Showing papers by "Shuit-Tong Lee published in 2014"
TL;DR: In this paper, the authors demonstrate that charge carrier diffusion lengths of two classes of perovskites are both highly sensitive to film processing conditions and optimal processing procedures are critical to preserve the long carrier diffusion length.
Abstract: We demonstrate that charge carrier diffusion lengths of two classes of perovskites, CH3NH3PbI3−x
Cl
x
and CH3NH3PbI3, are both highly sensitive to film processing conditions and optimal processing procedures are critical to preserving the long carrier diffusion lengths of the perovskite films. This understanding, together with the improved cathode interface using bilayer-structured electron transporting interlayers of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM)/ZnO, leads to the successful fabrication of highly efficient, stable and reproducible planar heterojunction CH3NH3PbI3−x
Cl
x
solar cells with impressive power-conversion efficiencies (PCEs) up to 15.9%. A 1-square-centimeter device yielding a PCE of 12.3% has been realized, demonstrating that this simple planar structure is promising for large-area devices.
198 citations
TL;DR: Depositing a thin layer of MoO3 can improve the performance of planar n-Si/organic solar cells by creating an antireflection layer on the front surface as well as inducing an inversion layer in the Si.
Abstract: High reflection and low build-in electrical field hinder the power conversion efficiency (PCE) of planar n-Si/organic solar cells. Depositing a thin layer of MoO3 can improve the performance by creating an antireflection layer on the front surface as well as inducing an inversion layer in the Si. The as-processed device achieves a record PCE of 13.8%.
173 citations
TL;DR: The facile fabrication of three-dimensional silicon/hematite core/shell nanowire arrays decorated with gold nanoparticles (AuNPs) and their potential application for sunlight-driven solar water splitting are reported.
Abstract: We report the facile fabrication of three-dimensional (3D) silicon/hematite core/shell nanowire arrays decorated with gold nanoparticles (AuNPs) and their potential application for sunlight-driven solar water splitting. The hematite and AuNPs respectively play crucial catalytic and plasmonic photosensitization roles, while silicon absorbs visible light and generates high photocurrent. Under simulated solar light illumination, solar water splitting with remarkable efficiency is achieved with no external bias applied. Such a nanocomposite photoanode design offers great promise for unassisted sunlight-driven water oxidation, and further stability and efficiency improvements to the device will lead to exciting prospects for practical solar water splitting and artificial photosynthesis.
167 citations
TL;DR: A flexible transparent conductor on plastic with embedded silver networks which is used to achieve flexible, highly power-efficient large-area green and white OLEDs exhibit a power efficiency of 106 lm W(-1) at 1000 cd m(-2) with angular color stability, which is significantly higher than all other reports of flexiblewhite OLEDs.
Abstract: Because of their mechanical flexibility, organic light-emitting diodes (OLEDs) hold great promise as a leading technology for display and lighting applications in wearable electronics. The development of flexible OLEDs requires high-quality transparent conductive electrodes with superior bendability and roll-to-roll manufacturing compatibility to replace indium tin oxide (ITO) anodes. Here, we present a flexible transparent conductor on plastic with embedded silver networks which is used to achieve flexible, highly power-efficient large-area green and white OLEDs. By combining an improved outcoupling structure for simultaneously extracting light in waveguide and substrate modes and reducing the surface plasmonic losses, flexible white OLEDs exhibit a power efficiency of 106 lm W–1 at 1000 cd m–2 with angular color stability, which is significantly higher than all other reports of flexible white OLEDs. These results represent an exciting step toward the realization of ITO-free, high-efficiency OLEDs for us...
150 citations
TL;DR: In this paper, an efficient white organic light-emitting diodes (OLEDs) were shown that combines deterministic aperiodic nanostructures for broadband quasi-omnidirectional light extraction and a multilayer energy cascade structure for energy-efficient photon generation.
