Technological process for a new silicon solar cell structure with honeycomb textured front surface

This paper presents a new silicon solar-cell structure improved by texturisation of the front surface using silicon micromachining technologies. A ‘honeycomb’-textured front surface has been obtained through a photolithographical process to generate patterns (disc holes) on the front surface followed by isotropic etching (in HNO₃: HF: CH₃COOH) until the wells joined together.For front-surface loss characterisation, the spectral dependence of the front-surface reflectivity has been investigated by spectrophotometrical measurements. The surface reflectivity was lowered under 10% and this value was a good one compared to the reflectivity of silicon monocrystalline wafer untextured surface. The p–n junction made by phosphorous diffusion at 0.8 μm follows the honeycomb profile. In order to obtain low series resistance, a p+ boron diffusion on the back of the structure was made. The fabrication process was completed with an ohmic contact (Al on top and on the back surface).     

Texturisation of multicrystalline silicon solar cells by RIE and plasma etching

Texturing by reactive ion etching (RIE) is demonstrated as an attractive technical solution for lowering of reflectance of multicrystalline silicon solar cells. A suitable sequence of processes is developed to combine the advantage of reactive ion etching with “natural lithography” based on colloidal masks. The RIE single-wafer texturisation is driven to an industrial applicable batch process by plasma etching with a gain in efficiency of 0.3% absolute.     

Texturisation of multicrystalline silicon wafers for solar cells by reactive ion etching through colloidal masks

Texturing of multicrystalline silicon solar cells by reactive ion etching (RIE) is demonstrated as an attractive solution for lowering of reflectance. A suitable sequence of processes is developed to exploit the advantage of RIE in combination with “natural lithography” based on colloidal masks. A homogeneous particle coverage on 4 in. monocrystalline wafers and on 100×100 mm² multicrystalline wafers (Baysix) has been achieved. Finally, texture is obtained by RIE patterning. Data of optical properties are presented. A significant lowering of the reflection of textured wafers compared to untexture is achieved for all states of solar cell production.     

菜籽油超声波法制备生物柴油的研究

以菜籽油和甲醇为反应原料,以KNO3/Al2O3为催化剂,采用超声波法制备生物柴油,考察了超声波频率、醇油物质的量比、催化剂用量等条件对反应的影响。试验结果表明,该反应的最佳条件:超声波频率为30kHz,醇油物质的量比为7∶1,催化剂用量为菜籽油质量的2.0%。在此条件下,生物柴油产率为94%。所得生物柴油的主要性能指标均符合德国的生物柴油标准。     

Microscopic homogeneity of emitters formed on textured silicon using in-line diffusion and phosphoric acid as the dopant source

An important point of comparison between POCl₃ emitter diffusion in a quartz tube furnace and in-line diffusion using sprayed phosphoric acid is the microscopic homogeneity of the diffusion, i.e. the homogeneity along the texture of a silicon surface. Two characterization methods were used. In each case, the cross-section of cleaved mc-Si and Cz-Si textured samples was observed in a scanning electron microscope (SEM). First, the thickness of the phosphosilicate glass (PSG) was measured. Second, the emitter was observed on SEM images which showed the n-type silicon as a darker region. The results show comparable homogeneity for in-line and POCl₃ diffusion.     

Effect of ultrasonic frequency on electrochemical Si etching in porous Si layer transfer process for thin film solar cell fabrication

A porous Si (PS) layer transfer process that monocrystalline Si film grown on a Si substrate wafer is separated with the substrate and transferred to a non-Si device realizes to get monocrystalline Si film on low-cost substrates such as glass. PS film is fabricated by electrochemical etching in a chemical mixture of HF and ethanol. Effect of ultrasonic frequency on surface morphology of PS film is studied. By applying ultrasonic waves during etching, the pores on PS film with uniform size can be fabricated.     

超声波制备生物柴油技术的研究进展

超声波技术作为一门新兴的技术已受到普遍关注.文章综述了近年来国内外超声波技术在生物柴油制备中应用的研究现状、制备原理和优缺点,指出了该技术在生物柴油制备中须要解决的问题,在此基础上提出超声波制备生物柴油技术的发展方向,认为开发更优良的的制备工艺是今后超声波制备生物柴油技术研究领域的主要任务.     

Generating and focusing of underwater expansion wave using a silicon resin reflector

In the present study, an ellipsoid reflector was designed and produced using silicon resin in order to generate and focus expansion wave in water for the purpose of a medical application. Across an expansion wave the static pressure, temperature and density decrease, as a result, negative pressure is given behind the expansion wave generated in the water, and then a tensile stress is induced. As an acoustic impedance of the silicon resin is almost similar to that of water, the interface of air-silicon resin would be regarded as the same with that of the air-water. A high voltage discharge was used as an energy source of underwater shock wave. When the underwater shock wave reflects on this interface, it is already clear that the shock wave converts to the expansion wave. The generation and focusing of the expansion wave were carried out and the phenomena were observed by flow visualization using a high-speed camera.     

