bluuebunny/crossref_metadata_2025_split huggingface dataset:
Patterning Smectic Liquid Crystals for OFETs at Low Temperature
Authors: Zou Cheng , Yanahashi Naoto , Wu Yuchen , Wang Jingxia , Zhang Cuihong , Xiong Guirong , Yang Huai , Jiang Lei , Ikeda Tomiki 
Published: January 2019

AbstractThe preparation of regular microstructures with liquid crystalline materials for organic field effect transistors (OFETs) is an attractive but challenging issue. However, it is usually limited by the difficulty of forming large‐area single crystals aligned in a desirable direction. Herein, several terthiophene (TTP) smectic liquid crystals such as 8‐TTP‐8 and 12‐TTP‐11OH are patterned into highly crystalline microstripes by a sandwich system through a dewetting method. Morphology and orientation of the microstripes strongly depend on preparation temperature. Microstripes prepared below crystalline temperature are uniform, well‐ordered, and show high field effect transistor (FET) mobility. Meanwhile, π–π stacking direction of the TTP backbone is perpendicular to the microstripe and the molecules stack in layer structure, standing up on the SiO2/Si substrate, which would provide an effective pathway for p‐type charge transport. However, higher preparation temperatures at liquid crystalline or isotropic liquid range induce many defects in the crystal formation process and cause incline of the unit cell, thus leading to a sharp decrease in FET mobility. A possible mechanism of molecular stacking at different temperature range is proposed. This strategy promised to provide a new opportunity for the high cost‐efficiency fabrication of OFETs.
Hierarchical Metamaterials for Multispectral Camouflage of Infrared and Microwaves
Authors: Kim Taehwan , Bae Ji‐Yeul , Lee Namkyu , Cho Hyung Hee 
Published: January 2019

AbstractCamouflage is an emerging application of metamaterials owing to their exotic electromagnetic radiative properties. Based on the use of a selective emitter and an absorber as the metamaterials, most reported articles have suggested the use of single‐band camouflage, however, multispectral camouflage is a challenging issue owing to a difference of several orders of magnitude in the unit cell structure. Herein, hierarchical metamaterials (HMMs) for multispectral signal control when dissipating the absorbed energy of microwaves through the selective emission of infrared (IR) waves from the unit cell structure of the HMM are demonstrated. Integrating an IR selective emitter (IRE) with a microwave selective absorber, multispectral signal control with the large‐sized unit cell structures of up to 10 cm are realized. With an IRE, the emissive power from the HMM toward 5–8 µm is 1570% higher than the Au surface, which is preventing the occurrence of thermal instability. Furthermore, we determine that the signature levels of targeted IR waves (8–12 µm) and microwaves (2.5–3.8 cm) are reduced by up to 95% and 99%, respectively, when applying the HMM.
Carbonized‐MOF as a Sulfur Host for Aluminum–Sulfur Batteries with Enhanced Capacity and Cycling Life
Authors: Guo Yue , Jin Hongchang , Qi Zhikai , Hu Zhiqiu , Ji Hengxing , Wan Li‐Jun 
Published: January 2019

AbstractThe rechargeable aluminum–sulfur (Al–S) battery is a promising next generation electrochemical energy storage system owing to its high theoretical capacity of 1672 mAh g−1 and in combining low‐cost and naturally abundant elements, Al and S. However, to date, its poor reversibility and low lifespan have limited its practical application. In this paper, a composite cathode is reported for Al–S batteries based on S anchored on a carbonized HKUST‐1 matrix (S@HKUST‐1‐C). The S@HKUST‐1‐C composite maintains a reversible capacity of 600 mAh g−1 at the 75th cycle and a reversible capacity of 460 mAh g−1 at the 500th cycle under a current density of 1 A g−1, with a Coulombic efficiency of around 95%. X‐ray diffraction and Auger spectrum results reveal that the Cu in HKUST‐1 forms S–Cu ionic clusters. This serves to facilitate the electrochemical reaction and improve the reversibility of S during charge/discharge. Additionally, Cu increases the electron conductivity at the carbon matrix/S interface to significantly decrease the kinetic barrier for the conversion of sulfur species during battery operation.
Slow Hot‐Carrier Cooling in Halide Perovskites: Prospects for Hot‐Carrier Solar Cells
Authors: Li Mingjie , Fu Jianhui , Xu Qiang , Sum Tze Chien 
Published: January 2019

