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Showing papers in "Advanced Materials in 2009"



Journal ArticleDOI
TL;DR: In this paper, the authors summarize both the basic physics and unresolved aspects of BiFeO3 and device applications, which center on spintronics and memory devices that can be addressed both electrically and magnetically.
Abstract: BiFeO3 is perhaps the only material that is both magnetic and a strong ferroelectric at room temperature. As a result, it has had an impact on the field of multiferroics that is comparable to that of yttrium barium copper oxide (YBCO) on superconductors, with hundreds of publications devoted to it in the past few years. In this Review, we try to summarize both the basic physics and unresolved aspects of BiFeO3 (which are still being discovered with several new phase transitions reported in the past few months) and device applications, which center on spintronics and memory devices that can be addressed both electrically and magnetically.

3,526 citations


Journal ArticleDOI
TL;DR: An outlook is presented on what will be required to drive this young photovoltaic technology towards the next major milestone, a 10% power conversion efficiency, considered by many to represent the efficiency at which OPV can be adopted in wide-spread applications.
Abstract: Solution-processed bulk-heterojunction solar cells have gained serious attention during the last few years and are becoming established as one of the future photovoltaic technologies for low-cost power production. This article reviews the highlights of the last few years, and summarizes today's state-of-the-art performance. An outlook is given on relevant future materials and technologies that have the potential to guide this young photovoltaic technology towards the magic 10% regime. A cost model supplements the technical discussions, with practical aspects any photovoltaic technology needs to fulfil, and answers to the question as to whether low module costs can compensate lower lifetimes and performances.

3,084 citations


Journal ArticleDOI
TL;DR: The properties of hydrogels that are important for tissue engineering applications and the inherent material design constraints and challenges are discussed.
Abstract: Hydrogels, due to their unique biocompatibility, flexible methods of synthesis, range of constituents, and desirable physical characteristics, have been the material of choice for many applications in regenerative medicine. They can serve as scaffolds that provide structural integrity to tissue constructs, control drug and protein delivery to tissues and cultures, and serve as adhesives or barriers between tissue and material surfaces. In this work, the properties of hydrogels that are important for tissue engineering applications and the inherent material design constraints and challenges are discussed. Recent research involving several different hydrogels polymerized from a variety of synthetic and natural monomers using typical and novel synthetic methods are highlighted. Finally, special attention is given to the microfabrication techniques that are currently resulting in important advances in the field.

2,339 citations


Journal ArticleDOI
TL;DR: Of all the possible nanoparticle shapes, gold nanorods are especially intriguing as they offer strong plasmonic fields while exhibiting excellent tunability and biocompatibility, according to a review of their radiative and nonradiative properties.
Abstract: Noble metal nanoparticles are capable of confining resonant photons in such a manner as to induce coherent surface plasmon oscillation of their conduction band electrons, a phenomenon leading to two important properties. Firstly, the confinement of the photon to the nanoparticle's dimensions leads to a large increase in its electromagnetic field and consequently great enhancement of all the nanoparticle's radiative properties, such as absorption and scattering. Moreover, by confining the photon's wavelength to the nanoparticle's small dimensions, there exists enhanced imaging resolving powers, which extend well below the diffraction limit, a property of considerable importance in potential device applications. Secondly, the strongly absorbed light by the nanoparticles is followed by a rapid dephasing of the coherent electron motion in tandem with an equally rapid energy transfer to the lattice, a process integral to the technologically relevant photothermal properties of plasmonic nanoparticles. Of all the possible nanoparticle shapes, gold nanorods are especially intriguing as they offer strong plasmonic fields while exhibiting excellent tunability and biocompatibility. We begin this review of gold nanorods by summarizing their radiative and nonradiative properties. Their various synthetic methods are then outlined with an emphasis on the seed-mediated chemical growth. In particular, we describe nanorod spontaneous self-assembly, chemically driven assembly, and polymer-based alignment. The final section details current studies aimed at applications in the biological and biomedical fields.

1,713 citations


Journal ArticleDOI
TL;DR: In this article, a review of recent developments in the use of ZnO nanostructures for dye-sensitized solar cell (DSC) applications is presented.
Abstract: This Review focuses on recent developments in the use of ZnO nanostructures for dye-sensitized solar cell (DSC) applications. It is shown that carefully designed and fabricated nanostructured ZnO films are advantageous for use as a DSC photoelectrode as they offer larger surface areas than bulk film material, direct electron pathways, or effective light-scattering centers, and, when combined with TiO2, produce a core–shell structure that reduces the combination rate. The limitations of ZnO-based DSCs are also discussed and several possible methods are proposed so as to expand the knowledge of ZnO to TiO2, motivating further improvement in the power-conversion efficiency of DSCs.

