Yanjun Guo

A novel BiOCl film with flowerlike hierarchical structures and its optical properties.

A novel BiOCl film with flowerlike hierarchical structures has been fabricated for the first time by dipping Bi film in a mixed solution of H(2)O(2) and HCl. This method presents the advantages of a simple technique, template-free, uniform and controllable morphology, as well as easy mass production. Each flowerlike hierarchical structure is composed of several dozen ultra-thin single-crystal nanopetals which grow along the 110 directions in the tetragonal structure. The layered growth of nanopetals is related to the more marked anion polarization along the c axis and layered stacking of various atoms (Cl-Bi-O-Bi-Cl). The growth mechanism of the BiOCl hierarchical structure is preferred to be a nucleation-dissolution-recrystallization process. A Raman shift originating from laser-induced compressive stress is observed. Photoluminescence (PL) spectra of the BiOCl film show principal green emission, indicating potential applications in optoelectronic devices.

Performance enhancement of perovskite-sensitized mesoscopic solar cells using Nb-doped TiO2 compact layer

Perovskite solar cells are one of the most promising alternatives to conventional photovoltaic devices, and extensive studies are focused on device optimization to further improve their performance. A compact layer of TiO2 is generally used in perovskite solar cells to block holes from reaching the fluorine-doped tin oxide electrode. In this contribution, we engineered a TiO2 compact layer using Nb doping, which resulted in solar cells with a power conversion efficiency (PCE) of 10.26%, which was higher than that of devices with the same configuration but containing a pristine TiO2 compact layer (PCE = 9.22%). The device performance enhancement was attributed to the decreased selective contact resistance and increased charge recombination resistance resulting from Nb doping, which was revealed by the impedance spectroscopy measurements. The developed strategy highlights the importance of interface optimization for perovskite solar cells.

Drastically Enhanced High-Rate Performance of Carbon-Coated LiFePO4 Nanorods Using a Green Chemical Vapor Deposition (CVD) Method for Lithium Ion Battery: A Selective Carbon Coating Process

Application of LiFePO4 (LFP) to large current power supplies is greatly hindered by its poor electrical conductivity (10(-9) S cm(-1)) and sluggish Li+ transport. Carbon coating is considered to be necessary for improving its interparticle electronic conductivity and thus electrochemical performance. Here, we proposed a novel, green, low cost and controllable CVD approach using solid glucose as carbon source which can be extended to most cathode and anode materials in need of carbon coating. Hydrothermally synthesized LFP nanorods with optimized thickness of carbon coated by this recipe are shown to have superb high-rate performance, high energy, and power densities, as well as long high-rate cycle lifetime. For 200 C (18s) charge and discharge, the discharge capacity and voltage are 89.69 mAh g(-1) and 3.030 V, respectively, and the energy and power densities are 271.80 Wh kg(-1) and 54.36 kW kg(-1), respectively. The capacity retention of 93.0%, and the energy and power density retention of 93.6% after 500 cycles at 100 C were achieved. Compared to the conventional carbon coating through direct mixing with glucose (or other organic substances) followed by annealing (DMGA), the carbon phase coated using this CVD recipe is of higher quality and better uniformity. Undoubtedly, this approach enhances significantly the electrochemical performance of high power LFP and thus broadens greatly the prospect of its applications to large current power supplies such as electric and hybrid electric vehicles.

An experimental apparatus for simultaneously measuring Seebeck coefficient and electrical resistivity from 100 K to 600 K.

In this paper, we report a fully automated experimental apparatus for measuring Seebeck coefficient and electrical resistivity of a sample simultaneously in a temperature range of 100-600 K. The Seebeck coefficient is measured using a quasi-steady temperature differential method in which two ceramic heaters are employed to alternately heat the sample. The sample holder is designed to reduce temperature disturbance on its base during a measurement cycle. To demonstrate the accuracy and reliability of the experimental setup, we have performed tests on reference materials including constantan and platinum.

Hydrothermal growth of MoS 2 /Co 3 S 4 composites as efficient Pt-free counter electrodes for dye-sensitized solar cells

MoS2/Co3S4 composite films were prepared via a facile one-step hydrothermal method, and used as efficient and low-cost Pt-free counter electrodes (CEs) for dye-sensitized solar cells (DSSCs). Characterizations revealed that Co3S4 and MoS2 were obtained simultaneously during the facile hydrothermal process. The composites afforded a promising synergistic effect on the catalyzing of triiodide reduction. Enhanced electrocatalytic performance of the resultant composite films was confirmed through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) analyses. DSSCs using MoS2/Co3S4 composite CEs outperform the devices with pristine MoS2 or Co3S4 CEs in power conversion efficiency (PCE). Furthermore, a PCE of 6.77% is obtained for the optimized devices using MoS2/Co3S4 composite CEs measured under standard 1 sun illumination (100 mW cm−2, AM 1.5G), which is comparable to that of the devices fabricated under the same conditions with conventional thermally deposited Pt CEs (7.14%). The results demonstrate that MoS2/Co3S4 composites are promising alternatives to Pt to be applied as CEs for DSSCs.摘要染料敏化太阳电池因其成本低、稳定性好、工艺简便而备受关注. 发展高性能、廉价的材料代替传统的贵金属铂对电极是当前染 料敏化太阳电池领域的研究热点之一. 二硫化钼纳米材料具有高比表面积和大量的催化位点, 是较为理想的铂对电极替代材料之一, 但较 低的电导率限制了二硫化钼对电极性能的进一步提高. 本文首次报道了由二硫化钼纳米材料与金属性的四硫化三钴复合制备染料敏化 太阳电池对电极, 该复合对电极可以利用水热方法一步合成. 研究结果表明, 使用该复合对电极的染料敏化太阳电池光电转换效率可达 6.77%, 接近于使用铂对电极的器件(7.14%), 优于使用单一二硫化钼(4.64%)或四硫化三钴(5.11%)作为对电极的器件.

