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Note: The papers published below will continue to be available from this page until they are assigned to an issue. To see an article, click its [PDF] link. To review many abstracts, check the boxes to the left of the titles you want, and click the 'Selected articles' button. To see one abstract at a time, click its [Abstract] link.
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Interface Energetics and Engineering of Organic Heterostructures in Organic Photovoltaic Cells

Yan-Qing Li, Qian-Kun Wang, Qing-Dong Ou & Jian-Xin Tang*
Accept: 2015-11-18
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The reliable information about interface energetics of organic materials, especially the energy level alignment at organic heterostructures is of pronounced importance for unraveling the photon harvesting and charge separation process in organic photovoltaic (OPV) cells. This article provides an overview of interface energetics at typical planar and mixed donor-acceptor heterostructures, perovskite/organic hybrid interfaces, and their contact interfaces with charge collection layers. The substrate effect on energy level offsets at organic heterostructures and the processes that control and limit the OPV operation is presented. Recent efforts on interface engineering with electrical doping are also discussed.
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  Organolead Trihalide Perovskite Materials for Efficient Light Emitting Diodes

Ming Peng1, Wen Wen1, Si Chen1, Buxin Chen1, Kai Yan1, Hsienwei Hu1, Bin Dong1, Xue Gao1, Xiao Yu1, and Dechun Zou1, 2, *
Accept: 2015-11-18
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Organolead trihalide perovskite materials have been attracting increasing attention due to their promising role in solid solar cells. Several advantages make them potential candidates for optoelectronics: 1) solution- or/and vapor-processed preparation at low temperature; 2) tunable optical bandgap, wide absorption spectrum but narrow photoluminescence peaks; 3) long carrier life time, large diffusion length and high charge mobility; 4) various nanostructures via tuning capping agents and solvents. In this review, we summarize recent attempts toward efficient LEDs based on organolead trihalide perovskite materials. The strategies of materials science, device design, interface engineering are highlighted. Recent development and future perspectives are summarized for practical perovskite light technologies.

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Dustin Chen, Jiajie Liang & Qibing Pei
Accept: 2015-11-18
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Transparent conductive electrodes play a significant role in the fabrication and development of optoelectronic devices. As next generation optoelectronic devices trend towards mobile and wearable devices, the added attribute of flexibility or stretchability for these electrodes becomes increasingly important. However, mechanical requirements aside, transparent conductive electrodes must still retain high transparency and conductivity, with the metrics for these parameters being compared to the standard, indium tin oxide. In the search to replace indium tin oxide, two materials that have risen to the forefront are carbon nanotues and silver nanowires due to their high transparency, conductivity, mechanical compliance, and ease of fabrication. This review highlights recent innovations made by our group in electrodes utilizing carbon nanotubes and silver nanowires, in addition to the use of these electrodes in discrete devices and integrated systems.

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A Self-Catalytic Role of Methanol in PNP-Ru Pincer Complex Catalysed Dehydrogenation

Yuan-Ye Jiang1,2, Zheng-Yang Xu,2 Hai-Zhu Yu1* & Yao Fu2*
Accept: 2015-11-18
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Extracting hydrogen from methanol is a safe and cost-efficient strategy for fuel supply. This process was realized recently at a mild condition with excellent efficiency by ruthenium pincer catalysts. Despite of the experimental success, the associated mechanism remains under debate. With the aid of density functional theory (DFT) calculations, an updated and self-consistent mechanism which involves MeOH-catalysed dehydrogenation of ruthenium hydride intermediate and pre-protonation of the pincer ligand was present herein. This mechanism is kinetically favoured over the previously-proposed water- or for-mic-acid-participated ones and more consistent with the optimal experimental condition where strong base and neat methanol solvent are used.
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Solution-processable graphenes by covalent functionalization of graphene oxide with polymeric monoamines