应用超声波技术处理污泥的现状分析

污水处理过程中产生大量的污泥,这些污泥的含水量高,并含有大量的微生物和病原体,需要进行有效的处理处置。简述了超声波作用于污泥的机理:通过超声空化作用产生的强有力水流喷射的剪切力对污泥发生作用;总结了超声波在污泥处理中的应用情况。重点阐述了超声波能促进污泥脱水,即超声能产生一种海绵效应使水分子更易在波面的通道传播,超声破坏菌胶团使内部水释放出来;超声波能促进污泥消化,缩短污泥发酵时间并能提高沼气的产率以及超声波能破解污泥等的研究状况。     

High quality textured ZnO:Al surfaces obtained by a two-step wet-chemical etching method for applications in thin film silicon solar cells

ZnO:Al films deposited at 250 °C on Corning glass by radio frequency magnetron sputtering were studied for their use as front contact for thin film silicon solar cells. For this purpose, a two-step etching method combining different concentrations of diluted hydrochloric acid (from 0.1% to 3%) with different etching times was developed. Its influence on morphological, electrical and optical properties of the etched films was evaluated. This new etching method led to more uniform textured surfaces, where the electrical properties remained unchangeable after the etching process, and with adapted light scattering properties similar to those exhibited by commercial substrates.     

Characteristics of the oblique detonation flow field induced by a complex wave structure

In this paper, the initiation characteristics of the oblique detonation flow field induced by single- and double-wedge surfaces of finite length in a confined space are investigated. Numerical simulations with a detailed H₂/air reaction and theoretical shock polar analyses are combined to study the influence mechanism of a complex wave system structure on the characteristics of the oblique detonation. The effects of expansion waves on the oblique detonation waves (ODWs) and their flow field characteristics for different equivalent ratios and geometric sizes are analyzed in single-wedge and double-wedge structures with the same inflow parameters. The results show that the length of the induced ODW is shorter in the double-wedge structure than in the single-wedge structure. For the single-wedge structure, the strength of the expansion wave increases, the wall temperature drops, and the characteristic length of the induction zone decreases with increasing deflection angle of the second wedge. If the strength of the expansion wave is sufficiently large, the ODW is initiated. For the double-wedge structure, the ODWs interact and form a complex wave system structure, consisting of a Mach stem, two reflected detonation waves and slip lines. The length and the temperature before and after the Mach stem decrease with an increase in the strength of the expansion waves. The effects of the expansion waves on the flow field of the ODW are relatively small at a large equivalent ratio and significantly larger at a small equivalent ratio.     

Antireflection subwavelength structure of silicon surface formed by wet process using catalysis of single nano-sized gold particle

Subwavelength structure (SWS) was formed by simple wet chemical etching using catalysis of gold (Au) nanoparticle. Single nano-sized Au particle dispersion solution was coated onto silicon (Si)(1 1 1) substrate with polished surface. Then, the samples were soaked in an aqueous etching solution of hydrofluoric acid and hydrogen peroxide. The surface of 15-min-etched Si substrate appeared black. The reflectivity of the Si substrate was reduced to below 5% throughout the entire spectrum from 300 to 800 nm owing to SWS. The fractional area occupied by Si as a function of the depth across the textured layer showed a smooth increase of density up to a depth. The observed optical effects were explained by the formation of a subwavelength scale taper structure, representing an effective medium with a smooth transition of the refractive index from air to Si.     

Theoretical investigation on the absorption enhancement of the crystalline silicon solar cells by pyramid texture coated with SiNx:H layer

The absorption enhancement of the crystalline silicon (c-Si) solar cells by pyramid texture coated with SiN_x:H layer was investigated by theoretical simulation via rigorous coupled-wave analysis (RCWA). It was found that in order to maximize the spectrally weighted absorptance of the solar cells for the Air Mass 1.5 (AM1.5) solar spectrum (A_AM1.5), the required pyramid size (d) was dependent on the thickness of the c-Si substrate. The thinner the c-Si substrate is, the larger the pyramids should be. Pyramids with d > 0.5 μm can make A_AM1.5 maximal if the c-Si substrate thickness is larger than 50 μm. But d > 1.0 μm is needed when the c-Si substrate thickness is less than 25 μm. If the c-Si substrate is thinner than 5 μm, even d > 4.0 μm is required. The underlying mechanism was analyzed according to the diffraction theory. The pyramid texture acts as not only an antireflective (AR) component, but also a light trapping element. Then, the optimized refractive index and the thickness of SiN_x:H layer to further enhance the absorption were given out. The potential solar cell efficiency was also estimated.     

