Showing papers in "Nature Photonics in 2012"
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TL;DR: In this article, a review summarizes recent progress in the development of polymer solar cells and provides a synopsis of major achievements in the field over the past few years, while potential future developments and the applications of this technology are also briefly discussed.
Abstract: This Review summarizes recent progress in the development of polymer solar cells. It covers the scientific origins and basic properties of polymer solar cell technology, material requirements and device operation mechanisms, while also providing a synopsis of major achievements in the field over the past few years. Potential future developments and the applications of this technology are also briefly discussed.
3,832 citations
TL;DR: In this article, the authors showed that PFN can be incorporated into polymer light-emitting devices (PLEDs) to enhance electron injection from high-work-function metals such as aluminium (work function w of 4.3 eV) and gold (w ¼ 5.2 eV).
Abstract: typically based on n-type metal oxides, our device is solutionprocessed at room temperature, enabling easy processibility over a large area. Accordingly, the approach is fully amenable to highthroughput roll-to-roll manufacturing techniques, may be used to fabricate vacuum-deposition-free PSCs of large area, and find practical applications in future mass production. Moreover, our discovery overturns a well-accepted belief (the inferior performance of inverted PSCs) and clearly shows that the characteristics of high performance, improved stability and ease of use can be integrated into a single device, as long as the devices are optimized, both optically and electrically, by means of a meticulously designed device structure. We also anticipate that our findings will catalyse the development of new device structures and may move the efficiency of devices towards the goal of 10% for various material systems. Previously, we reported that PFN can be incorporated into polymer light-emitting devices (PLEDs) to enhance electron injection from high-work-function metals such as aluminium (work function w of 4.3 eV) 22,23 and has thus been used to realize high-efficiency, air-stable PLEDs 24 . Furthermore, we also found that efficient electron injection can be obtained even in the most noble metals with extremely high work functions, such as gold (w ¼ 5.2 eV), by lowering the effective work function (for example lowering w in gold by 1.0 eV), which has previously been ascribed to the formation of a strong interface dipole 25 .
3,651 citations
TL;DR: In this paper, the authors demonstrate the ability to multiplex and transfer data between twisted beams of light with different amounts of orbital angular momentum, which provides new opportunities for increasing the data capacity of free-space optical communications links.
Abstract: Researchers demonstrate the ability to multiplex and transfer data between twisted beams of light with different amounts of orbital angular momentum — a development that provides new opportunities for increasing the data capacity of free-space optical communications links.
3,556 citations
TL;DR: In this paper, a vision for a future sustainable hydrogen fuel community based on artificial photosynthesis is outlined and current progress towards artificial photosynthetic devices is reviewed, with particular focus on visible light active nanostructures.
Abstract: Hydrogen from solar-driven water splitting has the potential to provide clean energy. Current progress towards artificial photosynthetic devices is reviewed, with particular focus on visible light active nanostructures. A vision for a future sustainable hydrogen fuel community based on artificial photosynthesis is outlined.
1,703 citations
TL;DR: In this article, the authors compared carbon nanotube, metal nanowire networks, and regular metal grids with the usual transparent conductive oxides for optically transparent electrode applications.
Abstract: Increasing demand for raw materials means that alternatives to indium-tin oxide are desired for optically transparent electrode applications. Carbon nanotube, metal nanowire networks and regular metal grids have been investigated as possible options. In this review, these materials and recently rediscovered graphene are compared with the usual transparent conductive oxides.
1,697 citations
TL;DR: In this paper, the SPring-8 Angstrom Compact Free-Electron Laser (CFEL) was used for sub-angstrom fundamental-wavelength lasing at the Tokyo National Museum.
Abstract: Researchers report sub-angstrom fundamental-wavelength lasing at the SPring-8 Angstrom Compact Free-Electron Laser in Japan. The output has a maximum power of more than 10 GW, a pulse duration of 10−14 s and a lasing wavelength of 0.634 A.