AbstractRapid hot‐carrier cooling is a major loss channel in solar cells. Thermodynamic calculations reveal a 66% solar conversion efficiency for single junction cells (under 1 sun illumination) if these hot carriers are harvested before cooling to the lattice temperature. A reduced hot‐carrier cooling rate for efficient extraction is a key enabler to this disruptive technology. Recently, halide perovskites emerge as promising candidates with favorable hot‐carrier properties: slow hot‐carrier cooling lifetimes several orders of magnitude longer than conventional solar cell absorbers, long‐range hot‐carrier transport (up to ≈600 nm), and highly efficient hot‐carrier extraction (up to ≈83%). This review presents the developmental milestones, distills the complex photophysical findings, and highlights the challenges and opportunities in this emerging field. A developmental toolbox for engineering the slow hot‐carrier cooling properties in halide perovskites and prospects for perovskite hot‐carrier solar cells are also discussed.
Perovskite Photovoltaics: The Significant Role of Ligands in Film Formation, Passivation, and Stability
Authors: Zhang Hong , Nazeeruddin Mohammad Khaja , Choy Wallace C. H. 
Published: January 2019

AbstractDue to their outstanding optoelectronic properties, metal halide perovskites have been intensively studied in recent years. The latest certificated efficiency of 23.3% recently achieved in perovskite solar cells (PVSCs) enables them to be used as a very promising candidate for next‐generation photovoltaics. The morphology, defect density, and water resistance of perovskite films have an enormous impact on the performance and stability of PVSCs. Ligands, with coordinating capability, have been widely developed to improve the quality and stability of perovskite materials significantly. In the first section of this review, the role of ligands in fabricating perovskite films by different methods (one‐step, two‐step, and postdeposition treatment) is discussed. In the second section, the progress on ligand‐passivated perovskites via post‐treatment, in situ passivation during perovskite formation, and modifying the substrates before perovskite formation is reviewed. In the third section, a discussion of ligand‐stabilized perovskite films from the perspectives of crystal crosslinking, dimensionality engineering, and interfacial modification is presented. Finally, a summary and an outlook are given.
Interfacial Modification in Organic and Perovskite Solar Cells
Authors: Bi Shiqing , Leng Xuanye , Li Yanxun , Zheng Zhong , Zhang Xuning , Zhang Yuan , Zhou Huiqiong 
Published: January 2019

AbstractOrganic bulk heterojunction solar cells (OSCs) and hybrid halide perovskite solar cells (PSCs) are two promising photovoltaic techniques for next‐generation energy conversion devices. The rapid increase in the power conversion efficiency (PCE) in OSCs and PSCs has profited from synergetic progresses in rational material synthesis for photoactive layers, device processing, and interface engineering. Interface properties in these two types of devices play a critical role in dictating the processes of charge extraction, surface trap passivation, and interfacial recombination. Therefore, there have been great efforts directed to improving the solar cell performance and device stability in terms of interface modification. Here, recent progress in interfacial doping with biopolymers and ionic salts to modulate the cathode interface properties in OSCs is reviewed. For the anode interface modification, recent strategies of improving the surface properties in widely used PEDOT:PSS for narrowband OSCs or replacing it by novel organic conjugated materials will be touched upon. Several recent approaches are also in focus to deal with interfacial traps and surface passivation in emerging PSCs. Finally, the current challenges and possible directions for the efforts toward further boosts of PCEs and stability via interface engineering are discussed.
A New Class of Materials: Sequence‐Defined Macromolecules and Their Emerging Applications
Authors: Meier Michael A. R. , Barner‐Kowollik Christopher 
Published: January 2019

AbstractEmerging applications of a new class of materials, sequence‐defined macromolecules, are explored. Such molecularly highly defined macromolecules require stringent synthesis and purification procedures, yet offer unprecedented application possibilities. The first examples of molecular data storage and related technologies are already starting to emerge today. From a more fundamental point of view, such macromolecules offer a unique opportunity to determine quantitative structure–property relationships (QSPR), which critically aids in designing materials with applications ranging from catalysis to artificial enzymes.
Stretchable Conductive Polymers and Composites Based on PEDOT and PEDOT:PSS
Authors: Kayser Laure V. , Lipomi Darren J. 
Published: January 2019