Abstract: Highly power-efficient white organic light-emitting diodes (OLEDs) are still challenging to make for applications in high-quality displays and general lighting due to optical confinement and energy loss during electron-photon conversion. Here, an efficient white OLED structure is shown that combines deterministic aperiodic nanostructures for broadband quasi-omnidirectional light extraction and a multilayer energy cascade structure for energy-efficient photon generation. The external quantum efficiency and power efficiency are raised to 54.6% and 123.4 lm W−1 at 1000 cd m−2. An extremely small roll-off in efficiency at high luminance is also obtained, yielding a striking value of 106.5 lm W−1 at 5000 cd m−2. In addition to a substantial increase in efficiency, this device structure simultaneously offers the superiority of angular color stability over the visible wavelength range compared to conventional OLEDs. It is anticipated that these findings could open up new opportunities to promote white OLEDs for commercial applications.
143 citations
TL;DR: In this article, a novel method of fabricating high-efficiency organic solar cells (OSCs) is proposed using biomimetic moth eye nanostructures in a quasi-periodic gradient shape active layer and an antireflective coating.
Abstract: Advanced light manipulation is extremely attractive for applications in organic optoelectronics to enhance light harvesting efficiency. A novel method of fabricating high-efficiency organic solar cells (OSCs) is proposed using biomimetic moth eye nanostructures in a quasi-periodic gradient shape active layer and an antireflective coating. A 24.3% increase in photocurrent is realized without sacrificing dark electrical properties, yielding a 22.2% enhancement in power conversion efficiency to a record of 7.86% for OSCs with a poly(3-hexylthiophene-2,5-diyl):indene-C60 bis-adduct (P3HT:ICBA) active layer. The experimental and theoretical characterizations verify that the substantial improvement of OSCs is mainly ascribed to the self-enhanced absorption resulting from the broadband polarization-insensitive light trapping in biomimetic nanostructured active layer, the reduction in reflectance by the antireflective coating, and surface plasmonic effect excited by corrugated metallic electrode. It is noteworthy that the pathway described here is promising for opening up opportunities to realize high-performance OSCs towards the future photovoltaic applications.
107 citations
103 citations
TL;DR: The use of 5-10 nm CQDs as a light responsive and controllable photocatalyst is truly a novel application of carbon-based nanomaterials, which may significantly push research in the current catalytic industry, environmental pollution and energy issues.
Abstract: Developing light-driven acid catalyst will be very meaningful for the controlled-acid catalytic processes towards a green chemical industry. Here, based on scanning electrochemical microscopy (SECM) and ΔpH testing, we demonstrate that the 5-10 nm carbon quantum dots (CQDs) synthesized by electrochemical ablation of graphite have strong light-induced proton properties under visible light in solution, which can be used as an acid catalyst. The 5-10 nm CQDs' catalytic activity is strongly dependent on the illumination intensity and the temperature of the reaction system. As an effective visible light driven and controlled acid-catalyst, 5-10 nm CQDs can catalyze a series of organic reactions (esterification, Beckmann rearrangement and aldol condensation) with high conversion (34.7-46.2%, respectively) in water solution under visible light, while the 1-4 nm CQDs and 10-2000 nm graphite do not have such excellent catalytic activity. The use of 5-10 nm CQDs as a light responsive and controllable photocatalyst is truly a novel application of carbon-based nanomaterials, which may significantly push research in the current catalytic industry, environmental pollution and energy issues.
91 citations
TL;DR: The representative achievements related to the design of high-performance silicon nanohybrid-based SERS sensors and their use for chemical and biological analysis are reviewed in a detailed way.