Jing Wang,1 Ke Feng,1* Nan Xie,2 Zhi-Jun Li,1 Qing-Yuan Meng,1 Bin Chen,1 Chen-Ho Tung1 & Li-Zhu Wu1*
Accept: 2015-11-18
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We develop here a simple wet chemistry to prepare covalent functionalized graphenes (FGs) through epoxide aminolysis espe-cially under alkaline aqueous condition. Remarkably, a series of typical monoamines, such as industrial Huntsman Jeffamine® M-2070 and M-2005 polymer with hydrophilic or hydrophobic polyetheramine chains, positively-charged 2-amino-N,N,N-trimethylpropanaminium, negatively-charged sulfanilic acid, even oligopeptide sequence, can be effectively grafted on the platelets of graphene oxide precursor with covalent functionalization and partially reduced features. This strategy provides the researchers a facile and convenient approach to design and synthesize solution processable, biocompatible and functionalized graphenes for the potent applications in electronic inks, drug carriers and biomedicines. Expansion of the current study is actively undergoing in our laboratory.

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Imaging Cellular Distribution of Fluorescent Supermolecular Nanofibers

WANG JingYu1, ZHENG Jing2, CAI YanBin3, ZHENG JinXin2, GAO Jie3*, GONG QingQiu2* & YANG ZhiMou3*
Accept: 2015-11-18
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In this study, we use the 4-nitro-2,1,3-benzoxadiazole (NBD) as an aromatic capping group for a peptide to construct the su-pramolecular nanofibers. Taking the advantage of the fluorescence property of NBD, we can directly observe the cellular dis-tribution of the self-assembled nanofibers. We find that the distributions of the nanofibers of NBD-FFETIGGY are different in four mammalian cells and two plant cells. The nanofibers are mainly located at the surface of two mammalian cells and one plant cell, while in the intracellular space of other cells. Different distributions of nanofibers lead to different protein binding patterns of the nanofibers in two different cell lines. We believe thata useful and versatile platform has been offered to the image cellular distribution of nanofibers, whichcan provide useful information to the biological functions of the self-assembled nanostructures.
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Visualization of α1-Adrenergic Receptors with Phenylpiperazine-based Fluorescent Probes

Yuxing Lin, Wenhua Li, Qinying Yu, Xinyang Zhou, Wei Zhang, Lupei Du, Minyong Li
Accept: 2015-10-12
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Several novel fluorescent probes targeting α1-adrenergic receptors were well designed and synthesized by conjugating phenylpiperazine pharmacophore with coumarin and fluorescein fluorophores. These compounds showed suitable fluorescence property, high receptor affinity, and low cytotoxicity. Moreover, the cell imaging results displayed that these probes can be effective tools for the real-time detection of ligand−receptor interactions, as well as the visualization and location of α1-adrenergic receptors in living cells.

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Biosensing strategy based on photocurrent quenching of quantum dots via energy resonance absorption

WEN GuangMing, WANG Peng, TU WenWen, LEI JianPing & JU HuangXian
Accept: 2015-02-06
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A new concept of energy resonance absorption for photocurrent quenching was proposed using a system of quantum dots (QDs) and the matched dye. The QDs were used as the photocurrent producer, and the dye had an absorption band overlapped with that of the QDs, which led to the resonance absorption of the excitation energy and thus decreased the photocurrent of QDs. By using porphyrin and fluorscein isothiocyanate isomer I as the resonance absorption dyes, the proposed mechanism was proved by UV/vis spectra, photoluminescence spectra and photocurrent-to-wavelength response, respectively. The interaction of the absorption-matched dye with biomolecule could be conveniently used to introduce it into the photocurrent quenching system, leading to a simple switch-off biosensing method for detection of the biomolecule. As example, a label-free method was proposed for photoelectrochemical detection of target DNA. This method showed a detection range from 6.0 to 600 nM with a detection limit of 2.5 nM. The result demonstrated that the photocurrent quenching via energy resonance absorption not only contributed to the theoretical study of photoelectrochemistry, but also provided a universal tool for photoelectrochemical biosensing.
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The First Enantioselective Total Synthesis of (+)-Preussin B and an Improved Synthesis of (+)-Preussin By Step-economical Methods