Very high power and superior rate capability LiFePO4 nanorods hydrothermally synthesized using tetraglycol as surfactant

Small polarizations, i.e. sufficiently good electronic and ionic conductivity is indispensible for high power lithium iron phosphate, especially for its applications to large current power supplies. Here, carbon coated LiFePO4/C nanorods that were hydrothermally synthesized using tetraglycol as surfactant followed by calcination exhibit very small polarizations (13.0 mV at 0.1 C, 1 C = 170 mA g−1), high power densities (96.5 and 95.4 kW kg−1 at 200 C at RT and 60 °C, respectively), and excellent cycling performance at high rates (92% discharge capacity retention at 100 C after 200 cycles) with only 10 wt% conductive additive. Intermixing between Fe and Li is detected in the as-synthesized, annealed and carbon coated samples. The superior rate capabilities (270.0 W h kg−1 and 43.0 kW kg−1 at 85 C at RT, 310 W h kg−1 and 49.8 kW kg−1 at 96 C at 60 °C) and small polarizations are attributed to the nanoscale size along the [010] plane, the uniform carbon coating and the partial occupation of Li at the Fe sites. The recipe in this study is quite simple, controllable, energy saving and readily up-scalable. The availability of very high power LiFePO4 with excellent cycling capability at high rates will undoubtedly greatly promote its applications to large current power supplies such as electric and hybrid electric vehicles.

Measurement of the methemoglobin concentration using Raman spectroscopy

Abstract Methemoglobin concentration is an important pathophysio-logical biomarker, reflecting the oxygen-carrying and oxygen-releasing capabilities of hemoglobin (Hb). Raman spectroscopy is used to develop a novel technique for determining the methemoglobin concentration. Raman activity combined with two-dimensional correlation analysis is an attractive method for investigating Hb oxidation, exhibiting several relevant peaks in the range of 1200–1650 cm− 1. Methemoglobin concentration is estimated by measuring the intensity of Raman peaks in the ranges of 1210–1230 cm− 1 and 1340–1380 cm− 1 with 785-nm excitation. The correlation between Raman-based methemoglobin concentration estimations and the methemoglobin concentration measured using spectrophotometry was highly significant. These results suggest the potential of Raman spectroscopy as a new quantitative approach to determine the methemoglobin concentration.

Study on readout durability of super-RENS disk

Characteristics essential for the readout durability of a superresolution near-field structure (super-RENS) disk are studied experimentally by using a home-built optical measuring setup and atomic force microscope, based on a simplified PtOx super-RENS disk. The experimental results show that for a super-RENS disk with constant structure and materials, readout signals including transmittance and reflectance vary with changes in bubble shape and size, indicating that the readout durability of the disk has a strong dependence on bubble stability, which is closely related to the thickness of the cover layer, the recording power and readout power, and the mechanical properties of the dielectric layer. Based on our experimental results, the main direction for improving readout durability is also proposed.

Ru-Doping in TiO2 electron transport layers of planar heterojunction perovskite solar cells for enhanced performance

TiO2 is widely used as an electron transport layer (ETL) material for perovskite solar cells, and various methods have been used to engineer the properties of TiO2 ETLs for further improving the performance of perovskite solar cells. In this study, compact Ru-doped TiO2 films, prepared via a one-step spray pyrolysis method, have been employed as ETLs for planar perovskite solar cells. Compared to the pristine TiO2 film, the doped counterpart exhibits remarkably improved conductivity, as revealed by the conducting atomic force microscopy measurement. Consequently, the optimized device containing a 1% Ru-doped TiO2 ETL presents a power conversion efficiency (PCE) of up to 15.7% (with an average value of 14.74%), which is 17% higher than that of the device using the pristine TiO2 layer (13.42%, with an average value of 12.20%). The mechanism behind the enhancement in photovoltaic parameters has been investigated intensively via physicochemical characterization. A slight upshift of the conduction band minimum (CBM) is observed in the case of Ru-doped TiO2 films. More importantly, fast injection of the photo-generated electrons from a perovskite layer into an ETL is also found when Ru-doped TiO2 is applied as the ETL. Meanwhile, impedance spectroscopy suggests that the application of Ru-doped TiO2 films leads to an increase in recombination resistance and a decrease in selective contact resistance. The enhancement in PCE is attributed to the improved charge injection and transport properties of the Ru-doped TiO2 film, as well as its better band matching with the perovskite layer. These results demonstrate that doping TiO2 ETLs with Ru is an efficient approach to improve the photovoltaic performance of perovskite solar cells. The presented work will provide a potential approach for developing materials with high-quality electron transport layers for efficient perovskite-based photovoltaic devices.

Thickness-dependent morphologies of Ag on n-layer MoS2 and its surface-enhanced Raman scattering

The size and density of Ag nanoparticles on n-layer MoS2 exhibit thicknessdependent behavior. The size and density of these particles increased and decreased, respectively, with increasing layer number (n) of n-layer MoS2. Furthermore, the surface-enhanced Raman scattering (SERS) of Ag on this substrate was observed. The enhancement factor of this scattering varied with the thickness of MoS2. The mechanisms governing the aforementioned thickness dependences are proposed and discussed.