In this research, hollow Co/NC@NC catalysts were successfully prepared and applied to modify the separator in Lithium-Sulfur (Li-S) system. Among this composite, carbon films from dopamine (DA) carbonation can enhance the electrical conductivity of material, and Co species adsorb lithium polysulfide (LiPSs), paving the way for further catalytic conversion of LiPSs to Li2S, which can greatly limit the shuttle effect. Moreover, the hollow structure not only contributes more active sites, but also promotes the diffusion of Li+, which is significant for the improvement of battery performance. By taking advantage of the coating material components and structure, Li-S cells achieve a high initial capacity (1098 mAh/g at 0.2C), impressive rate performance (640 mAh/g at 2C and 420 mAh/g at 4C), and superior cycling stability (826 mAh/g obtained after 100 cycles at 0.5C).
Tandem devices combining perovskite and silicon solar cells are promising candidates to achieve power conversion efficiencies above 30% at reasonable costs. However, it is rarely reported about the effect of surface recombination on tandem solar cells. In this paper, we analyze the influence of surface recombination on the performance of tandem cells. Simulations show surface recombination can reduce the cell’s open-circuit voltage (Voc), short-circuit current (Jsc), and efficiency. The efficiency of the tandem cell decreases with the increase of the surface recombination rate on the sub cells. The maximum efficiency of the tandem cell without surface recombination is 25.81%. When the recombination velocity of the silicon sub cell increases from 0 to 105 cm/s, the overall efficiency decreases to 13.96%. When the same surface recombination velocity is added to perovskite sub cell, the overall efficiency is 13.89%. When both the surface recombination velocity of perovskite and silicon are 105 cm/s, the efficiency of the tandem cell decreases to 13.42%. Therefore, the performances of the tandem cell are similar in the cases of single sub cell with surface recombination and both sub cells with surface recombination.
KEYWORDS: Absorption, Silicon, Solar cells, Thin film solar cells, Reflectivity, Nanostructures, Thin films, Silicon solar cells, Silicon films, Crystals
The crystalline silicon (c-Si) solar cells with light-trapping structures can enhance light absorption within the semiconductor absorber layer, especially in thin-film crystalline silicon (c-Si) solar cells. Here we demonstrate that a dome surface light-trapping scheme for c-Si thin films, fabricated via laser interference lithography and chemical wet etching process, significantly enhances the light absorption within the c-Si layer. In this paper, we demonstrate its good antireflection ability and light trapping performance. As a result, an overall reflection down to 5.35% in the spectrum range of 400-1000nm wavelength was achieved, which is 7.8% lower than inverted pyramid without additional nitride coatings. To quantitatively evaluate the light trapping performance of the textures, the enhancement factor in the dome case is 45%, while for the pyramid texture the AE factors is only around 39.7%. In addition, the absorbed photocurrent density is 14.38 mA/cm2 for a 2 μm silicon absorber layer at an incidence angle of 0°, which is 1.32 mA/ cm2 higher than inverted pyramids. The proposed structure has the potential to play a key role in thin film solar cells.
KEYWORDS: Silicon, Nanostructures, Absorption, Reflectivity, Solar cells, Silicon films, Thin film solar cells, Silicon solar cells, Diffraction gratings, Nanolithography
Enhancing the light absorption in ultrathin-film silicon solar cells is important for improving efficiency and reducing cost. In this paper, we report a highly effecient cosine periodic nanostructure as light trapping texture. The design and fabrication as well as measurement of cosine nanotextures were presented. The optimized structure yields an average reflectance of 7.07% at an equivalent silicon thickness of 10μm, much better than planar and random pyramid structures. The measurements demonstrate that the absorptions in ultrathin film solar cells are very close to the Yablonovitch limit for the entire solar spectrum and insensitive to the angle of the light. This approach is applicable to various thicknesses and promising in future glass-based thin film solar cells.
An optical fiber hydrogen sensor based on the measuring principle of surface plasma resonance is introduced. The
structure of the hydrogen-sensitive head which is coated with Pd-Ag alloy film on the surface of the etched optical fiber
is investigated theoretically. When hydrogen gas is absorbed into the Pd thin layer of the sensing head, the Pd hydride is
formed and then the refraction index of the etched optical fiber surface will be changed with different hydrogen gas
concentration. The surface plasma wave is stimulated by the light wave in optical fiber and the surface plasma resonance
occurs between the thin metal layer and the medium surface of hydrogen gas. The Pd-Ag alloy film thickness versus the
sensitivity of hydrogen sensing head is analyzed and optimized via the numerical method. The sensing head which is
based on surface plasma resonance is manufactured and used in the experiment system of hydrogen gas detecting, and
the experiment results demonstrate that the detecting system has high sensitivity with the hydrogen concentration in the
range of 0%-4%, the accuracy, resolution and response time are respectively 5%, 0.1% and 30s. This sensor structure can
be applied to detecting the low concentration of hydrogen gas.