HUANG Pei-Qiang,* GENG Hui, TIAN Yong-Song, PENG Qiu-Ran, and XIAO Kai-Jiong
Accept: 2014-11-18
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The first enantioselective total synthesis of (+)-preussin B and an improved synthesis of the antifungal alkaloid (+)-preussin are described. Our approach relied on the four step-economical synthetic methods developed in our laboratory: (1) the cis-diastereoselective reductive dehydroxylation of hemiaminals; (2) the direct amide/ lactam reductive alkylation; (3) the one-pot N,O-bisdebenzylation–N-methylation; and (4) the one-step synthesis of malimide from malic acid. Both total syntheses are quite concise, which have been achieved in six steps, and give overall yields of 25.7% and 27.6%, respectively.

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Fully degradable brush polymers with polycarbonate backbones and polylactide side chains

Jie Liu, Weimin Ren, & Xiaobing Lu*
Accept: 2014-11-12
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Novel, fully degradable brush polymers with polycarbonate backbones and polylactide side chains were prepared by a three-step reaction that included the terpolymerization of cyclohexene oxide (CHO) and benzyl glycidyl ether (BGE) with CO2, hydrogenation of the resultant terpolymers to afford the terpolymers with 1,2-glycerol carbonate units and the 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) mediated ring-opening polymerization of lactide on the polycarbonate backbone. The brush copolymer bearing polylactide (PLA) chains from racemic lactide (rac-LA) has a single glass-transition temperature of 58.5 °C, whereas the copolymers with (L)-PLA side chains exhibited a melting enthalpy at 135.8 °C with ∆Hm=25.04 J/g and were further shown by a WAXD study to be a typical semicrystalline polymer with sharp diffraction peaks at 2θ values of 16.7° and 18.9°.
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Side-chain engineering of high-efficiency conjugated polymer photovoltaic materials

Zhi-Guo Zhang1 & Yongfang Li1,2*
Accept: 2014-11-11
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Received September 1, 2014; accepted September 19, 2014 In recent years, conjugated polymers have attracted great attention in the application as photovoltaic donor materials in polymer solar cells (PSCs). Broad absorption, lower-energy bandgap, higher hole mobility, relatively lower HOMO energy levels, and higher solubility are important for the conjugated polymer donor materials to achieve high photovoltaic performance. Side-chain engineering plays a very important role in optimizing the physicochemical properties of the conjugated polymers. In this article, we review recent progress on the side-chain engineering of conjugated polymer donor materials, including the optimization of flexible side-chains for balancing solubility and intermolecular packing (aggregation), electron-withdrawing substituents for lowering HOMO energy levels, and two-dimension (2D)-conjugated polymers with conjugated side-chains for broadening absorption and enhancing hole mobility. After the molecular structural optimization by side-chain engineering, the 2D-conjugated polymers based on benzodithiophene units demonstrated the best photovoltaic performance, with power-conversion efficiency higher than 9%.
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Loop formation and stability of self-avoiding polymer chains

Wancheng Yu, Kaifu Luo
Accept: 2014-09-29
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Using 3-dimensional Langevin dynamics simulations, we investigated the dynamics of loop formation of chains with excluded volume interactions, and the stability of the formed loop. The mean looping time τl scales with chain length N and corresponding scaling exponent α increases linearly with the capture radius scaled by the Kuhn length a/l due to the effect of finite chain length. We also showed that the probability density function of the loop time is well fitted by a single exponential. Finally, we found that the mean unlooping time τu hardly depends on chain length N for a given a/l and that the stability of a formed loop is enhanced with increasing a/l.

