Showing papers by "Shuit-Tong Lee published in 2016"
TL;DR: A simple, low-cost blade-coating method is developed for the large-area fabrication of single-crystalline aligned CH3NH3PbI3 microwire (MW) arrays, enabling the fabrication of MW-array-based photodetectors with excellent long-term stability, flexibility, and bending durability.
Abstract: A simple, low-cost blade-coating method is developed for the large-area fabrication of single-crystalline aligned CH3NH3PbI3 microwire (MW) arrays. The solution-coating method is applicable to flexible substrates, enabling the fabrication of MW-array-based photodetectors with excellent long-term stability, flexibility, and bending durability. Integrated devices from such photodetectors demonstrate high performance for high-resolution, flexible image sensors.
318 citations
TL;DR: An improved carburization method is developed and successfully prepared ultrasmall and phase-pure W2C nanoparticles, which enable highly active and sustainable solar-driven hydrogen production and highlight the great potential of this traditionally non-popular material in HER electrocatalysis.
Abstract: Earlier research has been primarily focused on WC as one of the most promising earth-abundant electrocatalysts for hydrogen evolution reaction (HER), whereas the other compound in this carbide family—W2C—has received far less attention. Our theoretical calculations suggest that such a focus is misplaced and W2C is potentially more HER-active than WC. Nevertheless, the preparation of phase pure and sintering-free W2C nanostructures represents a formidable challenge. Here we develop an improved carburization method and successfully prepare ultrasmall and phase-pure W2C nanoparticles. When evaluated for HER electrocatalysis, W2C nanoparticles exhibit a small onset overpotential of 50 mV, a Tafel slope of 45 mV dec−1 and outstanding long-term cycling stability, which are dramatically improved over all existing WC-based materials. In addition, the integration of W2C nanoparticles with p-type Si nanowires enables highly active and sustainable solar-driven hydrogen production. Our results highlight the great potential of this traditionally non-popular material in HER electrocatalysis. Tungsten carbide has yet to live up to its long-believed potential as a replacement for precious metal electrocatalysts. Here, Li and co-workers demonstrate that ditungsten carbide in the form of ultrasmall, phase-pure nanoparticles is a better candidate for the hydrogen evolution reaction.
317 citations
TL;DR: The successful preparation of high-quality topological insulator Bi2Se3/Si heterostructure having an atomically abrupt interface by van der Waals epitaxy growth of Bi2 Se3 films on Si wafer is reported.
Abstract: As an exotic state of quantum matter, topological insulators have promising applications in new-generation electronic and optoelectronic devices. The realization of these applications relies critically on the preparation and properties understanding of high-quality topological insulators, which however are mainly fabricated by high-cost methods like molecular beam epitaxy. We here report the successful preparation of high-quality topological insulator Bi2Se3/Si heterostructure having an atomically abrupt interface by van der Waals epitaxy growth of Bi2Se3 films on Si wafer. A simple, low-cost physical vapor deposition (PVD) method was employed to achieve the growth of the Bi2Se3 films. The Bi2Se3/Si heterostructure exhibited excellent diode characteristics with a pronounced photoresponse under light illumination. The built-in potential at the Bi2Se3/Si interface greatly facilitated the separation and transport of photogenerated carriers, enabling the photodetector to have a high light responsivity of 24.2...
276 citations
TL;DR: It is shown that the composite catalyst chosen is stable with better hydrogen evolution activity than rhodium nanoparticles and even exceeding those of commercial platinum/carbon at high overpotentials, and reveals that silicon plays a key role in the electrocatalysis.
Abstract: Currently, platinum-based electrocatalysts show the best performance for hydrogen evolution. All hydrogen evolution reaction catalysts should however obey Sabatier's principle, that is, the adsorption energy of hydrogen to the catalyst surface should be neither too high nor too low to balance between hydrogen adsorption and desorption. To overcome the limitation of this principle, here we choose a composite (rhodium/silicon nanowire) catalyst, in which hydrogen adsorption occurs on rhodium with a large adsorption energy while hydrogen evolution occurs on silicon with a small adsorption energy. We show that the composite is stable with better hydrogen evolution activity than rhodium nanoparticles and even exceeding those of commercial platinum/carbon at high overpotentials. The results reveal that silicon plays a key role in the electrocatalysis. This work may thus open the door for the design and fabrication of electrocatalysts for high-efficiency electric energy to hydrogen energy conversion.