1,467 citations
TL;DR: In this paper, the authors demonstrate that PBDTT-DPP, a semiconducting polymer with a low bandgap of 1.44 eV, allows tandem polymer solar cells to reach power conversion efficiencies of around 8.6%.
Abstract: Researchers demonstrate that PBDTT-DPP, a semiconducting polymer with a low bandgap of 1.44 eV, allows tandem polymer solar cells to reach power conversion efficiencies of around 8.6%.
1,406 citations
TL;DR: In this paper, the concept of dissipative solitons and their application to high-energy mode-locked fiber laser cavities are discussed, and an outlook of the field is also provided.
Abstract: This Review explains the concept of dissipative solitons and their application to high-energy mode-locked fibre laser cavities. Dynamics and effects such as dissipative soliton ‘explosions’ and ‘rain’ are summarized, and an outlook of the field is also provided.
1,322 citations
TL;DR: In this article, the authors used strongly scattering materials to focus, shape and compress waves by controlling the many degrees of freedom in the incident waves in complex media such as white paint and biological tissue.
Abstract: In complex media such as white paint and biological tissue, light encounters nanoscale refractive-index inhomogeneities that cause multiple scattering. Such scattering is usually seen as an impediment to focusing and imaging. However, scientists have recently used strongly scattering materials to focus, shape and compress waves by controlling the many degrees of freedom in the incident waves. This was first demonstrated in the acoustic and microwave domains using time reversal, and is now being performed in the optical realm using spatial light modulators to address the many thousands of spatial degrees of freedom of light. This approach is being used to investigate phenomena such as optical super-resolution and the time reversal of light, thus opening many new avenues for imaging and focusing in turbid media
1,322 citations
TL;DR: In this paper, a high-work-function, low-sheet-resistance graphene anode was used to improve the luminous efficiency of organic light-emitting diodes (OLEDs).
Abstract: Although graphene films have a strong potential to replace indium tin oxide anodes in organic light-emitting diodes (OLEDs), to date, the luminous efficiency of OLEDs with graphene anodes has been limited by a lack of efficient methods to improve the low work function and reduce the sheet resistance of graphene films to the levels required for electrodes1,2,3,4. Here, we fabricate flexible OLEDs by modifying the graphene anode to have a high work function and low sheet resistance, and thus achieve extremely high luminous efficiencies (37.2 lm W–1 in fluorescent OLEDs, 102.7 lm W–1 in phosphorescent OLEDs), which are significantly higher than those of optimized devices with an indium tin oxide anode (24.1 lm W–1 in fluorescent OLEDs, 85.6 lm W–1 in phosphorescent OLEDs). We also fabricate flexible white OLED lighting devices using the graphene anode. These results demonstrate the great potential of graphene anodes for use in a wide variety of high-performance flexible organic optoelectronics. By replacing conventional indium tin oxide (ITO) anodes with high-work-function, low-sheet-resistance graphene anodes, researchers demonstrate flexible fluorescent organic LEDs with extremely high luminous efficiencies of 37.2 lm W–1 for fluorescent devices and 102.7 lm W–1 for phosphorescent devices. These values are significantly higher than those of optimized organic LEDs based on ITO anodes.
1,273 citations
TL;DR: In this article, high efficiency fluorescent organic light-emitting diodes have been realized by employing custom-designed molecules that make it possible to convert non-radiative triplet states into radiative singlet states.
Abstract: High-efficiency fluorescent organic light-emitting diodes have been realized by employing custom-designed molecules that make it possible to convert non-radiative triplet states into radiative singlet states.
TL;DR: O'Regan and Gratzel demonstrated that a film of titania nanoparticles deposited on a DSC would act as a mesoporous n-type photoanode and thereby increase the available surface area for dye attachment by a factor of more than a thousand.