1,627 citations


Journal ArticleDOI
TL;DR: Recent research has been conducted to develop nanoparticle‐based T1 contrast agents to overcome the drawbacks of iron oxide nanoparticles‐based negative T2 contrast agents.
Abstract: Various inorganic nanoparticles have been used as magnetic resonance imaging (MRI) contrast agents due to their unique properties, such as large surface area and efficient contrasting effect. Since the first use of superparamagnetic iron oxide (SPIO) as a liver contrast agent, nanoparticulate MRI contrast agents have attracted a lot of attention. Magnetic iron oxide nanoparticles have been extensively used as MRI contrast agents due to their ability to shorten T2* relaxation times in the liver, spleen, and bone marrow. More recently, uniform ferrite nanoparticles with high crystallinity have been successfully employed as new T2 MRI contrast agents with improved relaxation properties. Iron oxide nanoparticles functionalized with targeting agents have been used for targeted imaging via the site-specific accumulation of nanoparticles at the targets of interest. Recently, extensive research has been conducted to develop nanoparticle-based T1 contrast agents to overcome the drawbacks of iron oxide nanoparticle-based negative T2 contrast agents. In this report, we summarize the recent progress in inorganic nanoparticle-based MRI contrast agents.

1,624 citations


Journal ArticleDOI
TL;DR: In this article, a review of recent progress dedicated to the anode and cathode materials that have the potential to fulfil the crucial factors of cost, safety, lifetime, durability, power density, and energy density is presented.
Abstract: In order to address power and energy demands of mobile electronics and electric cars, Li-ion technology is urgently being optimized by using alternative materials. This article presents a review of our recent progress dedicated to the anode and cathode materials that have the potential to fulfil the crucial factors of cost, safety, lifetime, durability, power density, and energy density. Nanostructured inorganic compounds have been extensively investigated. Size effects revealed in the storage of lithium through micropores (hard carbon spheres), alloys (Si, SnSb), and conversion reactions (Cr(2)O(3), MnO) are studied. The formation of nano/micro core-shell, dispersed composite, and surface pinning structures can improve their cycling performance. Surface coating on LiCoO(2) and LiMn(2)O(4) was found to be an effective way to enhance their thermal and chemical stability and the mechanisms are discussed. Theoretical simulations and experiments on LiFePO(4) reveal that alkali metal ions and nitrogen doping into the LiFePO(4) lattice are possible approaches to increase its electronic conductivity and does not block transport of lithium ion along the 1D channel.

1,596 citations


Journal ArticleDOI
TL;DR: In this paper, Boron and nitrogen-doped graphenes are prepared by the arc discharge between carbon electrodes or by the transformation of nanodiamond under appropriate atmospheres using a combination of experiment and theories based on first principles.
Abstract: Boron- and nitrogen-doped graphenes are are prepared by the arc discharge between carbon electrodes or by the transformation of nanodiamond under appropriate atmospheres. Using a combination of experiment and theories based on first principles, systematic changes in the carrier-concentration and electronic structure of the doped graphenes are demonstrated. Stiffening of the G-band mode and intensification of the defect-related D-band in the Raman spectra are also observed.

1,579 citations


Journal ArticleDOI
TL;DR: A review of recent work on modeling of organic/metal and organic/organic interfaces can be found in this article, where the strength of the interaction at the interface has been used as the main factor.
Abstract: In this Review, we summarize recent work on modeling of organic/metal and organic/organic interfaces. Some of the models discussed have a semiempirical approach, that is, experimentally derived values are used in combination with theory, and others rely completely of calculations. The models are categorized according to the types of interfaces they apply to, and the strength of the interaction at the interface has been used as the main factor. We explain the basics of the models, their use, and give examples on how the models correlate with experimental results. We stress that given the complexity of organic/metal and organic/organic interface formation, it is crucial to know the exact way in which the interface was formed before choosing the model that is applicable, as none of the models presented covers the whole range of interface interaction strengths (weak physisorption to strong chemisorption).

