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1.
Through first‐principles calculations, it is found that two lattice‐matched halide double‐perovskites, Cs2NaBiBr6 and Cs2AgBiBr6, have a type‐I band alignment and can form highly miscible alloys in which the disordering makes the bandgaps become direct and activates the direct transition from the valence to conduction band edge, leading to a strong optical absorption and high radiative recombination rate. The bandgaps of the alloys are tunable in a wide range of 1.93–3.24 eV, while the lattice constants remain unchanged. This advantage inspires the design of a coherent crystalline matrix based on Cs2(Na,Ag)BiBr6 alloys, in which the Ag‐rich and narrower‐bandgap regions are embedded in the Na‐rich and wide‐bandgap region with lattice‐matched and coherent interfaces. The type‐I band alignment drives the photogenerated excitons into the narrower‐bandgap Ag‐rich regions, so the regions become light‐emitting centers with a high photoluminescence quantum yield (PLQY). The bandgaps of the Ag‐rich regions are tunable, so the color of emitted light can be adjusted, making a broadband emission possible. Such kind of coherent crystalline matrix with high‐PLQY and broadband emission can also be fabricated based on the alloys of other lattice‐matched halide double‐perovskites, demonstrating the flexibility of band structure engineering in the coherent heterostructures of various halide double‐perovskites. 相似文献
2.
Brendan O'Connor R. Joseph Kline Brad R. Conrad Lee J. Richter David Gundlach Michael F. Toney Dean M. DeLongchamp 《Advanced functional materials》2011,21(19):3697-3705
A novel method of strain‐aligning polymer films is introduced and applied to regioregular poly(3‐hexylthiophene) (P3HT), showing several important features of charge transport. The polymer backbone is shown to align in the direction of applied strain resulting in a large charge‐mobility anisotropy, where the in‐plane mobility increases in the applied strain direction and decreases in the perpendicular direction. In the aligned film, the hole mobility is successfully represented by a two‐dimensional tensor, suggesting that charge transport parallel to the polymer backbone within a P3HT crystal is strongly favored over the other crystallographic directions. Hole mobility parallel to the backbone is shown to be high for a mixture of plane‐on and edge‐on packing configurations, as the strain alignment is found to induce a significant face‐on orientation of the originally highly edge‐on oriented crystalline regions of the film. This alignment approach can achieve an optical dichroic ratio of 4.8 and a charge‐mobility anisotropy of 9, providing a simple and effective method to investigate charge‐transport mechanisms in polymer semiconductors. 相似文献
3.
J. Piris M.G. Debije N. Stutzmann B.W. Laursen W. Pisula M.D. Watson T. Bjrnholm K. Müllen J.M. Warman 《Advanced functional materials》2004,14(11):1053-1061
The anisotropy in the optical absorption and photoconductivity of thin layers of mesomorphic derivatives of hexa‐peri‐hexabenzocoronene (HBC) have been investigated for aligned films prepared via three different methods: deposition on friction‐deposited polytetrafluoroethylene (PTFE), zone‐casting (ZC), and Langmuir–Blodgett (LB) multilayer dipping. The ratio of the optical density for light polarized perpendicular to the alignment direction, OD+, to that for light polarized parallel, OD=, varies from close to 1.0 up to 12.5 depending on whether the HBC cores are tilted at close to 45° or 90° with respect to the axis of the self‐assembled columnar stacks. For all aligned films the photoconductivity, determined using the electrode‐less flash‐photolysis time‐resolved microwave conductivity technique (FP‐TRMC), was found to be favored in the direction of columnar alignment by up to a factor of 30 for a PTFE‐aligned film. The effect of varying the temperature of the films over a range encompassing the temperature at which the transition from the crystalline solid to the columnar mesophase occurs in the bulk materials has been investigated. High‐temperature annealing increases the optical and conductivity anisotropy for the LB film significantly, but has little effect for the PTFE and the ZC films. The relative efficacy of the different alignment procedures is discussed. 相似文献
4.