Abstract: Nanomaterial-based surface-enhanced Raman scattering (SERS) sensors are highly promising analytical tools, capable of ultrasensitive, multiplex, and nondestructive detection of chemical and biological species. Extensive efforts have been made to design various silicon nanohybrid-based SERS substrates such as gold/silver nanoparticle (NP)-decorated silicon nanowires, Au/Ag NP-decorated silicon wafers (AuNP@Si), and so forth. In comparison to free AuNP- and AgNP-based SERS sensors, the silicon nanohybrid-based SERS sensors feature higher enhancement factors (EFs) and excellent reproducibility, since SERS hot spots are efficiently coupled and stabilized through interconnection to the semiconducting silicon substrates. Consequently, in the past decade, giant advancements in the development of silicon nanohybrid-based SERS sensors have been witnessed for myriad sensing applications. In this review, the representative achievements related to the design of high-performance silicon nanohybrid-based SERS sensors and their use for chemical and biological analysis are reviewed in a detailed way. Furthermore, the major opportunities and challenges in this field are discussed from a broad perspective and possible future directions.
64 citations
TL;DR: It is shown that the modified UMG silicon surface can increase the minority carrier lifetime because of reduced impurity and surface area, and a design rule for an efficient silicon solar cell with low-quality silicon absorbers is suggested.
Abstract: Low-quality silicon such as upgraded metallurgical-grade (UMG) silicon promises to reduce the material requirements for high-performance cost-effective photovoltaics. So far, however, UMG silicon currently exhibits the short diffusion length and serious charge recombination associated with high impurity levels, which hinders the performance of solar cells. Here, we used a metal-assisted chemical etching (MACE) method to partially upgrade the UMG silicon surface. The silicon was etched into a nanostructured one by the MACE process, associated with removing impurities on the surface. Meanwhile, nanostructured forms of UMG silicon can benefit improved light harvesting with thin substrates, which can relax the requirement of material purity for high photovoltaic performance. In order to suppress the large surface recombination due to increased surface area of nanostructured UMG silicon, a post chemical treatment was used to decrease the surface area. A solution-processed conjugated polymer of poly(3,4-ethylen...
61 citations
TL;DR: The quantitative data on the permeability of the HeLa cell membrane in the presence of CQDs with different surface functional groups is provided, which are valuable for promoting the bio-applications of carbon nanostructures in living systems.
Abstract: The interaction between carbon quantum dots (CQDs) and a single living cell was explored in real time. Here, we provide the quantitative data on the permeability of the HeLa cell membrane in the presence of CQDs with different surface functional groups (CQDs terminated with –OH/–COOH (CQD–OH), –PEG (CQD–PEG), and –NH2 (CQD–NH2)). Although these CQDs have very low toxicity towards HeLa cells, they still increase the cell membrane permeability by 8%, 13%, and 19% for CQD–PEG, CQD–OH, and CQD–NH2, respectively, and this kind of permeability was irreversible. These observations are valuable for promoting the bio-applications of carbon nanostructures in living systems.
TL;DR: Compared to MCEE commonly performed in aqueous HF solution, the present pseudo gas phase etching offers exceptional simplicity, flexibility, environmental friendliness, and scalability for the fabrication of three-dimensional silicon nanostructures with considerable depths.
Abstract: Inspired by metal corrosion in air, we demonstrate that metal-catalyzed electroless etching (MCEE) of silicon can be performed simply in aerated HF/H2O vapor for facile fabrication of three-dimensional silicon nanostructures such as silicon nanowires (SiNW) arrays. Compared to MCEE commonly performed in aqueous HF solution, the present pseudo gas phase etching offers exceptional simplicity, flexibility, environmental friendliness, and scalability for the fabrication of three-dimensional silicon nanostructures with considerable depths because of replacement of harsh oxidants such as H2O2 and AgNO3 by environmental-green and ubiquitous oxygen in air, minimum water consumption, and full utilization of HF.
TL;DR: Investigation reveals that LUMO energy is a helpful aid in predicting the alkaline stability of imidazolium cations and indicates that alkyl groups are the most suitable substituents for the N3 position of imdazolia cations.