1,436 citations



Journal ArticleDOI
TL;DR: The literature and advances in photocatalysis based on the combination of titania (TiO2) and carbon nanotubes is presented in this paper, and the proposed mechanisms of catalytic enhancement resulting from the pairing of the titania semiconductor with either metallic, semiconducting, or defect-rich carbon nanotsubes (CNT) is discussed.
Abstract: The literature and advances in photocatalysis based on the combination of titania (TiO2) and carbon nanotubes is presented. The semiconductor basis for photocatalysis is introduced for anatase and rutile. Furthermore, the proposed mechanisms of catalytic enhancement resulting from the pairing of the titania semiconductor with either metallic, semiconducting, or defect-rich carbon nanotubes (CNT) is discussed. Differences are apparent for the mixtures and chemically bonded CNT–TiO2 composites. The article then highlights the recent advances in the synthesis techniques for these composites and their photocatalytic reactions with organic, inorganic, and biological agents. Finally, various applications and challenges for these composite materials are reported.

Journal ArticleDOI
TL;DR: A facile two-step aqueous approach to immobilization of biomolecules onto surfaces is reported, which exploits the latent reactivity of the biomimetic polymer thin film towards nucleophiles, is unaffected by water, and allows for discrimination betweenucleophiles on the basis of pKa.
Abstract: Immobilization of biomolecules onto surfaces is important in many of the biological and physical sciences, including cell and molecular biology, analytical chemistry, and in applied and interdisciplinary fields such as medical diagnostics, tissue engineering, and bioprocess engineering.[1-4] Strategies for biomolecule immobilization onto surfaces generally exploit either noncovalent or covalent reactions. Noncovalent methods allow reversible immobilization of biomolecules under specific conditions, and include physical adsorption and affinity immobilization. Some widely adapted examples are (strep)avidin-biotin, nitriloacetic acid (NTA)-histidine, and DNA-DNA interactions.[5-8] In contrast, covalent immobilization of molecules onto surfaces typically relies on conjugation reactions between ‘active’ functional groups, such as N-hydroxysuccinimide (NHS)[9] or maleimide,[10] and companion target moieties, such as amines and sulfhydryls. For reactions involving biomolecules performed in aqueous solvents, susceptibility of NHS, maleimide, and other activating groups to hydrolysis during storage and reaction can lead to low efficiency of surface bioconjugation.[11,12] In this study, we report a facile two-step aqueous approach to immobilization of biomolecules onto surfaces. The approach involves simple dip-coating of a biomimetic polymer thin film onto a substrate, followed by conjugation of biomolecules to the biomimetic polymer film. The method exploits the latent reactivity of the biomimetic polymer thin film towards nucleophiles, is unaffected by water, and allows for discrimination between nucleophiles on the basis of pKa.

Journal ArticleDOI
TL;DR: In this article, a review of polymer morphology is presented with respect to solvent selection and various annealing processes, which facilitates the formation of optimal percolation paths and therefore provides a simple approach to improve photovoltaic performance.
Abstract: Polymer morphology has proven to be extremely important in determining the optoelectronic properties in polymer-based devices. The understanding and manipulation of polymer morphology has been the focus of electronic and optoelectronic polymer-device research. In this article, recent advances in the understanding and controlling of polymer morphology are reviewed with respect to the solvent selection and various annealing processes. We also review the mixed-solvent effects on the dynamics of film evolution in selected polymer-blend systems, which facilitate the formation of optimal percolation paths and therefore provide a simple approach to improve photovoltaic performance. Recently, the occurrence of vertical phase separation has been found in some polymer:fullerene bulk heterojunctions. [1-3] The origin and applications of this inhomogeneous distribution of the polymer donor and fullerene acceptor are addressed. The current status and device physics of the inverted structure solar cells is also reviewed, including the advantage of utilizing the spontaneous vertical phase separation, which provides a promising alternative to the conventional structure for obtaining higher device performance.