Abstract: Dye-sensitized solar cells (DSCs) are attractive because they are made from cheap materials that do not need to be highly purified and can be printed at low cost 1 . DSCs are unique compared with almost all other kinds of solar cells in that electron transport, light absorption and hole transport are each handled by different materials in the cell 2,3 . The sensitizing dye in a DSC is anchored to a wide-bandgap semiconductor such as TiO2, SnO2 or ZnO. When the dye absorbs light, the photoexcited electron rapidly transfers to the conduction band of the semiconductor, which carries the electron to one of the electrodes 4 . A redox couple, usually comprised of iodide/triiodide (I – /I3 – ), then reduces the oxidized dye back to its neutral state and transports the positive charge to the platinized counter-electrode 5 . In 1991, O’Regan and Gratzel demonstrated that a film of titania (TiO2) nanoparticles deposited on a DSC would act as a mesoporous n-type photoanode and thereby increase the available surface area for dye attachment by a factor of more than a thousand 1 . This approach dramatically improved light absorption and brought power-conversion efficiencies into a range that allowed the DSC to be viewed as a serious competitor to other solar cell technologies 6 . A schematic and energy level diagram showing the operation of a typical DSC is shown in Fig. 1. During the 1990s and the early 2000s, researchers found that organometallic complexes based on ruthenium provided the highest power-conversion efficiencies 7,8
TL;DR: In this paper, the authors discuss the emerging field of mid-infrared frequency comb generation, including technologies based on novel laser gain media, nonlinear frequency conversion and micro-resonators.
Abstract: This Review discusses the emerging field of mid-infrared frequency comb generation, including technologies based on novel laser gain media, nonlinear frequency conversion and microresonators, as well as the applications of these combs in precision spectroscopy and direct frequency comb spectroscopy. Laser frequency combs are coherent light sources that emit a broad spectrum of discrete, evenly spaced narrow lines whose absolute frequency can be measured to within the accuracy of an atomic clock. Their development in the near-infrared and visible domains has revolutionized frequency metrology while also providing numerous unexpected opportunities in other fields such as astronomy and attosecond science. Researchers are now exploring how to extend frequency comb techniques to the mid-infrared spectral region. Versatile mid-infrared frequency comb generators based on novel laser gain media, nonlinear frequency conversion or microresonators promise to significantly expand the applications of frequency combs. In particular, novel approaches to molecular spectroscopy in the 'fingerprint region', with dramatically improved precision, sensitivity, recording time and/or spectral bandwidth may lead to new discoveries in the various fields relevant to molecular science.
TL;DR: By considering a resonator lattice in which the coupling constants between the resonators are harmonically modulated in time and by controlling the spatial distribution of the modulation phases, the authors introduced a scheme that can generate an effective magnetic field for photons, without the use of magneto-optical effects.
Abstract: By considering a resonator lattice in which the coupling constants between the resonators are harmonically modulated in time and by controlling the spatial distribution of the modulation phases, scientists introduce a scheme that can generate an effective magnetic field for photons, without the use of magneto-optical effects.
TL;DR: A highly strained ultrathin membrane of MoS2 could lead to the creation of a solar funnel, a new form of solar cell which absorbs a much broader range of the solar spectrum that a usual single junction device as discussed by the authors.
Abstract: A highly strained ultrathin membrane of MoS2 could lead to the creation of a solar funnel, a new form of solar cell which absorbs a much broader range of the solar spectrum that a usual single junction device.
TL;DR: In this article, a review summarizes the different rare-earth cations and host materials used in mid-infrared fiber laser technology, and discusses the future applications and challenges for the field.
Abstract: Fibre lasers in the mid-infrared regime are useful for a diverse range of fields, including chemical and biomedical sensing, military applications and materials processing. This Review summarizes the different rare-earth cations and host materials used in mid-infrared fibre laser technology, and discusses the future applications and challenges for the field.
TL;DR: In this article, the authors proposed a plasmonic structure for next-generation modern biosensors, which allows a high density of independent subwavelength sensor elements to be constructed in micrometre-sized arrays and is relatively straightforward to integrate those sensors into microfluidics chips.