The Effect of Polymer Chain Alignment and Relaxation on Force‐Induced Chemical Reactions in an Elastomer
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Brett A. Beiermann Sharlotte L. B. Kramer Preston A. May Jeffrey S. Moore Scott R. White Nancy R. Sottos 《Advanced functional materials》2014,24(11):1529-1537
Simultaneous measurements of mechanical response, optical birefringence, and fluorescence signal are acquired in situ during tensile testing of a mechanophore‐linked elastomeric polymer. Mechanical stress, deformation, and polymer chain alignment are correlated with force‐induced chemical reaction of the mechanophore. The mechanochemically responsive polymer under investigation is spiropyran‐ (SP‐) linked poly(methyl acrylate) (PMA). Force‐driven conversion (activation) of SP to its merocyanine (MC) form is indicated by the emergence of a fluorescence signal with 532 nm light incident on the sample. Increasing rate of tensile deformation leads to an increase in both stress and SP‐to‐MC conversion, indicating a positive correlation between macroscopic stress and activation. Simultaneously collected birefringence measurements reveal that rapid mechanophore activation occurs when maximum polymer chain alignment is reached. It is found that SP‐to‐MC conversion in PMA requires both a sufficient level of stress and adequate orientation of the polymer chains in the direction of applied force. 相似文献
5.
D. Sainova A. Zen H.‐G. Nothofer U. Asawapirom U. Scherf R. Hagen T. Bieringer S. Kostromine D. Neher 《Advanced functional materials》2002,12(1):49-57
Liquid‐crystalline (LC) polyfluorenes have been successfully aligned on photoaddressable polymers (PAPs). This is the first example of the alignment of a LC main chain polymer on a photoaligned layer. The degree of molecular alignment in the fluorescent polyfluorene layer on top of an ultra‐thin PAP layer is shown to depend strongly on the chemical nature of the PAP. Good alignment with dichroic ratios of more than 10 was only achieved with PAPs containing liquid‐crystalline side chains. Patterning with laterally structured alignment was realized in several ways, utilizing reorientation with orthogonally polarized light. Thin PAP layers have further been utilized as hole‐conducting alignment layers in polymer light‐emitting diodes (LEDs) with polarized emission. In order to facilitate hole transport through the alignment layer, different concentrations of a hole‐transporting molecule (HTM) have been mixed into the PAP layer. These hole‐conducting alignment layers retained their aligning abilities even at HTM concentrations of 20 wt.‐%. LEDs with photometric polarization ratios in emission of up to 14 at a brightness of up to 200 cd/m2 and an efficiency of 0.3 cd/A could be realized. 相似文献
6.
V. Vaenkatesan R.T. Wegh J.‐P. Teunissen J. Lub C.W.M. Bastiaansen D.J. Broer 《Advanced functional materials》2005,15(1):138-142
For most applications of displays based on organic light‐emitting diodes (LEDs), it is desirable to have good daylight contrast in combination with a high intensity of emitted light. The conventional approaches to enhance the daylight contrast, using a black cathode or circular polarizers, result in a significant loss of light emitted by the LED. A rather novel approach to enhance daylight contrast while keeping loss of emitted light to a minimum is the introduction of a chiral‐nematic film in the device. This approach leads to an increase in light efficiency by a factor of 1.8 (with respect to circular polarizers) with some loss in daylight contrast values within the reflection band of the chiral‐nematic film. Outside the reflection band, however, the contrast approaches infinity. 相似文献
7.
Kirill Bulgarevich Kenji Sakamoto Takeo Minari Takeshi Yasuda Kazushi Miki Masayuki Takeuchi 《Advanced functional materials》2019,29(45)
In this study, polymer‐based organic field‐effect transistors (OFETs) that exhibit alignment‐induced mobility enhancement, very small device‐to‐device variation, and high operational stability are successfully fabricated by a simple coating method of semiconductor solutions on highly hydrophobic nanogrooved surfaces. The highly hydrophobic nanogrooved surfaces (water contact angle >110°) are effective at inducing unidirectional alignment of polymer backbone structures with edge‐on orientation and are advantageous for realizing high operational stability because of their water‐repellent nature. The dewetting of the semiconductor solution is a critical problem in the thin film formation on highly hydrophobic surfaces. Dewetting during spin coating is suppressed by surrounding the hydrophobic regions with hydrophilic ones under appropriate designs. For the OFET array with an aligned terrace‐phase active layer of poly(2,5‐bis(3‐hexadecylthiophene‐2‐yl)thieno[3,2‐b]thiophene), the hole mobility in the saturation regime of 30 OFETs with channel current direction parallel to the nanogrooves is 0.513 ± 0.018 cm2 V?1 s?1, which is approximately double that of the OFETs without nanogrooves, and the intrinsic operational stability is comparable to the operational stability of amorphous‐silicon field‐effect transistors. In other words, alignment‐induced mobility enhancement and high operational stability are successfully achieved with very small device‐to‐device variation. This coating method should be a promising means of fabricating high‐performance OFETs. 相似文献
8.