The continuing size reduction of integrated circuits to nano dimensions requires the development of advanced
lithographic techniques. In order to obtain the desired feature sizes, it has become increasingly complex and high-cost to
use the established methods of optical projection lithography at short optical wavelengths. Surface-plasmon polariton
interference lithography (SPPIL) can provide a feasible way to achieve or approach the ultimate resolution for a certain
wavelength without requiring complicated and expensive large numerical aperture optics. But it demands the fabrication
of gratings with very fine period as a mask to realize contact printing, and the imaging quality is seriously dependent on
the structure and materials of the mask, the illuminating light, photoresist, etc. So the optimization of the technological
parameters is important to improve the imaging quality of nanolithography based on surface-plasmon polariton(SPP). In
this paper, the simulation of near-field distribution of SPPIL is performed using Finite Difference Time Domain FDTD
method, and the impacts of some technological conditions to the exposure field are analyzed including the polarization
state and wavelength of the illuminating light, the periodicity, thickness and slit width of the mask, and so on. The
simulation results show that, it is possible to fabricate good quality pattern with about 60nm features, with SPPIL using a
436nm-wavelength incident light.
A novel method for the fabrication of continuous micro-optical components is presented in this paper. It employs a computer controlled digital-micromirror-device(DMDTM) as a switchable projection mask and silver-halide sensitized gelatin (SHSG) as recording material. By etching SHSG with enzyme solution, the micro-optical components with relief modulation can be generated through special processing procedures. The principles of etching SHSG with enzyme and theoretical analysis for deep etching are also discussed in detail, and the detailed quantitative experiments on the processing procedures are conducted to determine optimum technique parameters. A good linear relationship within a depth range of 4μm was experimentally obtained between exposure dose and relief depth. At last, the microlensarray with 256.8μm radius and 2.572μm depth was achieved. This method is simple, cheap and the aberration in processing procedures can be corrected in the step of designing mask, so it is a practical method to fabricate good continuous profile for low-volume production.
A red-sensitive acrylamide-based photopolymer based on multiple polymerizable monomers is developed in this paper for holographic applications. In order to improve the spatial resolution of this photopolymer system, a new strategy of employing low molecular-weight polyvinyl alcohol as binder is proposed. The comparative experiments of different photosensitive system with various molecular weights (72000,15000, 9000) are conducted to study their effects on the diffraction efficiency and spatial resolution. The experimental results show that the photosensitive system with low molecular weight of 9000 has much higher resolution and diffraction efficiency, and bright volume transmission grating with spatial frequency of 3000 lines/mm and diffraction efficiency higher than 85% can be recorded successfully on the optimum photopolymer material at the exposure level of 40 mJ/cm2. Some preliminary applications of spatial and angular multiplexing holographic storage for storing multiple binary and grey-tone optical images, are successfully demonstrated.
A novel method for the fabrication of continuous micro-optical components is presented in this paper. It employs a computer controlled spatial-light-modulator (SLM) as a switchable projection mask and silver-halide sensitized gelatin (SHSG) as recording material. By etching SHSG with enzyme solution, the micro-optical components with relief modulation can be generated through special processing procedures. The principles of digital SLM-based lithography and enzyme etching SHSG are discussed in detail, and microlens arrays, micro axicon-lens arrays and gratings with good profile were achieved. This method is simple, cheap and the aberration in processing procedures can be in-situ corrected in the step of designing mask, so it is a practical method to fabricate continuous profile for low-volume production.
In this paper, a red-sensitive photopolymer based on multiple polymerizable monomers is developed for holographic applications. The detailed quantitative experiments on the reagent concentrations, the exposure, the thickness of the photosensitive layer, are conducted to determine an optimum recipe, and bright volume phase holograms with high diffraction efficiency are obtained in our experiments at the exposure level of 4mJ/cm2. This photopolymer also has higher resolution and self-development capacity. This makes it very convenient and useful for the applications of both real-time and double exposure holographic interferometry, some preliminary experiments of holographic interferometry are demonstrated in this paper for the nondestructive testing and measurement of minor distortion and displacement.
A maskless lithography imaging simulation using digital micromirror device (DMD) was investigated. The DMD acts as a reflective spatial light modulator. The micro-mirrors on DMD can be instructed by the computer to tilt them ±12° off their normal position which produces a mask pattern, and then the mask pattern can be carried onto the surface of wafer by the imaging system. Because the imaging of the maskless lithography is a complex process, it is necessary to simulate and analyze its practical process. In this paper, we present a partial coherent imaging model of maskless lithography considering the practical projection characterization of DMD. With the model, it is convenient to simulate the lithography of arbitrarily shaped microstructure using DMD. Through calculation, the spatial image in maskless lithography process based on gray scale photolithography with DMD real-time masks was obtained.
In this paper, a new technique is presented for adjusting the playback wavelength of Lippmann holograms recorded in methylene-blue sensitized dichromated gelatin (MBDCG). The main feature of this technique is introducing a water-soluble organic reagent into MBDCG photosensitive layer as preswelling reagent and wavelength adjuster. This method has wide wavelength adjustment range and high signal-to-noise ratio, can be applied to adjust the playback wavelength of reflection hologram quantitatively by changing the concentration of preswelling reagent. Its possible applications include color image display, holographic optical elements, and optical anti-counterfeiting.
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