Abstract: Imidazolium cations are promising candidates for preparing anion-exchange membranes because of their good alkaline stability. Substitution of imidazolium cations is an efficient way to improve their alkaline stability. By combining density functional theory calculations with experimental results, it is found that the LUMO energy correlates with the alkaline stability of imidazolium cations. The results indicate that alkyl groups are the most suitable substituents for the N3 position of imidazolium cations, and the LUMO energies of alkyl-substituted imidazolium cations depend on the electron-donating effect and the hyperconjugation effect. Comparing 1,2-dimethylimidazolium cations (1,2-DMIm+) and 1,3-dimethylimidazolium cations (1,3-DMIm+) with the same substituents reveals that the hyperconjugation effect is more significant in influencing the LUMO energy of 1,3-DMIms. This investigation reveals that LUMO energy is a helpful aid in predicting the alkaline stability of imidazolium cations.
TL;DR: Macroscopic galvanic cell-driven metal catalyzed electroless etching of silicon in aqueous hydrofluoric acid (HF) solution is devised to fabricate silicon nanowire arrays with dissolved oxygen acting as the one and only oxidizing agent.
Abstract: Macroscopic galvanic cell-driven metal catalyzed electroless etching (MCEE) of silicon in aqueous hydrofluoric acid (HF) solution is devised to fabricate silicon nanowire (SiNW) arrays with dissolved oxygen acting as the one and only oxidizing agent. The key aspect of this strategy is the use of a graphite or other noble metal electrode that is electrically coupled with silicon substrate.
TL;DR: These GO substrates exhibited excellent biocompatibility and enabled effective gene transfection for various cell lines including stem cells, thus promising important applications in stem cell research and tissue engineering.
Abstract: A facile approach was developed to fabricate patterned substrates of nano-graphene oxide, demonstrating highly localized and efficient gene delivery to multiple cell lines in a substrate-mediated manner. The GO substrates served as a valid platform to preconcentrate PEI/pDNA complexes and maintain their gradual releasing for a relatively long period of time. Our approach allowed successful gene delivery in selected groups of cells on the stripe-patterned GO substrates, without transfecting their neighbor cells directly cultured on glass. These GO substrates exhibited excellent biocompatibility and enabled effective gene transfection for various cell lines including stem cells, thus promising important applications in stem cell research and tissue engineering.
TL;DR: In this article, the influence of constituent materials and the operational stability of charge generation layers (CGLs) on the device characteristics of tandem organic light-emitting diodes (OLEDs) is reported upon.
Abstract: The influence of constituent materials and the operational stability of charge generation layers (CGLs) on the device characteristics of tandem organic light-emitting diodes (OLEDs) is reported upon. The CGLs between two vertically stacked emission units consist of an abrupt heterointerface between a MoO3 film and an n-type doped organic electron-transporting layer, where the n-type dopants vary from reactive metal (Mg) to metallic compounds (i.e., Cs2CO3 and CsN3). Contrary to the almost identical electron injection barriers modulated by the n-type dopants, the device characteristics and operational stability of tandem OLEDs are found to be sensitive to the doping constituent materials used in the CGLs. Using data on the electrical and spectral emission properties, electronic structures and the lifetime characteristics, it is identified that the degradation of the n-type doped layers in CGLs provides the main contribution to the device lifetime, due to the different doping mechanisms.
TL;DR: A facile approach of layer-by-layer-assembled MFNPs conjugated with monoclonal antibody anti-HER2 demonstrates the specific detection of breast cancer BT474 cells (biomarker HER2 positive) with a high signal-to-noise ratio.
Abstract: There is a great need to develop multifunctional nanoparticles (MFNPs) for cancer biomarker-based detection and highly selective therapeutic treatment simultaneously. Here we describe a facile approach of layer-by-layer-assembled MFNPs conjugated with monoclonal antibody anti-HER2, demonstrating the specific detection of breast cancer BT474 cells (biomarker HER2 positive) with a high signal-to-noise ratio. The MFNPs contain a well-defined core–shell structure of UCNP@Fe3O4@Au coated by poly(ethylene glycol) (PEG) and anti-HER2 antibody, displaying excellent dispersity in various aqueous solutions. This unique combination of nanoparticles and ligand molecules allows us to perform photothermal treatment (PTT) of the cancer cells, while simultaneously quantifying the distribution of MFNPs on a cancer cell surface induced by antigen–antibody binding events. An important finding is that cancer cells adjacent to each other or in physical proximity within micrometers may end up with different fates of survival o...