AbstractThe conductive polymer poly(3,4‐ethylenedioxythiophene) (PEDOT), and especially its complex with poly(styrene sulfonate) (PEDOT:PSS), is perhaps the most well‐known example of an organic conductor. It is highly conductive, largely transmissive to light, processible in water, and highly flexible. Much recent work on this ubiquitous material has been devoted to increasing its deformability beyond flexibility—a characteristic possessed by any material that is sufficiently thin—toward stretchability, a characteristic that requires engineering of the structure at the molecular‐ or nanoscale. Stretchability is the enabling characteristic of a range of applications envisioned for PEDOT in energy and healthcare, such as wearable, implantable, and large‐area electronic devices. High degrees of mechanical deformability allow intimate contact with biological tissues and solution‐processable printing techniques (e.g., roll‐to‐roll printing). PEDOT:PSS, however, is only stretchable up to around 10%. Here, the strategies that have been reported to enhance the stretchability of conductive polymers and composites based on PEDOT and PEDOT:PSS are highlighted. These strategies include blending with plasticizers or polymers, deposition on elastomers, formation of fibers and gels, and the use of intrinsically stretchable scaffolds for the polymerization of PEDOT.
Linear and Nonlinear Optical Properties of Few‐Layer Exfoliated SnSe Nanosheets
Authors: Ye Yuting , Xian Yuehui , Cai Jiawen , Lu Kaicheng , Liu Zhengzheng , Shi Tongchao , Du Juan , Leng Yuxin , Wei Rongfei , Wang Weiqi , Liu Xiaofeng , Bi Gang , Qiu Jianrong 
Published: January 2019

AbstractMonochalcogenides of group IV elements have been considered as phosphorene analogs due to their similar crystal and electronic structure. Here, few‐layer SnSe nanosheets are synthesized by a sonication‐assisted liquid phase exfoliation process and their linear and nonlinear optical properties are examined. The as‐exfoliated few‐layer (FL) SnSe demonstrates layer thickness from 2 to 10 nm and lateral size of 150 nm with high crystallinity. Optical measurement confirms the layer‐number dependent bandgap, which is also corroborated by first‐principle calculation. In addition, the FL SnSe shows a transition from saturable absorption to reverse saturable absorption with the increase of pumping power, and the nonlinear absorption is characterized by an ultrafast response time of picosecond scale. The nonlinear optical response in FL SnSe could be explained by defect‐involved recombination of photogenerated carriers as well as the Auger scattering process, which is further enhanced by structural two‐dimensionality.
Ultrathin Metal Films as the Transparent Electrode in ITO‐Free Organic Optoelectronic Devices
Authors: Bi Yan‐Gang , Liu Yue‐Feng , Zhang Xu‐Lin , Yin Da , Wang Wen‐Quan , Feng Jing , Sun Hong‐Bo 
Published: January 2019

AbstractTransparent conductive electrodes, as transmission windows of photons and electrons, play important roles in high‐performance organic optoelectronic devices. The replacement of widely used indium tin oxide (ITO) electrodes has been attempted due to the increasing cost and intrinsically brittle characteristics of ITO. Ultrathin metal films, with excellent optoelectrical features, high flexibility, and sufficient mechanical stability, have been considered a potential candidate for the use as transparent conductive electrodes. However, ultrathin metal films follow the Volmer–Weber mechanism, resulting in a rough and discontinuous morphology with poor optoelectrical properties due to the bad adhesion to substrates. This review summarizes the progress in strategies for preparing ultrathin and ultrasmooth metal films with superior transmittance and conductivity by successfully suppressing the Volmer–Weber mechanism. The electrical and optical performances of the ultrathin metal films based on improved nucleation processes, as well as applications in ITO‐free organic optoelectronic devices, are also described and discussed in detail.
Directional Modulation of Fluorescence by Nanowire‐Based Optical Traveling Wave Antennas
Authors: Wang Yilin , Li Chao , Duan Gaoyan , Wang Lulu , Yu Li 
Published: January 2019

AbstractPlasmonic optical antennas can direct light from quantum emitters and improve nanophotonics device efficiency. In this study, composite structures with V‐shaped Ag nanowires (V‐Ag NWs) and quantum dots (QDs) are designed and fabricated. V‐Ag NWs serving as optical traveling wave antennas (TWAs) are employed for QD fluorescence emission direction control. The modulated emission directionality is achieved up to 11.8 dB, and the azimuthal angle half‐power bandwidth is as narrow as 35°. The azimuthal radiation is effectively tuned from 0° to over 40° by changing the bending angles of the structures. Finite‐difference time‐domain and Green's function methods are used to analyze the far field radiation patterns that are in good agreement with the experiment measurements. TWAs are easy to fabricate and integrate with optical waveguide. Thus, they are excellent tools for realizing unidirectional fluorescence emission and are potentially applicable in integrated plasmonics and nanophotonics devices.
Narrow‐Band Green‐Emitting Sr2MgAl22O36:Mn2+ Phosphors with Superior Thermal Stability and Wide Color Gamut for Backlighting Display Applications
Authors: Zhu Yingli , Liang Yujun , Liu Shiqi , Li Haoran , Chen Jiahui 
Published: January 2019