Journal ArticleDOI
TL;DR: Wang et al. as discussed by the authors proposed a method for the extraction of Colloid Chemistry Max-Planck Institute of Colloids and Interfaces Research Campus Golm, 14476 Potsdam (Germany).
Abstract: [*] Prof. X. C. Wang, X. F. Chen, Prof. X. Z. Fu Research Institute of Photocatalysis State Key Laboratory Breeding Base of Photocatalysis Fuzhou University, Fuzhou 350002 (PR China) E-mail: xcwang@fzu.edu.cn; xzfu@fzu.edu.cn Prof. X. C. Wang, Dr. A. Thomas, Prof. M. Antonietti Department of Colloid Chemistry Max-Planck Institute of Colloids and Interfaces Research Campus Golm, 14476 Potsdam (Germany)

Journal ArticleDOI
TL;DR: In this paper, the authors present a review of recent advances in assembly techniques for forming ultrathin carbon nanotubes, modeling and experimental work that reveals their collective properties, and engineering aspects of implementation in sensors and in electronic devices and circuits with various levels of complexity.
Abstract: Ultrathin films of single-walled carbon nanotubes (SWNTs) represent an attractive, emerging class of material, with properties that can approach the exceptional electrical, mechanical, and optical characteristics of individual SWNTs, in a format that, unlike isolated tubes, is readily suitable for scalable integration into devices. These features suggest the potential for realistic applications as conducting or semiconducting layers in diverse types of electronic, optoelectronic and sensor systems. This article reviews recent advances in assembly techniques for forming such films, modeling and experimental work that reveals their collective properties, and engineering aspects of implementation in sensors and in electronic devices and circuits with various levels of complexity. A concluding discussion provides some perspectives on possibilities for future work in fundamental and applied aspects.


Journal ArticleDOI
TL;DR: In this article, the progress of lithium storage in different carbon forms starting from intercalation in graphite to the storage in fullerenes, nanotubes, diamond and most recently, graphene is discussed.
Abstract: In this review article we discuss the progress of lithium storage in different carbon forms starting from intercalation in graphite to the lithium storage in fullerenes, nanotubes, diamond and most recently, graphene. The recent advances in lithium storage in various novel morphological variants of carbons prepared by a variety of techniques are also discussed with the most important models in literature that have been set out to explain the excess lithium storage. The major emphasis lies on the real structure.

Journal ArticleDOI
TL;DR: In this paper, the authors used facilities available through the Cornell Center for Materials Research (CCMR) and Cornell Integrated Microscopy Center (CIMC) for their work.
Abstract: This publication was based on work supported by Award No. KUS-C1-018-02, made by King Abdullah University of Science and Technology (KAUST). We are also grateful to the National Science Foundation (DMR 0404278) for partial support. Facilities available through the Cornell Center for Materials Research (CCMR), and Cornell Integrated Microscopy Center (CIMC) were used for this study. Supporting Information is available online from Wiley InterScience or from the author. This article has been amended for print publication.


Journal ArticleDOI
TL;DR: In this paper, the authors review various aspects of fabrication, characterization, device implementation and operation of carbon nanotube-polymer composites to be used in photonic applications.
Abstract: Polymer composites are one of the most attractive near-term means to exploit the unique properties of carbon nanotubes and graphene. This is particularly true for composites aimed at electronics and photonics, where a number of promising applications have already been demonstrated. One such example is nanotube-based saturable absorbers. These can be used as all-optical switches, optical amplifier noise suppressors, or mode-lockers to generate ultrashort laser pulses. Here, we review various aspects of fabrication, characterization, device implementation and operation of nanotube-polymer composites to be used in photonic applications. We also summarize recent results on graphene-based saturable absorbers for ultrafast lasers.