TL;DR: In this paper, a solution-processed mixture of Au nanoparticles (NPs) and MoOX as an inter-layer in organic light-emitting devices (OLEDs), leading to the enhanced light emission and good stability.
TL;DR: It is demonstrated that oxygen vacancies, which are common in TiO2, accelerate nonradiative energy losses by an order of magnitude and rationalize the unforeseen experimental observations and provide the atomistic basis for improving the structure and charge transport byTiO2 nanotubes.
Abstract: Highly ordered TiO2 nanotube arrays can be grown by simple electrochemical anodization of a titanium metal sheet, stimulating intense research and applications to solar cells and fuels. TiO2 nanotubes were expected to exhibit better electron transport than nanocrystal films. However, experiments showed that nanotubes provided little advantage over nanoparticles. Using nonadiabatic molecular dynamics, we demonstrate that oxygen vacancies, which are common in TiO2, accelerate nonradiative energy losses by an order of magnitude. Oxygen vacancies produce localized Ti(3+) states hundreds of millielectronvolts below the TiO2 conduction band. The states lower the nanotube band gap, trap excited electrons, induce stronger electron-phonon couplings, and facilitate the relaxation. Our results rationalize the unforeseen experimental observations and provide the atomistic basis for improving the structure and charge transport by TiO2 nanotubes.
TL;DR: In this paper, a class of single-particle SERS approaches, i.e., reactive ion etching (RIE)-assisted SERS measurements correlated with scanning electron microscopy (SEM) strategy, was developed, enabling precise and high-resolution identification of single gold nanoparticle (AuNP) in facile and reliable manners.
Abstract: Single-nanoparticle surface-enhanced Raman scattering (SERS) measurement is of essential importance for both fundamental research and practical applications. In this work, we develop a class of single-particle SERS approaches, i.e., reactive ion etching (RIE)-assisted SERS measurements correlated with scanning electron microscopy (SEM) strategy (RIE/SERS/SEM), enabling precise and high-resolution identification of single gold nanoparticle (AuNP) in facile and reliable manners. By using AuNP-coated silicon wafer and quartz glass slide as models, we further employ the developed RIE/SERS/SEM method for interrogating the relationship between SERS substrates and enhancement factor (EF) on the single particle level. Together with theoretical calculation using an established finite-difference-time-domain (FDTD) method, we demonstrate silicon wafer as superior SERS substrates, facilitating improvement of EF values.
TL;DR: In this article, the series and shunt resistances of hybrid organic-inorganic hybrid solar cells were tuned to observe its effect on the device performance, and it was found that with suitable substrate scales and physical tailoring methods, the shunt and series resistances can be adjusted to eliminate the unfavorable charge trapping phenomenon.
01 Jan 2014
TL;DR: In this article, the authors discuss the major issues hindering the development of CBN films for practical applications, and review recent progress in the synthesis and characterization of cBN films, in particular, to increase film thickness, improving crystallinity, reducing residual stress, and enhancing adhesion to the substrates.
Abstract: Cubic boron nitride (cBN) is structurally analogous to diamond, with similar or even superior properties for certain applications. Studies on the low-pressure synthesis of cBN films started around 1980. So far a variety of ion-assisted physical vapor deposition and chemical vapor deposition methods to deposit cBN films on various substrates have been developed. This chapter discusses the major issues hindering cBN films for practical applications, and reviews recent progress in the synthesis and characterization of cBN films, in particular, to increase film thickness, improving crystallinity, reducing residual stress, and enhancing adhesion to the substrates. The merits and demerits of different deposition techniques are discussed. Common features and differences in the structures and properties of cBN films deposited by different approaches are described. This chapter also summarizes up-to-date studies on the mechanical, electronic, optoelectronic, and optical properties of cBN films, and presents example applications of cBN films in cutting tools, deep-ultraviolet detectors, and chemical and biological sensors.