AbstractThe narrow‐band emitting phosphors have been extensively investigated in recent years, with the expectation that a wide color gamut of phosphor‐converted backlighting device could be fabricated. Due to the weak electric–phonon interaction and low structural relaxation caused by the high rigid crystal structure and symmetric coordination environment, Sr2MgAl22O36:Mn2+ (SMAO:Mn2+) shows a narrow full‐width at half‐maximum of 26 nm, a high color purity of 81.5%, and a low thermal quenching (82% at 473 K of the initial intensity at 298 K). Using K2SiF6:Mn4+ as the red phosphor, SMAO:Mn2+ as the green one, and GaN‐based chip as the blue component, the white light‐emitting diode exhibits a National Television Standard Committee value of 127%. All the results demonstrate that the SMAO:Mn2+ phosphor has a promising application in the field of advanced wide‐color‐gamut backlight display, and the establishment of the relationships between the narrow‐band emission and crystal structure can also be applied to design other novel narrow‐band phosphors for backlighting technologies.
Ternary Exciplexes for High Efficiency Organic Light‐Emitting Diodes by Self‐Energy Transfer
Authors: Jeon Sang Kyu , Jang Ho Jin , Lee Jun Yeob 
Published: January 2019

AbstractTernary exciplexes with an external quantum efficiency of 17.5% are developed by mixing a p‐type donor material, an n‐type acceptor material, and a donor–acceptor type material together. In the ternary mixture, the n‐type donor generates exciplexes with the p‐type donor and the donor–acceptor type material at the same time. Two different exciplexes with dissimilar emission wavelengths are formed and the emission of the high‐energy exciplex is transferred to the low‐energy exciplex by energy transfer. The high‐energy exciplex and low‐energy exciplex work as a host and dopant in the emitting layer, respectively. The internal exciplex‐to‐exciplex energy transfer induces efficient emission of the low‐energy exciplex, resulting in high efficiency of 17.5% in the exciplex device. This is the first demonstration of self‐energy transfer in the exciplex and the efficiency of the ternary exciplexes is one of the best quantum efficiencies achieved in the exciplex organic light‐emitting diodes.
Discovery of New Narrow‐Band Phosphors with the UCr4C4‐Related Type Structure by Alkali Cation Effect
Authors: Zhao Ming , Zhou Yayun , Molokeev Maxim S. , Zhang Qinyuan , Liu Quanlin , Xia Zhiguo 
Published: January 2019

AbstractNarrow‐band luminescence materials used in white light‐emitting diodes (WLEDs) have demonstrated a great potential to increase the maximum accessible color gamut, improve the color rendition, or enhance the visual luminous efficacy for illumination and display devices. So far, the discovery of narrow‐band rare earth doped phosphors for emerging applications remains challenging owing to the limited systems in use and the broadening effect of 4f–5d transition. Here, two narrow‐band cyan‐emitting phosphors with the UCr4C4‐related type structure, RbNa2K(Li3SiO4)4:Eu2+ (RNKLSO:Eu2+) and CsNa2K(Li3SiO4)4:Eu2+ (CNKLSO:Eu2+), are reported. The narrow‐band emission results from the highly condensed network and a cube‐like site for the activator (Eu2+). The emission peak assignments are investigated, and the variations of luminescence behavior with compositional changes of alkali cations are elaborated in detail. RNKLSO:8% Eu2+ (95%@250 °C of the integrated emission intensity at 25 °C) shows better thermal stability than that of CNKLSO:8% Eu2+ (79%@250 °C), which can be explained by the thermally activated crossover process represented in the configurational coordinate diagram. The optical properties of the as‐fabricated WLEDs are studied and demonstrate potential with tunable properties for the full spectrum phosphor‐converted LEDs. These findings in UCr4C4‐type phases help shedding light on new avenues for fabricating new and totally unexpected narrow‐emitting phosphors with versatile applications.
A Copper (II) Acetate Mediated Oxidative‐Coupling of Styrenes and Ethers Through an Unactivated C(sp3)−H Bond Functionalization
Authors: Yan Zhan , Wang Nai‐Xing , Gao Xue‐Wang , Li Jian‐Li , Wu Yue‐Hua , Zhang Tong , Chen Shi‐Lu , Xing Yalan 
Published: January 2019