Propagation process of H2/air rotating detonation wave and influence factors in plane-radial structure

The rotating detonation wave (RDW) propagation processes and influence factors are simulated in the plane-radial structure. The effects of inner radii of curvature, domain widths and stagnation pressures on propagation mode are studied. The RDW is initiated, and two kinds of propagation mode are obtained and analyzed. The flow field structure, parameters variation and influence factors on unstable propagation mode are explored in depth, and the geometrical and injection conditions of the unstable propagation are obtained. Results indicate that the decoupling and re-initiation occur repeatedly during the unstable propagation mode of the RDW, and the angular velocities of leading shock wave vary accordingly. When the domain width remains constant, the range of stagnation-pressure under unstable propagation mode increases as the inner radius increases. But the RDW propagates steadily when the inner radius increases to a certain value (Larger than 40 mm in this study). The effect of curvature radius and initial pressure ahead of detonation wave on the unstable propagation mode in this calculation model is similar to that in a curved channel. When r_i +0.464p_a > 80.932 or r_i ≥ 40 mm, the detonation wave can propagate steadily in the annular domain. When the curvature radius remains constant, the stagnation-pressure range of the unstable propagation mode decreases as the domain width increases.     

Improvement on surface texturing of single crystalline silicon for solar cells by saw-damage etching using an acidic solution

Texturing the surfaces of silicon wafer is one of the most important ways of increasing their efficiencies. The texturing process reduces the surface reflection loss through photon trapping, thereby increasing the short circuit current of the solar cell. The texturing of crystalline silicon was carried out using alkaline solutions. Such solutions resulted in anisotropic etching that leads to the formation of random pyramids. Before the texturing process was carried out, saw-damage etching was performed in order to remove the surface defects and damage caused by wire sawing. In general, potassium hydroxide (KOH) solution has been used for saw-damage etching. This etching results in a fairly flat surface. The results from this study showed that the outcome of the surface texturing is related to the original surface morphology of the silicon. It was found that saw-damage etching using an acidic solution improved the effects of the texturing. In this case, regular and small pyramids were formed on the surface of the silicon. This reduced the reflectance of the surface, thereby increased the short circuit current and the conversion efficiency of the solar cell.     

Bundle-type silicon nanorod anodes produced by electroless etching using silver ions and their electrochemical characteristics in lithium ion cells

This study investigates bundle-type silicon nanorods (BSNR) that are aimed at improving the discharge capacity and life cycle characteristics of secondary cells, by controlling the shape and etching depth of silicon thick-films produced by electroless etching. The prepared BSNR structure is composed of a columnar bundle, having a diameter of 100 nm and lengths of 1.5 and 3.5 μm. The etching depths of the nanorods have a significant effect on the electrochemical performance characteristics, including the capacity fading and coulombic efficiency. Using a BSNR electrode therefore allows for an anode with a high capacity and efficiency in lithium ion cells, and can help overcome the issues associated with conventional silicon thick-films. Furthermore, as a result of its unique self-relaxant structure, electrode deterioration is improved through mitigation of the volume change.     

翼型表面随行波结构流动控制的数值研究

针对翼型表面的流动分离,采用数值模拟方法研究随行波结构流动控制的机制。为了验证计算方法的可靠性,将翼型表面静压曲线与实验测试结果进行对比,发现两者吻合程度较好。数值计算结果表明,适当增加随行波的相对弦长长度,有助于改善翼型的气动性能。当攻角小于3°时,随行波位于分离点之前,沟槽内形成顺时针旋转的二次涡,有助于加速边界层低速条带;在大攻角下,随行波位于分离点之后,顺时针卷起的分离涡在沟槽内形成逆时针旋转的二次涡,与分离涡互为反向涡对,减小了尾缘分离区范围。翼型表面随行波能有效地控制边界层流动。     

Efficiency potential of thin film polycrystalline silicon solar cells by silane-gas-free process using aluminum-induced-crystallization

Analyzing the performance of thin film polycrystalline silicon solar cells fabricated by silane-gas-free process including the aluminum-induced-crystallization technique by using the device simulation program “PC1D”, we have estimated the efficiency of them. In addition, we have discussed the issues to make the silane-gas-free process practical. In the cell fabrication by silane-gas-free process, segregation of impurity atoms at the grain boundaries of the Si film is one of the serious problems. By suppressing the impurity inclusion and optimizing the cell parameters, the simulated efficiency is to be about 13% in single-junction cells.     

Effects of fluorine doping on the structural properties of the CdO films deposited by ultrasonic spray pyrolysis

The fluorine doped cadmium oxide samples have been deposited at 250 °C by ultrasonic spray pyrolysis method. X-ray diffraction patterns of the CdO:F samples have revealed that the samples are polycrystalline with cubic sodium chloride structure. The texture coefficients calculated for various planes at different fluorine concentrations indicate that the samples have exhibited (1 1 1) and (2 0 0) preferential orientations. The lattice parameters for cubic structure of each diffraction plane have been calculated. The crystallite size of the samples being nearly constant until 4% of fluorine doping showed reasonable decrease above this concentration value. The macro strain and dislocation density vary with fluorine concentrations.