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The effect of interfacial diffusion on device performance of polymer solar cells: A quantitative view by active-layer doping

NIAN Li, ZHOU JiaDong, ZENG Kai, WU XiaoYan, LIU LinLin,* XIE ZengQi,* HUANG Fei, & MA YuGuang*
Accept: 2014-09-29
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The diffusion of constituent materials at interfaces is one of the key factors for device performance and stability. In this work, the effect of interfacial diffusion of a classic interfacial material PFN on device performance of polymer solar cells was studied quantitatively by doping PFN into active layer based on P3HT:PC61BM blend. The PCEs of devices with 550 ppm PFN decrease to half compared to those of the control devices without PFN, which are mainly attributed to the decrease of short-circuit current (Jsc) and fill factor (FF). Advanced analyses of equivalent circuit, absorption spectra, and atomic force microscopy indicates that the presence of PFN in the active layer increases the leakage current, decreases the aggregation of P3HT, and reduces the phase separation. This research reveals the physical mechanism of interfacial diffusion in device performance and provides a basis for further improving the performance and stability of PSCs.
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Low band-gap benzodithiophene-thienothiophenecopolymers: The effect of dual two-dimensional substitutions on optoelectronic properties

LIUZhulin, SUN Jiangman, ZHUYongxiang,LIU Peng, ZHANG Lianjie,* CHEN Junwu,* HUANG Fei,&CAOYong
Accept: 2014-09-29
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Two new conjugated copolymers, PBDT-T6-TTF and PBDT-T12-TTF, were derived from a novel 4-fluorobenzoyl thienothi-ophene (TTF). In addition, two types of benzodithiophene (BDT) units with 2,3-dihexylthienyl (T6) and 2,3-didodecylthienyl (T12) substituents, respectively, were successfully synthesized. The effect of the dual two-dimensional (2D) substitutions of the building blocks upon the optoelectronic properties of the polymers was investigated. Generally, the two polymers exhibited good solubility and broad absorption, showing similar optical band gaps of ~1.53 eV. However, PBDT-T6-TTF with its shorter alkyl chain length possessed a larger extinction coefficient in thin solid film. The highest occupied molecular orbital (HOMO) level of PBDT-T6-TTF was located at –5.38 eV while that of PBDT-T12-TTF was at –5.51 eV. In space charge-limited-current (SCLC) measurement, PBDT-T6-TTF and PBDT-T12-TTF displayed respective hole mobilities of 3.0×10–4 and 1.6×10–5 cm2/(V s). In polymer solar cells, PBDT-T6-TTF and PBDT-T12-TTF showed respective power conversion efficiencies (PCEs) of 2.86% and 1.67%. When 1,8-diiodooctane (DIO) was used as the solvent additive, the PCE of PBDT-T6-TTF was remarkably elevated to 4.85%, but the use of DIO for the PBDT-T12-TTF-blend film resulted in a lower PCE of 0.91%. Atomic force microscopy (AFM) indicated that the superior efficiency of PBDT-T6-TTF with 3% DIO (v/v) should be related to the better continuous phase separation of the blend film. Nevertheless, the morphology of the PBDT-T12-TTF deteriorated when the 3% DIO (v/v) was added. Our results suggest that the alkyl-chain length on the 2D BDT units play an important role in determining the optoelectronic properties of dual 2D BDT-TT-based polymers.
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A new oligobenzodithiophene end-capped with 3-ethyl-rhodanine groups for organic solar cells with highopen-circuit voltage

NI Wang, LI MiaoMiao, WAN XiangJian, ZUO Yi, KAN Bin, FENG HuanRan, ZHANG Qi-an, CHEN YongSheng
Accept: 2014-09-29
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A new solution-processable small-molecule donor material, named DRBDT3, comprised of oligobenzo[1,2-b:4,5-b'] dithiophene as the backbone and 3-ethyl-rhodanine as the end-capped group has been designed and synthesized for application in organic photovoltaic cells. The oligobenzodithiophene derivative exhibits an absorption band from 300 to 640 nm. The film of DRBDT3 shows highly long-range ordering assembly and high mobility of 1.21×10-4 cm2 V-1 s-1. The new molecule shows a deep highest-occupied molecular orbital energy level. The device based on DRBDT3 as the donor and PC71BM as the acceptor exhibits a power conversion efficiency of 4.09% with a high open-circuit voltage of 0.99 V under AM.1.5G illumination (100 mWcm-2).
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Alcohol/water-soluble porphyrins as cathode interlayers in high- performance polymer solar cells