AbstractA Copper (II) Acetate Mediated Oxidative Coupling of Styrenes and Ethers Through an Unactivated C(sp3)−H Bond FunctionalizationA functionalization of unactivated C(sp3)‐H bond of ethers with styrenes was described. This C−C bond formation has been developed using t‐butyl hydroperoxide (TBHP) as a radical initiator and DBU as an additive agent. Typical ethers underwent a free‐radical addition of styrenes to give direct difunctionalization products with excellent regioselectivity and efficiency. This reaction features good yields and functional group compatibility with simple operation and mild conditions. A plausible reaction mechanism has been proposed. DFT simulation and theory calculation also provided important evidence for the proposed free‐radical mechanism.magnified image
Applications of Thermal Activation, Ball‐milling and Aqueous Medium in Stereoselective Michael Addition of Nitromethane to Enynones Catalyzed by Chiral Squaramides
Authors: Ignatiuk Żaneta A. , Janicki Mikołaj J. , Góra Robert W. , Konieczny Krzysztof , Kowalczyk Rafał 
Published: January 2019

AbstractStereoselective addition of nitromethane to conjugated en‐ynones was performed through the application of chiral squaramides. Three non‐classical approaches to promote the addition reaction were tested, including activation of the nucleophile by inorganic base in a biphasic aqueous system, thermal activation, and ball‐milling. Hydrogen‐bonding catalysis was effective in all these methods, providing 1,4‐addition products in high yields and stereoselectivities of up to 98% requiring 1–5 mol% of Cinchona alkaloid squaramide.magnified image
Poly(1,4‐di(2‐thienyl))benzene Facilitating Complete Light‐Driven Water Splitting under Visible Light at High pH
Authors: Oka Kouki , Noguchi Kanako , Suga Takeo , Nishide Hiroyuki , Winther‐Jensen Bjorn 
Published: January 2019

AbstractThe recent discovery that metal‐free polyterthiophene (PTTh) prepared by iodine‐vapor‐assisted polymerization (IVP) can catalyze the hydrogen evolution reaction (HER) when illuminated, and this light‐enhanced electrolysis expresses a non‐Nernstian relation with pH, provides the foundation for further improvement of the photovoltage of the reaction by engineering the band structure of the light‐absorbing polymer. Deviating from an all‐thiophene backbone, using poly(1,4‐di(2‐thienyl))benzene (PDTB) lowers the highest occupied molecular orbital level by ≈0.3 eV compared with polythiophene, and PDTB simultaneously maintains the photoelectrocatalytic properties without an all‐thiophene backbone, resulting in very high conversion rate of 600 mmol(H2) h−1 g−1 at 0 V versus the reversible hydrogen electrode (RHE) at pH 11. PDTB shows the same non‐Nernstian behavior as PTTh with increasing onset potential (versus RHE) at higher pH, and the open circuit potential on PDTB under visible light reaches 1.4 V versus RHE at pH 12. The PDTB photocathode thus produces a photovoltage above the theoretical potential for the complete water‐splitting (1.229 V) and is indeed able to produce hydrogen in a one‐photon‐per‐electron light‐driven water splitting setup with MnOx as the anode at a rate of 6.4 mmol h−1 gPDTB−1.
Synthesis of Crosslinked Chiral Polysiloxanes of Cinchona Alkaloid Derivatives and their Applications in Asymmetric Catalysis
Authors: Kumpuga Bahati Thom , Itsuno Shinichi 
Published: January 2019

AbstractCrosslinked chiral polysiloxanes containing cinchona alkaloid derivatives were synthesized from poly(methylhydrosiloxane) by hydrosilylation reaction. The C3‐vinyl group of cinchona alkaloid derivatives were easily hydrosilylated with Si−H functional groups of poly(methylhydrosiloxane) by using Pt catalyst. The reaction between cinchona alkaloid dimers and poly(methylhydrosiloxane) and afforded the crosslinked chiral polysiloxanes. Partial hydrolysis of Si−H bonds with Pt catalyst during reaction resulted in a formation of extra crosslinkages of chiral polysiloxanes. Mixed solvent (toluene and DMF) system was employed for a successful immobilization of C6′−OH free cinchona alkaloid derivatives into poly(methylhydrosiloxane). Both cinchona alkaloid C9‐ester and C9‐urethane derivatives were incorporated into poly(methylhydrosiloxane) through Si−C bond. The resulted crosslinked chiral polysiloxanes were insoluble in common organic solvents. Their catalytic performance was evaluated in asymmetric Michael addition reactions. The chiral polysiloxanes of cinchona alkaloid having C6′−OH showed higher enantioselectivities (up to 99% ee) with sufficient catalytic activities in the Michael addition reactions. The chiral polysiloxanes were easily recovered by filtration or centrifugation method and could be reused for several times without losing their catalytic performance.