247 citations
TL;DR: In this article, a simple dip-coating method has been reported to effectively fabricate large-area uniform films of OHP-QDs, which can be used for low-cost display, lighting, and optical communication applications.
Abstract: Organometal halide perovskites quantum dots (OHP-QDs) with bright, color-tunable, and narrow-band photoluminescence have significant advantages in display, lighting, and laser applications. Due to sparse concentrations and difficulties in the enrichment of OHP-QDs, production of large-area uniform films of OHP-QDs is a challenging task, which largely impedes their use in electroluminescence devices. Here, a simple dip-coating method has been reported to effectively fabricate large-area uniform films of OHP-QDs. Using this technique, multicolor OHP-QDs light-emitting diodes (OQ-LEDs) emitting in blue, blue-green, green, orange, and red color have been successfully produced by simply tuning the halide composition or size of QDs. The blue, green, and red OQ-LEDs exhibited, respectively, a maximum luminance of 2673, 2398, and 986 cd m−2 at a current efficiency of 4.01, 3.72, and 1.52 cd A−1, and an external quantum efficiency of 1.38%, 1.06%, and 0.53%, which are much better than most LEDs based on OHP films. The packaged OQ-LEDs show long-term stability in air (humidity ≈50%) for at least 7 d. The results demonstrate the great potential of the dip-coating method to fabricate large-area uniform films for various QDs. The high-efficiency OQ-LEDs also demonstrate the promising potential of OHP-QDs for low-cost display, lighting, and optical communication applications.
223 citations
TL;DR: Cux Co1-x O nanoparticles (NPs) facilely deposited on graphene oxide (GO) is reported as a low-cost and high-performance catalyst for the hydrolysis of AB, which exhibits an initial total turnover frequency (TOF) value of 70.0 mol/(Cat-metal) mol⋅min, which is the highest TOF ever reported for noble metal-free catalysts.
Abstract: Ammonia-borane (AB) is an excellent material for chemical storage of hydrogen. However, the practical utilization of AB for production of hydrogen is hindered by the need of expensive noble metal-based catalysts. Here, we report Cux Co1-x O nanoparticles (NPs) facilely deposited on graphene oxide (GO) as a low-cost and high-performance catalyst for the hydrolysis of AB. This hybrid catalyst exhibits an initial total turnover frequency (TOF) value of 70.0 (H2 ) mol/(Cat-metal) mol⋅min, which is the highest TOF ever reported for noble metal-free catalysts, and a good stability keeping 94 % activity after 5 cycles. Synchrotron radiation-based X-ray absorption spectroscopy (XAS) investigations suggested that the high catalytic performance could be attributed to the interfacial interaction between Cux Co1-x O NPs and GO. Moreover, the catalytic hydrolysis mechanism was studied by in situ XAS experiments for the first time, which reveal a significant water adsorption on the catalyst and clearly confirm the interaction between AB and the catalyst during hydrolysis.
180 citations
TL;DR: The microcavity effect and surface plasmonic loss can be remarkably reduced in white flexible OLEDs, resulting in a substantial increase in the external quantum efficiency and power efficiency to 47.2% and 112.4 lm W(-1).
Abstract: Flexible organic light-emitting diodes (OLEDs) hold great promise for future bendable display and curved lighting applications. One key challenge of high-performance flexible OLEDs is to develop new flexible transparent conductive electrodes with superior mechanical, electrical, and optical properties. Herein, an effective nanostructured metal/dielectric composite electrode on a plastic substrate is reported by combining a quasi-random outcoupling structure for broadband and angle-independent light outcoupling of white emission with an ultrathin metal alloy film for optimum optical transparency, electrical conduction, and mechanical flexibility. The microcavity effect and surface plasmonic loss can be remarkably reduced in white flexible OLEDs, resulting in a substantial increase in the external quantum efficiency and power efficiency to 47.2% and 112.4 lm W–1.
95 citations
TL;DR: A reversible and precise self-assembly of nanoparticles through a linker-free and fast approach by manipulating the interparticle forces, e.g., van der Waals (VDW) force and electrostatic force is reported.