H. Monobe K. Kiyohara N. Terasawa M. Heya K. Awazu Y. Shimizu 《Advanced functional materials》2003,13(12):919-924
The infrared photoinduced alignment change of liquid‐crystal domains was investigated for a hexagonal columnar mesophase of a liquid‐crystalline triphenylene derivative. A uniform and anisotropic alignment change of domains was observed when a polarized infrared (IR) light corresponding to the wavelength of the aromatic C–C stretching absorption band of the triphenylene core was used to irradiate the sample. The relationship between the aligned azimuthal angle of the columnar axis and the polarization of the IR incident irradiation was investigated. IR absorption dichroism is induced as a result of the reorientation of triphenylene core. Texture observation and polarizing microscope FTIR spectra show that a change of the molecular alignment occurred and that the direction of columns depends on the polarization angle of the IR light used for irradiation. The mechanism of the alignment change in a columnar liquid crystal film by IR irradiation is also discussed. The technique could provide a novel technology to control the columnar alignment of highly viscous liquid crystals. 相似文献
9.
Gilberto Siqueira Dimitri Kokkinis Rafael Libanori Michael K. Hausmann Amelia Sydney Gladman Antonia Neels Philippe Tingaut Tanja Zimmermann Jennifer A. Lewis André R. Studart 《Advanced functional materials》2017,27(12)
3D printing of renewable building blocks like cellulose nanocrystals offers an attractive pathway for fabricating sustainable structures. Here, viscoelastic inks composed of anisotropic cellulose nanocrystals (CNC) that enable patterning of 3D objects by direct ink writing are designed and formulated. These concentrated inks are composed of CNC particles suspended in either water or a photopolymerizable monomer solution. The shear‐induced alignment of these anisotropic building blocks during printing is quantified by atomic force microscopy, polarized light microscopy, and 2D wide‐angle X‐ray scattering measurements. Akin to the microreinforcing effect in plant cell walls, the alignment of CNC particles during direct writing yields textured composites with enhanced stiffness along the printing direction. The observations serve as an important step forward toward the development of sustainable materials for 3D printing of cellular architectures with tailored mechanical properties. 相似文献
10.
Energy‐Level Alignment at the Organic/Electrode Interface in Organic Optoelectronic Devices
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Zhanhao Hu Zhiming Zhong Yawen Chen Chen Sun Fei Huang Junbiao Peng Jian Wang Yong Cao 《Advanced functional materials》2016,26(1):129-136
It is commonly believed that the work‐function reduction effect of the cathode interfacial material in organic electronic devices leads to better energy‐level alignment at the organic/electrode interface, which enhances the device performance. However, there is no agreement on the exact dipole direction in the literature. In this study, a peel‐off method to reveal the buried organic/metal interface to examine the energy‐level alignment is developed. By splitting the device at different interfaces, it is discovered that oppositely oriented dipoles are formed at different surfaces of the interfacial layer. Moreover, the function of the electrode interface differs in different device types. In organic light‐emitting diodes, the vacuum‐level alignment generally occurs at the organic/cathode interface, while in organic photovoltaic devices, the Fermi‐level pinning commonly happens. Both are determined by the integer charge‐transfer levels of the organic materials and the work‐function of the electrode. As a result, the performance enhancement by the cathode interfacial material in organic photovoltaic devices cannot be solely explained by the energy‐level alignment. The clarification of the energy‐level alignment not only helps understand the device operation but also sets up a guideline to design the devices with better performance. 相似文献
11.
Thomas S. Parel Lefteris Danos Liping Fang Tomas Markvart 《Progress in Photovoltaics: Research and Applications》2015,23(10):1357-1366
Fluorescent solar concentrators (FSC) can concentrate light onto solar cells by trapping fluorescence through total internal reflection. In an ideal FSC, the major obstacle to efficient photon transport is the re‐absorption of the fluorescence emitted. In order to decompose the contribution of different photon flux streams within a FSC, the angular dependent re‐absorption probability is introduced and modeled in this paper. This is used to analyze the performance of different FSC configurations and is also compared with experimental results. To illustrate the application of the modeling, the collection efficiency of ideal devices has also been calculated from the re‐absorption probability and is shown to be useful for estimating non‐ideal losses such as those due to scattering or reflection from mirrors. The results also indicate that among the FSCs studied, the performance of those surrounded by four edge solar cells is close to ideal. The rapid optimization of FSCs has also been presented as another practical application of the models presented in this paper. © 2014 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons, Ltd. 相似文献
12.