Abstract: Confinement and enhancement of light by plasmonics allows a high density of independent subwavelength sensor elements to be constructed in micrometre-sized arrays. It is relatively straightforward to integrate those sensors into microfluidics chips, making plasmonic structures promising for use in next-generation modern biosensors.
TL;DR: In this paper, a high-efficiency polymer solar cell whose device architecture is compatible with a large-scale roll-to-roll process is demonstrated, achieving power conversion efficiency of around 7.4%.
Abstract: Researchers demonstrate a high-efficiency polymer solar cell whose device architecture is compatible with a large-scale roll-to-roll process. Enhanced charge collection in the inverted polymer solar cell design and certified power conversion efficiencies of around 7.4% are reported.
TL;DR: In this article, an organic near-infrared dye is used as an antenna for the b-NaYF4:Yb,Er nanoparticles in which the upconversion occurs.
Abstract: Photon upconversion of near-infrared photons is a promising way to overcome the Shockley–Queisser efficiency limit of 32% of a single-junction solar cell. However, the practical applicability of the most efficient known upconversion materials at moderate light intensities is limited by their extremely weak and narrowband near-infrared absorption. Here, we introduce the concept of an upconversion material where an organic near-infrared dye is used as an antenna for the b-NaYF4:Yb,Er nanoparticles in which the upconversion occurs. The overall upconversion by the dye-sensitized nanoparticles is dramatically enhanced (by a factor of ∼3,300) as a result of increased absorptivity and overall broadening of the absorption spectrum of the upconverter. The proposed concept can be extended to cover any part of the solar spectrum by using a set of dye molecules with overlapping absorption spectra acting as an extremely broadband antenna system, connected to suitable upconverters.
TL;DR: In this paper, the FERMI free-electron laser operating in the high-gain harmonic generation regime was demonstrated, allowing high stability, transverse and longitudinal coherence and polarization control.
Abstract: Researchers demonstrate the FERMI free-electron laser operating in the high-gain harmonic generation regime, allowing high stability, transverse and longitudinal coherence and polarization control.
TL;DR: Exploiting the low spatial coherence of specifically designed random lasers, researchers demonstrate speckle-free full-field imaging in the regime of intense optical scattering.
Abstract: Exploiting the low spatial coherence of specifically designed random lasers, researchers demonstrate speckle-free full-field imaging in the regime of intense optical scattering. Their results show that the quality of images generated from random-laser illumination is superior to those generated from spatially coherent illumination.
TL;DR: In this article, the compensation of loss and amplification of surface plasmons in waveguides and resonators is discussed, and future challenges, including how to overcome the large losses present in plasmonic systems that offer strong electromagnetic confinement, are also discussed.
Abstract: This Review provides an introduction to the compensation of loss and amplification of surface plasmons in waveguides and resonators. Future challenges, including how to overcome the large losses present in plasmonic systems that offer strong electromagnetic confinement, are also discussed.
TL;DR: In this paper, the authors proposed a solution-processed semiconductor nanoparticles (quantum dot) for solar cells based on colloidal quantum dots (CQDs) for full-spectrum solar harvesting, which can address the urgent need for low-cost, high-efficiency photovoltaics.
Abstract: Solar cells based on solution-processed semiconductor nanoparticles — colloidal quantum dots — have seen rapid advances in recent years. By offering full-spectrum solar harvesting, these cells are poised to address the urgent need for low-cost, high-efficiency photovoltaics.
TL;DR: In this article, the authors demonstrate a new resonator with a record Q-factor of 875 million for on-chip devices, which sets a new benchmark for the Q factor on a chip, and also provides full compatibility of this important device class with conventional semiconductor processing.
Abstract: Ultrahigh-Q optical resonators are being studied across a wide range of fields, including quantum information, nonlinear optics, cavity optomechanics and telecommunications. Here, we demonstrate a new resonator with a record Q-factor of 875 million for on-chip devices. The fabrication of our device avoids the requirement for a specialized processing step, which in microtoroid resonators8 has made it difficult to control their size and achieve millimetre- and centimetre-scale diameters. Attaining these sizes is important in applications such as microcombs and potentially also in rotation sensing. As an application of size control, stimulated Brillouin lasers incorporating our device are demonstrated. The resonators not only set a new benchmark for the Q-factor on a chip, but also provide, for the first time, full compatibility of this important device class with conventional semiconductor processing. This feature will greatly expand the range of possible ‘system on a chip’ functions enabled by ultrahigh-Q devices.