Journal ArticleDOI
TL;DR: Nogi et al. as discussed by the authors proposed an optically transparent paper with low thermal expansion (CTE <8.5 ppm K ) using 15 nm cellulose nanofibers with the same chemical constituents as conventional paper and a production process also similar to conventional paper.
Abstract: M Optically Transparent Nanofiber Paper M U N IC By Masaya Nogi,* Shinichiro Iwamoto, Antonio Norio Nakagaito, and Hiroyuki Yano A T IO N Glass has well-suited low thermal expansion for use in electronic devices, but it is fragile, and the search for a stronger, more flexible optically clear medium has gone on for many years. Plastics have been widely studied; however, most of them have large coefficients of thermal expansion (CTE, approx. 50 ppm K ), and foldable plastics in particular exhibit extremely large CTEs, in excess of 200 ppm K . Further, the functional materials deposited on plastic substrates are prone to be damaged by the temperatures involved in the assembly and mounting processes due to themismatch between CTEs from differentmaterials. This article reports on what might be best described as optically transparent paper. It is a foldable nanofiber material with low thermal expansion (CTE <8.5 ppm K ) prepared using 15 nm cellulose nanofibers with the same chemical constituents as conventional paper and a production process also similar to that of conventional paper. The only difference is in the fiber width and the size of the interstitial cavities (Fig. 1). The foldable, low-CTE, and optically transparent nanofiber paper is the perfect candidate for substrates for continuous roll-to-roll processing in the future production of electronic devices, such as flexible displays, solar cells, e-papers, and a myriad of new flexible circuit technologies, and could replace the costly conventional batch processes based on glass substrates currently used. We project that it will also replace conventional paper as an advanced information medium, which can still be produced using traditional paper-making equipment that is used in production today. Cellulose nanofibers are the main component of plant and wood pulp fibers. These tiny elements with diameters of 15–20 nm are composed of bundles of cellulose microfibrils smaller than 4 nm in width, which, in turn, are composed of long cellulose molecules laterally stabilized by hydrogen bonds forming highly crystalline domains. As such, cellulose nanofibers have a CTE of 0.1 ppm K , which is as low as that of quartz glass, and an estimated strength of 2–3 GPa, rendering it five times stronger than mild steel. The nanofibers also exhibit good heat-transfer properties comparable to glass. Another significant property of the nanofibers is that light scattering can be suppressed. If the cellulose nanofibers are densely packed, and the interstices between the fibers are small enough to avoid


Journal ArticleDOI
TL;DR: A thermodynamic model for receptor-mediated endocytosis of ligand-coated NPs is presented, and an optimal NP radius is identified at which the cellular uptake reaches a maximum of several thousand at physiologically relevant parameters, and it is shown that the cell uptake is regulated by membrane tension, and can be elaborately controlled by particle size.
Abstract: Recent advances in nanotechnology have stimulated novel applications in biomedicine where nanoparticles (NPs) are used to achieve drug delivery and photodynamic therapy. In chemotherapeutic cancer treatment, tumor-specific drug delivery is a topic of considerable research interest for achieving enhanced therapeutic efficacy and for mitigating adverse side effects. Most anticancer agents are incapable of distinguishing between benign and malignant cells, and consequently cause systematic toxicity during cancer treatment. Owing to their small size, ligand-coated NPs can be efficiently directed toward, and subsequently internalized by tumor cells through ligand–receptor recognition and interaction (see Fig. 1), thereby offering an effective approach for specific targeting of tumor cells. For example, branching dendrimers have recently been identified as potential candidates for site-specific drug carriers.[2] NPs have also been exploited in other biomedical applications such as bioimaging[3,4] and biosensing.[5,6] It has been demonstrated that florescent quantum dots are efficient in tumor cell imaging, recognition, and tracking,[3,4] and that gold NPs are capable of detecting small proteins.[5,6] To enable rational design of such NP-based agents, it is essential to understand the underlying mechanisms that govern the transmembrane transport and invagination of NPs in biological cells. In this communication, we present a thermodynamic model for receptor-mediated endocytosis of ligand-coated NPs. We identify an optimal NP radius at which the cellular uptake reaches a maximum of several thousand at physiologically relevant parameters, and we show that the cellular uptake of NPs is regulated by membrane tension, and can be elaborately controlled by particle size. The optimal NP radius for endocytosis is on the order of 25−30 nm, which is in good agreement with prior estimates.[7]

Journal ArticleDOI
TL;DR: The recent development of strong hydrogels suggests that it may be possible to design new families of strong gels that would allow the design of soft biomimetic machines, which have not previously been possible.
Abstract: Hydrogels have applications in surgery and drug delivery, but are never considered alongside polymers and composites as materials for mechanical design. This is because synthetic hydrogels are in general very weak. In contrast, many biological gel composites, such as cartilage, are quite strong, and function as tough, shock-absorbing structural solids. The recent development of strong hydrogels suggests that it may be possible to design new families of strong gels that would allow the design of soft biomimetic machines, which have not previously been possible.