Remote Biosensing with Polychromatic Optical Waveguide Using Blue Light‐Emitting Organic Nanowires Hybridized with Quantum Dots
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Eun Hei Cho Bong‐Gi Kim Sumin Jun Jubok Lee Dong Hyuk Park Kwang‐Sup Lee Jeongyong Kim Jinsang Kim Jinsoo Joo 《Advanced functional materials》2014,24(24):3684-3691
Nanometer‐scale optical waveguides are attractive due to their potential applicability in photonic integration, optoelectronic communication, and optical sensors. Nanoscale white light‐emitting and/or polychromatic optical waveguides are desired for miniature white‐light generators in microphotonic circuits. Here, polychromatic (i.e., blue, green, and red) optical waveguiding characteristics are presented using a novel hybrid composite of highly crystalline blue light‐emitting organic nanowires (NWs) combined with blue, green, and red CdSe/ZnS quantum dots (QDs). Near white‐color waveguiding is achieved for organic NWs hybridized with green and red QDs. Light, emitted from QDs, can be transferred to the organic NW and then optically waveguided through highly packed π‐conjugated organic molecules in the NW with different decay characteristics. Remote biosensing using dye‐attached biomaterials is presented by adapting the transportation of QD‐emitted light through the organic NW. 相似文献
13.
Donghyung Kim Seyoon Jeong Jin Soo Choi Gwanggil Jeon Seungjong Kim Jechang Jeong 《ETRI Journal》2008,30(4):506-515
The H.264/AVC standard has adopted new coding tools such as intra‐prediction, variable block size, motion estimation with quarter‐pixel‐accuracy, loop filter, and so on. The adoption of these tools enables an H.264/AVC‐coded bitstream to have more information than was possible with previous standards. In this paper, we propose an effective spatial error concealment method with low complexity in H.264/AVC intra‐frame. From information included in an H.264/AVC‐coded bitstream, we use prediction modes of intra‐blocks to recover a damaged block. This is because the prediction direction in each prediction mode is highly correlated to the edge direction. We first estimate the edge direction of a damaged block using the prediction modes of the intra‐blocks adjacent to a damaged block and classify the area inside the damaged block into edge and flat areas. Our method then recovers pixel values in the edge area using edge‐directed interpolation, and recovers pixel values in the flat area using weighted interpolation. Simulation results show that the proposed method yields better video quality than conventional approaches. 相似文献
14.
Simultaneous Edge‐on to Face‐on Reorientation and 1D Alignment of Small π‐Conjugated Molecules Using Room‐Temperature Mechanical Rubbing
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Jean‐Charles Ribierre Toshihiko Tanaka Li Zhao Yuki Yokota Shinya Matsumoto Daisuke Hashizume Kazuto Takaishi Tsuyoshi Muto Benoît Heinrich Stéphane Méry Fabrice Mathevet Toshinori Matsushima Masanobu Uchiyama Chihaya Adachi Tetsuya Aoyama 《Advanced functional materials》2018,28(19)
In this study, room‐temperature mechanical rubbing is used to control the 3D orientation of small π‐conjugated molecular systems in solution‐processed polycrystalline thin films without using any alignment substrate. High absorption dichroic ratio and significant anisotropy in charge carrier mobilities (up to 130) measured in transistor configuration are obtained in rubbed organic films based on the ambipolar quinoidal quaterthiophene (QQT(CN)4). Moreover, a solvent vapor annealing treatment of the rubbed film is found to improve the optical and charge transport anisotropy due to an increased crystallinity. X‐ray diffraction and atomic force microscopy measurements demonstrate that rubbing does not only lead to an excellent 1D orientation of the QQT(CN)4 molecules over large areas but also modifies the orientation of the crystals, moving molecules from an edge‐on to a face‐on configuration. The reasons why a mechanical alignment technique can be used at room temperature for such a polycrystalline film are rationalized, by the plastic characteristics of the QQT(CN)4 layer and the role of the flexible alkyl side chains in the molecular packing. This nearly complete conversion from edge‐on to face‐on orientation by mechanical treatment in polycrystalline small‐molecule‐based thin films opens perspectives in terms of fundamental research and practical applications in organic optoelectronics. 相似文献
15.