Abstract: Reversible self-assembly of nanoparticles into ordered structures is essential for both fundamental study and practical applications. Although extensive work has been conducted, the demand for simple, cheap, reversible, and versatile ordering methods is still a central issue in current nanoscience and nanotechnology. Here we report a reversible and precise self-assembly of nanoparticles through a linker-free and fast approach by manipulating the interparticle forces, e.g., van der Waals (VDW) force and electrostatic force. Because VDW force is nondirectional, an oriented interaction is achieved to induce the directional binding of nanoparticles utilizing the Janus nanostructure. An effective sol–gel approach has been developed to synthesize metal-organosilica Janus nanoparticles. Dimers and trimers can be obtained by tuning the steric hindrance. After assembly, “hot-spots” can be generated between adjacent nanoparticles, and dramatic enhancement has been observed in surface-enhanced Raman scattering. The ...
88 citations
TL;DR: Li et al. as mentioned in this paper developed a simple and effective method to suppress charge recombination as well as enhancing adhesion force between nanostructured Si and organics by incorporating a silane chemical, namely 3-glycidoxypropyltrimethoxydsilane (GOPS).
Abstract: Nanostructured silicon (Si) can provide improved light harvest efficiencies in organic-Si heterojunction solar cells due to its low light reflection ratio compared with planar one. However, the associated large surface/volume ratio of nanostructured Si suffers from serious surface recombination as well as poor adhesion with organics in organic-Si heterojunction solar cells, which leads to an inferior open-circuit voltage (Voc). Here, we develop a simple and effective method to suppress charge recombination as well as enhancing adhesion force between nanostructured Si and organics by incorporating a silane chemical, namely 3-glycidoxypropyltrimethoxydsilane (GOPS). GOPS can chemically graft onto nanostructured Si and improve the aqueous organic wetting properties, suppressing surface charge recombination velocity dramatically. In addition, this chemically grafted layer can enhance adhesion force between organics and Si. In such a way, a record Voc of 640 mV associated with a power conversion efficiency of 14.1% is obtained for organic-nanostructured Si heterojunction devices. These findings suggest a promising approach to low-cost and simple fabrication for high-performance organic-Si solar cells.
84 citations
TL;DR: In this paper, it was demonstrated that carbon nanodots surface-modified with either phosphorus or amidogen can respectively achieve electrocatalytic activity approaching that of the benchmark Pt/C and IrO2/C catalysts for ORR and OER.
Abstract: Efficient, stable, and low-cost electrocatalysts for the oxygen evolution and reduction reactions (OER and ORR) are essential components of energy conversion. Although much progress has been achieved in the development of platinum-based electrocatalysts for ORR and iridium-based electrocatalysts for OER, they are still not yet viable for large-scale commercialization because of the high cost and scanty supply of the noble metals. Here, it is demonstrated that carbon nanodots surface-modified with either phosphorus or amidogen can respectively achieve electrocatalytic activity approaching that of the benchmark Pt/C and IrO2 /C catalysts for ORR and OER. Furthermore, phosphorus (amidogen)-modified carbon nanodots with attached Au nanoparticles exhibit superior ORR (OER) activity better than commercial Pt/C (IrO2/C) catalysts as well as excellent electrochemical stability under visible light.
83 citations
TL;DR: External quantum efficiency spectra, capacitance-voltage, transient photovoltage decay and minority charge carriers life mapping measurements indicated that a quasi p-n junction was built due to the strong inversion effect, resulting in a high Φb and Vbi.
Abstract: Silicon–organic solar cells based on conjugated polymers such as poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) on n-type silicon (n-Si) attract wide interest because of their potential for cost-effectiveness and high-efficiency. However, a lower barrier height (Φb) and a shallow built in potential (Vbi) of Schottky junction between n-Si and PEDOT:PSS hinders the power conversion efficiency (PCE) in comparison with those of traditional p–n junction. Here, a strong inversion layer was formed on n-Si surface by inserting a layer of 1, 4, 5, 8, 9, 11-hexaazatriphenylene hexacarbonitrile (HAT-CN), resulting in a quasi p–n junction. External quantum efficiency spectra, capacitance–voltage, transient photovoltage decay and minority charge carriers life mapping measurements indicated that a quasi p–n junction was built due to the strong inversion effect, resulting in a high Φb and Vbi. The quasi p–n junction located on the front surface region of silicon substrates improved the short wavelen...
TL;DR: The calculated results reveal that g-SiC7 siligraphene is a semiconductor with a direct band gap of 1.13 eV, which can be easily tuned by applying biaxial strain or a perpendicular electric field, thus holding great potential for photovoltaics applications as a light donor material.