Journal ArticleDOI
TL;DR: A series of recent reports has shown that poly(aryleneethynylene)s (PAEs), poly(phenyl-ene butadiynylene), polyphenylene vinylene, poly(p-phenylene) s, polysilanes, polyanilines, and polytriazines can be produced as microporous networks with apparent Brunauer-Emmett-Teller surface areas of more than 1000m2 g−1 in some cases as discussed by the authors.
Abstract: Conjugated microporous polymers are of great interest because they have potential to combine high surface areas in the dry state with physical properties relevant to organic electronics. A series of recent reports has shown that materials such as poly(aryleneethynylene)s (PAEs), poly(phenyl-ene butadiynylene)s, poly(phenylene vinylene), poly(p-phenylene)s, polysilanes, polyanilines, and polytriazines can be produced as microporous networks with apparent Brunauer–Emmett–Teller surface areas of more than 1000 m2 g−1 in some cases. Micropore size and surface area can be synthetically fine tuned in amorphous PAE polymers and copolymers, something which was previously thought to be the preserve of ordered crystalline materials such as metal organic frameworks. We review in this Research News article recent progress made by our group and others with particular emphasis on the possible future applications of these materials.

Journal ArticleDOI
TL;DR: Chen, Chengmeng, Yang, Quan-Hong; Yang, Yonggang; Lv, Wei; Wen, Yuefang; Wang, Maozhang] Tianjin Univ, Sch Chem Engn & Technol, Key Lab Green Chem Tech, Tianjin 300072, Peoples R China;qhyangcn@tju.edu.cn yangyg@sxicc.ac.cn
Abstract: [Chen, Chengmeng; Yang, Quan-Hong; Yang, Yonggang; Lv, Wei; Wen, Yuefang; Wang, Maozhang] Tianjin Univ, Sch Chem Engn & Technol, Key Lab Green Chem Technol, Minist Educ, Tianjin 300072, Peoples R China. [Chen, Chengmeng] Chinese Acad Sci, Grad Univ, Beijing 100049, Peoples R China. [Hou, Peng-Xiang; Cheng, Hui-Ming] Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 100016, Peoples R China.;Yang, QH (reprint author), Tianjin Univ, Sch Chem Engn & Technol, Key Lab Green Chem Technol, Minist Educ, Tianjin 300072, Peoples R China;qhyangcn@tju.edu.cn yangyg@sxicc.ac.cn

Journal ArticleDOI
TL;DR: In this article, Choi et al. proposed a method to solve the problem of display device and processing at the Samsung Advanced Institute of Technology (SAIT) in Suwon, Korea.
Abstract: [*] Dr. J.-Y. Choi, H.-J. Shin, S.-M. Yoon Display Device and Processing Laboratory Samsung Advanced Institute of Technology PO Box 111, Suwon 440-600 (Republic of Korea) E-mail: jaeyoung88.choi@samsung.com Prof. Y. H. Lee, S. J. Chae, F. Gunes, Dr. K. K. Kim, E. S. Kim, G. H. Han, S. M. Kim, H.-J. Shin BK21 Physics Division Sungkyunkwan Advanced Institute of Nanotechnology Center for Nanotubes and Nanostructured Composites Sungkyunkwan University Suwon 440-746 (Republic of Korea) E-mail: leeyoung@skku.edu M. H. Park, Prof. C. W. Yang Department of Advanced Materials Engineering Sungkyunkwan University Suwon 440-746 (Republic of Korea)

Journal ArticleDOI
TL;DR: This review provides an overview of the latest advances in Ln(3+)-containing siloxane-based hybrids, with emphasis on the different possible synthetic strategies, photoluminescence features, empirical determination.
Abstract: Interest in lanthanide-containing organic-inorganic hybrids has grown considerably during the last decade, with the concomitant fabrication of materials with tunable attributes offering modulated properties. The potential of these materials relies on exploiting the synergy between the intrinsic characteristics of sol-gel derived hosts (highly controlled purity, versatile shaping and patterning, excellent optical quality, easy control of the refractive index, photosensitivity, encapsulation of large amounts of isolated emitting centers protected by the host) and the luminescence features of trivalent lanthanide ions (high luminescence quantum yield, narrow bandwidth, long-lived emission, large Stokes shifts, ligand-dependent luminescence sensitization). Promising applications may be envisaged, such as light-emitting devices, active waveguides in the visible and near-IR spectral regions, active coatings, and bio-medical actuators and sensors, opening up exciting directions in materials science and related technologies with significant implications in the integration, miniaturization, and multifunctionalization of devices. This review provides an overview of the latest advances in Ln(3+)-containing siloxane-based hybrids, with emphasis on the different possible synthetic strategies, photoluminescence features, empirical determination.