Simultaneous Tenfold Brightness Enhancement and Emitted‐Light Spectral Tunability in Transparent Ambipolar Organic Light‐Emitting Transistor by Integration of High‐k Photonic Crystal
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Marco Natali Santiago D. Quiroga Luca Passoni Luigino Criante Emilia Benvenuti Gabriele Bolognini Laura Favaretto Manuela Melucci Michele Muccini Francesco Scotognella Fabio Di Fonzo Stefano Toffanin 《Advanced functional materials》2017,27(21)
In organic light‐emitting transistors, the structural properties such as the in‐plane geometry and the lateral charge injection are the key elements that enable the monolithic integration of multiple electronic, optoelectronic, and photonic functions within the same device. Here, the realization of highly integrated multifunctional optoelectronic organic device is reported by introducing a high‐capacitance photonic crystal as a gate dielectric into a transparent single‐layer ambipolar organic light‐emitting transistor (OLET). By engineering the photonic crystal multistack and bandgap, it is showed that the integration of the photonic structure has a twofold effect on the optoelectronic performance of the device, i.e., i) to modulate the spectral profile and outcoupling of the emitted light and ii) to enhance the transistor source–drain current by a 25‐fold factor. Consequently, the photonic‐crystal‐integrated OLET shows an order of magnitude higher emitted power and brightness with respect to the corresponding polymer‐dielectric device, while presenting as‐designed electroluminescence spectral and spatial distribution. The results validate the efficacy of the proposed approach that is expected to unravel the technological potential for the realization of highly integrated optoelectronic smart systems based on organic light‐emitting transistors. 相似文献
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17.
Hybrid Interface States and Spin Polarization at Ferromagnetic Metal–Organic Heterojunctions: Interface Engineering for Efficient Spin Injection in Organic Spintronics
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Shengwei Shi Zhengyi Sun Amilcar Bedoya‐Pinto Patrizio Graziosi Xin Li Xianjie Liu Luis Hueso Valentin A. Dediu Yi Luo Mats Fahlman 《Advanced functional materials》2014,24(30):4812-4821
Ferromagnetic metal–organic semiconductor (FM‐OSC) hybrid interfaces have been shown to play an important role for spin injection in organic spintronics. Here, 11,11,12,12‐tetracyanonaptho‐2,6‐quinodimethane (TNAP) is introduced as an interfacial layer in Co‐OSCs heterojunctions with an aim to tune the spin injection. The Co/TNAP interface is investigated by use of X‐ray and ultraviolet photoelectron spectroscopy (XPS/UPS), near edge X‐ray absorption fine structure (NEXAFS) and X‐ray magnetic circular dichroism (XMCD). Hybrid interface states (HIS) are observed at Co/TNAP interfaces, resulting from chemical interactions between Co and TNAP. The energy level alignment at the Co/TNAP/OSCs interface is also obtained, and a reduction of the hole injection barrier is demonstrated. XMCD results confirm sizeable spin polarization at the Co/TNAP hybrid interface. 相似文献
18.
Wei Chen Dong‐Chen Qi Han Huang Xingyu Gao Andrew T. S. Wee 《Advanced functional materials》2011,21(3):410-424
Organic–organic heterojunctions (OOHs) are critical features in organic light‐emitting diodes, ambipolar organic field‐effect transistors and organic solar cells, which are fundamental building blocks in low‐cost, large‐scale, and flexible electronics. Due to the highly anisotropic nature of π‐conjugated molecules, the molecular orientation of organic thin films can significantly affect the device performance, such as light absorption and charge‐carrier transport, as well as the energy level alignment at OOH interfaces. This Feature Article highlights recent progress in the understanding of interface energetics at small molecule OOH interfaces, focusing on the characterization and fabrication of OOH with well‐defined molecular orientations using a combination of in situ low‐temperature scanning tunneling microscopy, synchrotron‐based high‐resolution ultraviolet photoelectron spectroscopy and near‐edge X‐ray absorption fine structure measurements. The orientation dependent energy level alignments at the OOH interfaces will be discussed in detail. 相似文献
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20.
Luana Persano Sandra Molle Salvatore Girardo Antonio A. R. Neves Andrea Camposeo Ripalta Stabile Roberto Cingolani Dario Pisignano 《Advanced functional materials》2008,18(18):2692-2698
In this work we demonstrate the nanopatterning of nanocomposites made by luminescent zinc oxide nanoparticles and light‐emitting conjugated polymers by means of soft molding lithography. Vertical nanofluidics is exploited to overcome the polymer transport difficulties intrinsic in materials incorporating nanocrystals, and the rheology, fluorescence, absolute quantum yield, and emission directionality of the nanostructured composites are investigated. We study the effect of patterned gratings on the directionality of light emitted from the nanocomposites, finding evidence of the enhancement of forward emitted light, due to the printed wavelength‐scale periodicity. These results open new possibilities for the realization of nanopatterned devices based on hybrid organic‐inorganic systems. 相似文献