Abstract: The SiC7 siligraphene (g-SiC7) is a novel 2D nanomaterial with a graphene-like structure. Based on theoretical calculations, we have systematically investigated the structure, stability, electronic and optical properties of g-SiC7 siligraphene. The calculated results reveal that g-SiC7 siligraphene is a semiconductor with a direct band gap of 1.13 eV, which can be easily tuned by applying biaxial strain or a perpendicular electric field. Such a g-SiC7 siligraphene shows superior sunlight optical absorbance and is better than g-SiC2 siligraphene and single-layer black phosphorus (phosphorene) in near infrared and visible photon ranges, thus holding great potential for photovoltaics applications as a light donor material.
TL;DR: This work reports the first demonstration of plasmonic Cu3-x P NCs as simple, effective, and solution-processed nonlinear absorbers for high-energy Q-switched fiber laser.
Abstract: A new approach to synthesize self-doped colloidal Cu3-x P NCs with controlled size and localized surface plasmon resonance absorption is reported. These Cu3-x P NCs show ultrafast exciton dynamics and huge optical nonlinearities due to plasmonic resonances, which afford the first demonstration of plasmonic Cu3-x P NCs as simple, effective, and solution-processed nonlinear absorbers for high-energy Q-switched fiber laser.
TL;DR: In this article, the authors summarize the recent advances in 2D layered material/Si heterojunctions and their applications in photovoltaic and optoelectronic devices, and the outlook and challenges of 2D-layer material and Si heterojunction for high-performance device applications are presented.
Abstract: As one of the most important semiconductor materials, silicon (Si) has been widely used in current energy and optoelectronic devices, such as solar cells and photodetectors. However, the traditional Si p–n junction solar cells need complicated fabrication processes, leading to the high cost of Si photovoltaic devices. The wide applications of Si-based photodetectors are also hampered by their low sensitivity to ultraviolet and infrared light. Recently, two-dimensional (2D) layered materials have emerged as a new material system with tremendous potential for future energy and optoelectronic applications. The combination of Si with 2D layered materials represents an innovative approach to construct high-performance optoelectronic devices by harnessing the complementary advantages of both materials. In this review, we summarize the recent advances in 2D layered material/Si heterojunctions and their applications in photovoltaic and optoelectronic devices. Finally, the outlook and challenges of 2D layered material/Si heterojunctions for high-performance device applications are presented.
TL;DR: Though the absorbance of the new catalyst in the visible range of 500-600 nm is much larger than that of the C3N4-CDot catalyst, its water splitting efficiency is much lower, adding insight into and assisting in the further optimization of this new class of photocatalysts to meet the requirements of commercial water splitting systems.
Abstract: A novel C3N4–CDot composite photocatalyst was very recently shown to be highly efficient and very stable in water splitting by solar radiation without using any sacrificial reagent (J. Liu, et al., Science, 2015, 347(6225), 970). This photocatalyst utilizes a two-electron/two-step process in which the production of H2O2 and H2 is photocatalyzed by using C3N4 in the first step and H2O2 is decomposed by using CDots in the second step. The present work is a study on the generality of this approach by application of a C3N4/MnO2 catalyst. This new catalyst indeed splits water by a two step process in a stable way, without any sacrificial agent. It was however found that though the absorbance of the new catalyst in the visible range of 500–600 nm is much larger than that of the C3N4–CDot catalyst, its water splitting efficiency is much lower. These findings add insight into and assist in the further optimization of this new class of photocatalysts to meet the requirements of commercial water splitting systems.
TL;DR: By using first-principles density functional theory calculations, this work demonstrated a simple yet efficient way to achieve controlled p-type doping on II-VI nanostructures via surface charge transfer doping (SCTD) using high work function transition metal oxides as dopants.
Abstract: Wide band gap II–VI nanostructures are important building blocks for new-generation electronic and optoelectronic devices However, the difficulty of realizing p-type conductivity in these materials via conventional doping methods has severely handicapped the fabrication of p–n homojunctions and complementary circuits, which are the fundamental components for high-performance devices Herein, by using first-principles density functional theory calculations, we demonstrated a simple yet efficient way to achieve controlled p-type doping on II–VI nanostructures via surface charge transfer doping (SCTD) using high work function transition metal oxides such as MoO3, WO3, CrO3, and V2O5 as dopants Our calculations revealed that these oxides were capable of drawing electrons from II–VI nanostructures, leading to accumulation of positive charges (holes injection) in the II–VI nanostructures As a result, Fermi levels of the II–VI nanostructures were shifted toward the valence band regions after surface modificat
TL;DR: A simple Si/poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) heterojunction with large band banding and excellent surface passiviation for efficient PEC conversion is developed, exhibiting the potential to be the next-generation economical photoanode in PEC applications.