JIA Tao, ZHOU WeiLong, LI FengHong, GAO YaJun, WANG Lu, HAN JianXiong, ZHANG JingYing, & WANG Yue
Accept: 2014-09-29
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Three alcohol/water-soluble porphyrins (Zn-TPyPMeI: zinc(II) meso-tetra(N-methyl-4-pyridyl) porphyrin tetra-iodide, Zn-TPyPAdBr: zinc(II) meso-tetra[1-(1- adamantylmethyl ketone)-4-pyridyl] porphyrin tetra-bromide and MnCl-TPyPAdBr: manganese(III) meso-tetra[1-(1-adamantylmethyl ketone)-4-pyridyl] porphyrin tetra-bromide) were employed as cathode in-terlayers to fabricate polymer solar cells (PSCs). The PC71BM ([6,6]-phenyl C71 butyric acid methyl ester) and PCDTBT (poly[N-9´´-hepta-decanyl-2,7-carbazole-alt-5,5-(4´,7´-di-2-thienyl-2´,1´,3´-benzothiadiazole)])-blend films were used as active layers in PSCs. The PSCs with alcohol/water-soluble porphyrins interlayer showed obviously higher power conversion ef-ficiency (PCE) than those without interlayers. The highest PCE, 6.86%, was achieved for the device with MnCl-TPyPAdBr as an interlayer. Ultraviolet photoemission spectroscopic (UPS), carrier mobility, atomic force microscopy (AFM) and contact angle (θ) characterizations demonstrated that the porphyrin molecules can result in the formation of interfacial dipole layer between active layer and cathode. The interfacial dipole layer can obviously improve the open-circuit voltage (Voc) and charge extraction, and sequentially lead to the increase of PCE.
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Effect of electron-withdrawing units on triphenylamine-based small molecules for solution-processed organic solar cells

WANG YiFan,BAI HuiTao,CHENG Pei,ZHANG MingYu, ZHAN XiaoWei
Accept: 2014-09-29
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Organic small molecules (TPA-BT3T, TPA-PT3T, and TPA-DFBT3T) using triphenylamine as a donor unit, terthiophene as a bridge, and benzo-2,1,3-thiadiazole (BT), [1,2,5]thiadiazolo[3,4-c]pyridine (PT) or 5,6-difluorobenzo[c][1,2,5]thiadiazole (DFBT) as an acceptor unit were designed and synthesized through Suzuki coupling reactions. These molecules exhibited good thermal stability with decomposition temperatures over 380 oC and broad absorption from 300 to 700 nm. Photovoltaic devices were fabricated with these small molecules as donors and PC71BM as an acceptor. The TPA-BT3T based devices exhibited a power conversion efficiency of 2.89%, higher than those of the TPA-PT3T- and TPA-DFBT3T-based devices (1.34% and 1.54% respectively). The effects of electron-withdrawing units on absorption, energy level, charge transport, morphology, and photovoltaic properties also were investigated.

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Constructing vertical phase separation of polymer blends via mixed solvents to enhance their photovoltaic performance