TL;DR: Two-dimensional (2D) hexagonal microsheets of 8-hydroxyquinoline zinc (Znq2) were synthesized readily via a mixed solvent induced self-assembly method and the 2D optical waveguiding properties have been clearly revealed by both fluorescence microscopy and confocal microscopy.
TL;DR: In this paper, tungsten carbide (WC) was used as an efficient anode buffer layer for a high-performance inverted organic solar cell, which achieved power conversion efficiencies (PCEs) of 3.83% and 8.04% respectively.
Abstract: We demonstrated tungsten carbide (WC) as an efficient anode buffer layer for a high-performance inverted organic solar cell. The devices based on active layers comprised of either poly(3-hexylthiophene) (P3HT) or poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7) mixed with fullerene derivatives have achieved power conversion efficiencies (PCEs) of 3.83% and 8.04%, respectively. The WC layer was deposited onto the active layer from a surfactant-free nanoparticle alcohol solution because the buffer layer was well functionalized, removing the requirement for oxygen-plasma or annealing treatment, while simultaneously allowing for optimum photogenerated charge-carrier collection in an inverted structure device. The WC-based device displayed an improved stability performance compared with the MoO3-based one. The anode buffer layer introduced here was easy to implement and compatible with solution processed organic photovoltaics, and therefore applicable for potential cost-effective manufacturing processes.
TL;DR: The first example of silicon nanowire (SiNW)-based in vivo tumor phototherapy is presented, with 100% of mice being alive and tumor-free for over 8 months, which is the longest survival time ever reported for tumor-bearing mice treated with nanomaterial-based NIR hyperthermia agents.
Abstract: The first example of silicon nanowire (SiNW)-based in vivo tumor phototherapy is presented. Gold nanoparticle (AuNP)-decorated SiNWs are employed as high-performance NIR hyperthermia agents for highly efficacious in vivo tumour ablation. Significantly, the overall survival time of SiNW-treated mice is drastically prolonged, with 100% of mice being alive and tumor-free for over 8 months, which is the longest survival time ever reported for tumor-bearing mice treated with nanomaterial-based NIR hyperthermia agents.
TL;DR: Author(s): Chan, Warren CW; Gogotsi, Yury; Hafner, Jason H; Hammond, Paula T; Hersam, Mark C; Javey, Ali; Kagan, Cherie R; Kotov, Nicholas A; Lee, Shuit-Tong; Mohwald, Helmuth; Mulvaney, Paul A; Nel, Andre E; Nordlander, Peter J; Parak, Wolfgang J; Penner, Reginald M
Abstract: Author(s): Chan, Warren CW; Gogotsi, Yury; Hafner, Jason H; Hammond, Paula T; Hersam, Mark C; Javey, Ali; Kagan, Cherie R; Khademhosseini, Ali; Kotov, Nicholas A; Lee, Shuit-Tong; 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; Weiss, Paul S
TL;DR: In this paper, the authors constructed a concept of the full-organic carrier collection layer (CCL) used for polymer solar cells, which is composed of dipyrazino[2,3-f:2′,3′-h]quinoxaline and chlorine-free solvents (formic acid) processed 4,7-Diphenyl-1,10-phenanthroline (Bphen) as electron collection layer, exhibiting good solubility and environmental protection.
Abstract: We constructed a concept of the full-organic carrier collection layer (CCL) used for polymer solar cells. The CCL is composed of dipyrazino[2,3-f:2′,3′-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile as hole collection layer (HCL) and chlorine-free solvents (formic acid (FA)) processed 4,7-Diphenyl-1,10-phenanthroline (Bphen) as electron collection layer, exhibiting good solubility, and environmental protection. The FA based device shows ideal power conversion efficiency (3.75%), which is higher than that of control device (3.6%). Besides, the HCL shows a different mechanism in hole extraction by functioning as a charge recombination zone for electrons injected from anode and holes extracted from the donor materials.