Abstract: Silicon (Si) is a good photon absorption material for photoelectrochemical (PEC) conversion. Recently, the relatively low photovoltage of Si-based PEC anode is one of the most significant factors limiting its performance. To achieve a high photovoltage in PEC electrode, both a large barrier height and high-quality surface passivation of Si are indispensable. However, it is still challenging to induce a large band bending and passivate Si surface simultaneously in Si-based PEC photoanodes so far, which hinders their performance. Here, we develop a simple Si/poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) heterojunction with large band banding and excellent surface passiviation for efficient PEC conversion. A chemically modified PEDOT:PSS film acts as both a surface passiviation layer and an effective catalyst simultaneously without sacrificing band bending level. A record photovoltage for Si-based PEC photoanodes as high as 657 mV is achieved via optimizing the PEDOT:PSS film fabrication ...
TL;DR: Wang et al. as discussed by the authors pointed out that farsighted research policies, comprehensive research platforms, talent programmes and huge domestic markets are the impetuses for the fast progress of China's research in materials science.
Abstract: Far-sighted research policies, comprehensive research platforms, talent programmes and huge domestic markets are the impetuses for the fast progress of China's research in materials science.
TL;DR: Author(s): Chan, Warren WC; Chhowalla, Manish; Glotzer, Sharon; Gogotsi, Yury; Hafner, Jason H; Hammond, Paula T; Hersam, Mark C; Javey, Ali; Kagan, Cherie R; Khademhosseini,Ali; Kotov, Nicholas A; Lee, Shuit-Tong; Li, Yan; Mohwald, Helmuth; Mulvaney, Paul A
Abstract: Author(s): Chan, Warren WC; Chhowalla, Manish; Glotzer, Sharon; Gogotsi, Yury; Hafner, Jason H; Hammond, Paula T; Hersam, Mark C; Javey, Ali; Kagan, Cherie R; Khademhosseini, Ali; Kotov, Nicholas A; Lee, Shuit-Tong; Li, Yan; Mohwald, Helmuth; Mulvaney, Paul A; Nel, Andre E; Nordlander, Peter J; Parak, Wolfgang J; Penner, Reginald M; Rogach, Andrey L; Schaak, Raymond E; Stevens, Molly M; Wee, Andrew TS; Willson, C Grant; Fernandez, Laura E; Weiss, Paul S
TL;DR: A novel and facile chemical reaction route to modulate the crystallization process of luminescent zinc 8-hydroxyquinoline (Znq2) particles is developed.
TL;DR: This work has proposed a convenient electric-field-assisted method to give the nanomaterials new functions, which can be generalized to other materials and found applications in various fields.
Abstract: Abundant disorderly-distributed surface functional groups, such as hydroxyl, carboxyl, ether and amino groups, endow an isolated graphene oxide quantum dot (GOQD) the polar property due to the symmetry breaking, although the aggregated counterparts present no polarization owing to the random orientation. Here, flexible polarized films were fabricated using aggregated GOQDs with the assistance of external electric fields and their polarization was confirmed with the electrostatic force microscopy and polarization-electric field hysteresis loop. Such polarized GOQD films may induce charges under externally applied deformation. Here, we fabricated nanogenerators based on the films, which gave out an average current value of 0.12 μA and an average voltage value of 12 V under a mechanical force of 60 N. This work has proposed a convenient electric-field-assisted method to give the nanomaterials new functions, which can be generalized to other materials and found applications in various fields.
TL;DR: The usage of plasmonic Cu3-x P colloidal nanocrystals as a new type of tunable saturable absorber for the generation of high-energy pulses in a fiber laser is demonstrated.
Abstract: Q. Bao, W. Ma and co-workers demonstrate the usage of plasmonic Cu3-x P colloidal nanocrystals as a new type of tunable saturable absorber for the generation of high-energy pulses in a fiber laser. As described on page 3535, these low-cost, solution-processed, next-generation nonlinear optical materials can be harnessed for applications in signal processing and optical communication.