YANG QingQing, WANG JianTai, ZHANG XiaoQin, ZHANG Jun, FU YingYing, XIE ZhiYuan
Accept: 2014-07-29
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A polymer blend comprising poly(3-hexylthiophene) (P3HT) donor and poly[2,7-(9,9'-octyl-fluorene)-alt-5,5-(4',7'-di-2-thienyl-5',6'-bis(hexyloxy)-2',1',3'-benzothiadiazole)] (PFDTBT-OC6) acceptor is used as the active layer to fabricate all-polymer solar cells. The blend morphology variance processed with pure and mixed solvents, and the related photovoltaic performance, are investigated in detail. It is found that, due to its low surface energy, a thin P3HT enrichment layer on the top surface of the active layer greatly increases bimolecular recombination and results in S-kinks of the illuminated current density-voltage curves. With the incorporation of p-xylene (a marginal solvent of P3HT) in the blend solution, the P3HT enrichment atop the active layer surface is effectively decreased because the high boiling-point p-xylene suppresses the diffusion of P3HT chains toward the top surface during the film-drying process. The bimolecular recombination was thus improved and the S-kinks of the photovoltaic curves were completely removed. The overall power conversion efficiencies of the devices are strongly boosted (from 0.88% to 1.41%) when chlorobenzene:p-xylene mixed solvent is used to replace pure chlorobenzene.
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A New Class of Ion–ion Interaction:Z-bond

DONG Kun, ZHANG Suojiang & WANG Qian
Accept: 2014-05-30
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The hydrogen-bond interactions in ionic liquids have been described by the conventional and simple A-H…B hydrogen bond model. Coupling the strong electrostatic force, however, hydrogen bond between the cation and anion shows particular features in the geometric, energetic, electronic, and dynamic aspects, which is inherently different from that of the conventional hydrogen bond. A general model could be expressed as +[A-H…B]-, in which A and B represent heavy atoms and “+ and –” represent the charges of the cation containing A and anion containing B atoms, respectively. Because the structure shows a “zig-zag” motif, this coupling interaction is defined here as the Z-bond. The new model could be generally used to describe the interactions in ionic liquids, as well as bio-systems involved in ions, ionic reaction, and ionic materials.
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Carbon-free Cu2ZnSn(S,Se)4 film prepared via a non-hydrazine route

ZOU YuGang, LIU Jie, ZHANG Xing, JIANG Yan, HU JinSong, WAN LiJun
Accept: 2014-05-26
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The kesterite Cu2ZnSn(S,Se)4 (CZTSSe) is an ideal candidate for light harvesting materials in earth-abundant low-cost thin-film solar cells (TFSC). Although the solution-based processing is a most promising approach to achieve low-cost solar cells with high power conversion efficiency, the issues of poor crystallinity and carbon residue in CZTSSe thin films are still challenging. Herein, a non-hydrazine solution-based method was reported to fabricate highly crystallized and carbon-free kesterite CZTSSe thin films. Interestingly, it was found that the synthetic atmosphere of metal organic precursors have a dramatic impact on the morphology and crystallinity of CZTSSe films. By optimizing the processing parameters, we are able to obtain a kesterite CZTSSe film composed of compact large crystal grains with trace carbon residues. Also, a
viable reactive ion etching (RIE) processing with optimized etching conditions was then developed to successfully eliminate trace carbon residues on the surface of the CZTSSe film.

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The Fourier space restricted Hartree-Fock method for the electronic structure calculation of linear poly(tetrafluoroethylene)

FRIPIAT Joseph G. & HARRIS Frank E.
Accept: 2014-03-20
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Building on the pioneering work of J.-M. Andre and working in the laboratory he founded, the authors have developed a code called ft-1d to make Hartree-Fock electronic structure computations for stereoregular polymers using Ewald-type convergence acceleration methods. That code also takes full advantage of all line-group symmetries to calculate only the minimal set of two-electron integrals and to optimize the computation of the Fock matrix. The present communication reports a benchmark study of the ft-1d code using polytetrauoroethylene (PTFE) as a test case. Our results not only con rm the algorithmic correctness of the code through agreement with other studies where they are applicable, but also show that the use of convergence acceleration enables accurate results to be obtained in situations where other widely-used codes (e.g., plh and crystal) fail. It is also found that full attention to the line-group symmetry of the PTFE polymer leads to an increase of between one and two orders of magnitude in the speed of computation. The new code can therefore be viewed as extending the range of electronic-structure computations for stereoregular polymers beyond the present scope of the successful and valuable code crystal.