TL;DR: Based on observations in crystalline MgF2 and planar Si3N4 microresonators, the authors revealed that the existence of multiple and broad-beat notes in a Kerr-frequency comb is due to the formation dynamics of the comb itself.
Abstract: Based on observations in crystalline MgF2 and planar Si3N4 microresonators, scientists reveal that the existence of multiple and broad-beat notes in a Kerr-frequency comb is due to the formation dynamics of the comb itself This work identifies the conditions requires for low-phase-noise performance and also helps to elucidate a number of yet-unexplained phenomena
TL;DR: The intermediate-band solar cell is designed to provide a large photogenerated current while maintaining a high output voltage as mentioned in this paper, and various alloys have been employed in the practical implementation of these devices.
Abstract: The intermediate-band solar cell is designed to provide a large photogenerated current while maintaining a high output voltage. Nanostructured materials and certain alloys have been employed in the practical implementation of these devices. This Progress Article reviews the range of different approaches and discusses how to resolve the remaining technical issues.
TL;DR: In this article, a single-crystal silicon system that offers a fractional frequency instability of 1 × 10−16 at short timescales and supports a laser linewidth of less than 40 mHz at 1.5 µm is presented.
Abstract: Frequency stabilization in a high-finesse optical cavity is limited fundamentally by thermal-noise-induced cavity length fluctuations. Scientists have now developed a single-crystal silicon system that offers a fractional frequency instability of 1 × 10−16 at short timescales and supports a laser linewidth of less than 40 mHz at 1.5 µm.
TL;DR: In this paper, an optomechanical accelerometer that makes use of ultrasensitive displacement readout using a photonic-crystal nanocavity monolithically integrated with a nanotethered test mass of high mechanical Q-factor is presented.
Abstract: The monitoring of acceleration is essential for a variety of applications ranging from inertial navigation to consumer electronics. Typical accelerometer operation involves the sensitive displacement measurement of a flexibly mounted test mass, which can be realized using capacitive, piezo-electric, tunnel-current or optical methods. Although optical detection provides superior displacement resolution, resilience to electromagnetic interference and long-range readout, current optical accelerometers either do not allow for chip-scale integration or utilize relatively bulky test mass sensors of low bandwidth. Here, we demonstrate an optomechanical accelerometer that makes use of ultrasensitive displacement readout using a photonic-crystal nanocavity monolithically integrated with a nanotethered test mass of high mechanical Q-factor This device achieves an acceleration resolution of 10 µg Hz^(−1/2) with submilliwatt optical power, bandwidth greater than 20 kHz and a dynamic range of greater than 40 dB. Moreover, the nanogram test masses used here allow for strong optomechanical backaction, setting the stage for a new class of motional sensors.
TL;DR: In this article, the first half of the magnetic undulator was used to seed the second half via a diamond-based monochromator at angstrom wavelengths, which is a technique similar to ours.
Abstract: Lasing in a hard-X-ray free-electron laser is typically seeded from noise due to the self-amplification of spontaneous emission, which limits temporal coherence and spectral characteristics. Researchers now demonstrate self-seeding using X-rays from the first half of the magnetic undulator to seed the second half via a diamond-based monochromator at angstrom wavelengths.
TL;DR: In this article, wavefront shaping enables real-time widefield imaging through turbid layers with both coherent and incoherent llumination, but also the imaging of objects outside the line-of-sight using light scattered from diffuse walls.
Abstract: Researchers show that wavefront shaping enables not only real-time widefield imaging through turbid layers with both coherent and incoherent llumination, but also the imaging of objects outside the line-of-sight using light scattered from diffuse walls.