular design strategy for carbazole–oxadiazole based bipolar host materials was developed to improve the device efficiency of blue phosphorescent organic light-emitting diodes (PHOLED). Steric effects of strategically placed methyl groups led to an increase of triplet energies (o-2MPCzPOXD: 2.66 eV and o-3MPCzPOXD: 2.73 eV versus the initial host material o-PczPOXD: 2.62 eV) while less pronouncedly affecting singlet energies and, therefore, retaining low driving voltages, high power efficiencies and remarkably low efficiency roll-offs in PHOLEDs. The maximum quantum efficiencies (EQE) for blue devices (FIrpic) were significantly raised for o-2MPCzPOXD (13.6%) and o-3MPCzPOXD (11.5%) versus o-PCzPOXD (9.0%) although yielding comparable values for green devices (Ir(ppy)₃; 12.9% and 15.4% versus 13.2%). Supported by theoretical calculations a structure–property relationship was established from photo-physical properties, PHOLED performance measurements and structural characterization from single crystal data.     

Green synthesis of bi-component Mn3O4–MnO2 nanorods and enhanced catalytic properties

Bi-component Mn₃O₄–MnO₂ nanorods with lengths of up to 30 μm are synthesized using a simple hydrothermal method in the absence of templates. Samples were characterized by FE-SEM, HR-TEM, XRD, XPS, and N₂ adsorption–desorption. The results indicate that the Mn₃O₄–MnO₂ and Mn₅O₈ samples with various morphologies can be easily obtained via modulating Cl⁻ ions and glucose contents. Compared with that of the Mn₅O₈ samples, the bi-component Mn₃O₄–MnO₂ nanorods exhibited higher catalytic properties for oxidative decomposition of MB owing to its adjustable valence state and oxygen content.