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Stable ZnO/ionic liquid hybrid materials: novel dual-responsive superhydrophobic layers to light and anions

LI HongLiang, XIN BingWei, FENG Lei, HAO JingCheng
Accept: 2014-02-13
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Novel dual-responsive superhydrophobic hybrid materials, ZnO/SAMs (self-assembled monolayers) of ionic liquids (ILs) with different counter-anions (I−, BF4−, PF6− and Tf2N−), were synthesized and characterized. ZnO nanoparticles were first deposited on glass surfaces to produce roughness. Next, SAMs of fluorinated-alkyl-3-(3-triethoxysilylpropyl)-4,5-dihydro-imidazoliumiodide (abb. [C8Ftespim]I) were grafted onto these surfaces via -Si-O- covalent bonds using self-assembly technique. The I− ion could be subsequently exchanged with BF4−, PF6− or Tf2N− through a simple aqueous anion-exchange reaction. The ZnO/ILs hybrid layers were characterized by atomic-force microscope (AFM), scanning-electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Their wettability was estimated through the measurements of static and dynamic contact angles (CAs). Compared to corresponding films of ZnO/[C8Ftespim]I with CAs 140.7 ± 2.0o, films of ZnO/[C8Ftespim]PF6 and ZnO/[C8Ftespim]Tf2N showed CAs with 154.0 ± 2.0o and 152.0 ± 2.0o, respectively, that remained for a long time. This result suggests that anion-exchange can afford superhydrophobic materials. In addition, the wettability of ZnO/[C8Ftespim]X hybrid layers can be reversibly switched by altering ultraviolet (UV) irradiation and dark storage, which shows a photo-induced reversible switch of wettability. The synergistic action of ZnO nanoparticles and SAMs of ILs produced light-anion dual-responsive superhydrophobic materials with ideal stability.

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Recent advances in plasmonic organic photovoltaics

YANG Xi, LIU WenQing, & CHEN HongZheng
Accept: 2014-02-13
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Light trapping based on the localized surface-plasmon resonance (LSPR) effect of metallic nanostructures is a promising strategy to improve the device performance of organic solar cells (OSCs). We review recent advances in plasmonic-enhanced OPVs with solution-processed metallic nanoparticles (NPs).The different types of metallic NPs (sizes, shapes, and hybrids), incorporation positions, and NPs with tunable resonance wavelengths toward broadband enhancement are systematically summarized to give a guideline for the realization of highly efficient plasmonic photovoltaics.
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Two-dimensional photovoltaic copolymers with spatial D-A-D structures: Synthesis, characterization and hetero-atom effect

LI Ying, Xu Xiaopeng, LI Zuojia, YU Ting, & PENG Qiang
Accept: 2014-02-13
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A series of two-dimensional (2D) conjugated copolymers with spatial D-A-D structures (PTNBTB, PTCBTB, and PTSBTB) consisting of hetero-atom-bridged dithiophene and phenylvinyl-substituted benzothiadiazole blocks in the main chain have been designed, synthesized, and characterized. The structure–property relationships of the resulting copolymers were systematically investigated. The effects of the bridging atoms (N, C, and Si) on their thermal, optical, electrochemical and charge-transporting properties were also studied. PTNBTB exhibits a smaller band gap with red-shifted absorption, whereas PTSBTB possesses deeper HOMO level and higher hole mobility than PTCBTB or PTSBTB. Bulk heterojunction (BHJ) solar cells were fabricated and characterized with the conventional configuration of ITO/PEDOT:PSS/copolymer:PC71BM (1:1)/Ca/Al. As expected, PTSBTB devices showed the highest PCE, up to 4.01%, which was due to the lower HOMO level, higher carrier mobility, and stronger optical response as well as the finer nanoscale phase separation of the pristine polymer and/or the corresponding blending active layer with PC71BM. The primary results offer useful insights in designing 2D copolymers with spatial D-A-D backbone and different hetero-atom bridged donor units to finely tune the absorptions, electronic energy levels, carrier mobilities and the photovoltaic properties.

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