Journal ArticleDOI
TL;DR: In this article, the authors used a two-dimensional, periodic array of Ag strips on a silica-coated Si film supported by a silicon substrate to achieve a 43% enhancement in the short circuit current as compared to a cell without metallic structures.
Abstract: Basic design rules are developed for the use of metallic nanostructures to realize broadband absorption enhancements in thin-film solar cells. They are applied to a relevant and physically intuitive model system consisting of a two-dimensional, periodic array of Ag strips on a silica-coated Si film supported by a silica substrate. We illustrate how one can simultaneously take advantage of 1) the high near-fields surrounding the nanostructures close to their surface plasmon resonance frequency and 2) the effective coupling to waveguide modes supported by the thin Si film through an optimization of the array properties. Following this approach, we can attain a 43% enhancement in the short circuit current as compared to a cell without metallic structures. It is suggested that 3-dimensional nanoparticle arrays with even larger boosts in short circuit current can also be generated using the presented framework. Photovoltaic (PV) cells can provide virtually unlimited amounts of energy by effectively converting sunlight into clean electrical power. Silicon has been the material of choice for PV cells due to low cost, earth abundance, non-toxicity, and the availability of a very mature processing technology. The cost of current PV modules still needs to be significantly reduced and efficiency substantially increased to enable large scale implementation. Thin-film, second-generation Si solar cells may provide a viable pathway towards this goal because of their low materials and processing costs. Unfortunately the materials quality and resulting energy conversion efficiencies of such cells are still substantially lower than crystalline, wafer-based cells. This is a direct result of the large mismatch between electronic and photonic length scales in these devices; the absorption depth of light in Si is significantly longer than the electronic (minority carrier) diffusion length in deposited thin-film materials for photon energies close to the band-gap. As a result, charge extraction from optically thick cells is challenging due to carrier recombination in the bulk of the semiconductor. If light absorption could be improved in ultra-thin layers of active material it would lead directly to lower recombination currents, higher open circuit voltages, and higher conversion efficiencies. Conventional, planar anti-reflection (AR) coatings do not provide high transmission efficiencies over the entire solar spectrum and do not enable effective light trapping to increase absorption. Light trapping schemes using diffusely scattering surface textures were first suggested in the 1980s and are by now fairly-well understood. Texturing surfaces of thin film cells is not ideal as it leads to enhanced surface recombination. For this reason, some interesting alternative trapping configurations have been proposed that utilize structuring at length-scales orders of magnitude larger than the cell thickness. More than a decade ago, it was first proposed to use the unique optical properties of metallic (i.e., plasmonic) structures to boost the efficiency of PV cells; those metallic nanostructures exhibit easily accessible collective electron oscillations known as surface plasmons. Surface plasmon excitations enable unparalleled light concentration and trapping. Since these pioneering efforts, plasmonics has also been used to enable new photodetector designs that exploit lateral and in-depth light concentration to increase their signal-to-noise ratio and speed in the visible, near-IR, and mid-IR wavelength ranges. Recently, the use of metallic nanostructures for PV has received renewed attention with the availability of new nanofabrication tools and the growing understanding of their optical properties provided by the burgeoning field of plasmonics. In different cell designs both near-field light concentration close to the individual particle resonance and effective light trapping by nanometallics have been explored. Experimentally, high peak enhancements in the tens of percent range at specific wavelengths and overall efficiency enhancements of 40%, 8.3%, and 8% have been achieved with the use of plasmonic structures for cells employing organics, a-Si, and GaAs, respectively. Separate efforts have focused on increasing the more omni-directional absorption characteristics for solar tracking and operation in diffuse sunlight. These results are very promising, although no detailed comparisons have yet been made to cells employing alternative light trapping technologies. Moreover, there is a clear need for effective optimization strategies that lead to broadband absorption enhancements over the entire solar spectrum. This type of optimization for nanostructured solar cells is now within the realm of possibilities; the recent advances in full-field electromagnetic simulations and computer hardware have resulted in the development of extremely accurate and robust optimization tools that are now commonly used by the PV community. In this paper, we illustrate a straightforward and physically intuitive procedure to optimize the net overall absorption of a thin-film Si solar cell over the entire solar spectrum; this simultaneously takes advantage of 1) the high near-fields surrounding the nanostructures close to their surface plasmon C O M M U N IC A TI O N www.advmat.de