Deposition of microcrystalline silicon by electron beam excited plasma

Hydrogenated microcrystalline silicon (μc-Si:H) films were deposited by electron beam excited plasma (EBEP) CVD. As the SiH₄ flow rate increases, deposition rate steeply increases, however, crystalline fraction and grain size decrease. A high deposition rate of 69 nm/min is achieved using SiH₄ without H₂ dilution. It is shown that H atom plays key roll for μc-Si:H formation. Results show that deposition mechanism of μc-Si:H by EBEP is mainly controlled by the reaction in the plasma rather than the reaction on the film surface.     

Hydrogen passivation of defects in polycrystalline silicon solar cells

The investigations of hydrogen passivation of defects in polycrystalline silicon produced by the Czochralski method have been carried on. The results presented give evidence that it is advisable to use this material to create cheap effective solar cells.     

Research on new method of electron beam candle melting used for removal of P from molten Si

Abstract

A new method, electron beam candle melting (EBCM), is proposed for the removal of P in molten Si, to produce high quality material such as solar grade silicon for photovoltaic applications. EBCM is designed to overcome the shortcomings of electron beam melting while utilising the high saturated pressure of P in molten Si to effect refining. The experimental result showed that it could remove P from Si effectively; in addition, the energy utilisation ratio was experimentally proved to be high. The evaporation coefficient of P removal is in a reasonable region and comparable with the theoretical value, which indicates that EBCM is a feasible method for the removal of P in molten Si in low power.     

Structural properties of phosphorous-doped polycrystalline silicon

The structural properties and hydrogen bonding of undoped and phosphorous doped polycrystalline silicon produced by step-by-step laser dehydrogenation and crystallization technique were investigated using Raman spectroscopy and hydrogen effusion measurements. At low laser fluences, E_L, a two-layer system is created. This is accompanied by the change in hydrogen bonding. The intensity of the Si–H vibration mode at 2000 decreases faster than the one at 2100 cm⁻¹. This is even more pronounced in phosphorous-doped specimens. The laser crystallization results in an increase of the hydrogen binding energy by approximately 0.2–0.3 eV compared to the amorphous starting materials.     

Passivation and etching of fine-grained polycrystalline silicon films by hydrogen treatment

Here we investigated the effects of hydrogen treatment on highly defected polycrystalline silicon solar cells in terms of defects passivation and surface etching. The poly-Si films were formed by high-temperature chemical vapour deposition. The hydrogen treatment was carried out through deposition of a-SiN_x:H layer followed by a thermal treatment or by direct hydrogen plasma. The deposition of silicon nitride layers on polysilicon cells led to a slight increase in the open-circuit voltage without damage to the surface. In contrast, after plasma hydrogenation, the results revealed an etching process of the emitter simultaneously with an important increase of the measured open-circuit voltage by a factor 2, reaching 420 mV.     

EELS microanalysis of polycrystalline silicon thin films for solar cells grown at low temperatures

The aim of this work is the quantitative chemical analysis of polycrystalline silicon thin films grown on glass substrates at temperatures <600°C by means of transmission electron microscopy (TEM) and electron energy-loss spectrometry (EELS). Specimens produced with two different methods were investigated. We found significant differences in grain size and morphology, as well as in the distribution of oxygen. A surprisingly high amount of Ba diffusion from the subtrate was detected.     

Development of low cost production technologies for polycrystalline silicon solar cells

To develop a technology of forming grooves for low cost cell production, a multi-blade wheel grinding method was investigated. The process time of groove formation on the surface of 10 × 10 cm² polycrystalline silicon substrate was reduced to 30 s by a newly developed high-speed groove formation machine. Simultaneous formation of junction and anti-reflection coating by atmospheric pressure chemical vapor deposition (APCVD) technique was also investigated. For electrodes formation process, single firing method for both side electrodes made possible to simplify the firing process and to speed up from a conventional speed of 400 mm/min to 5000 mm/min.     

A study of electrical uniformity for monolithic polycrystalline silicon solar cells

The aim of this work is to investigate the electrical uniformity of monolithic polycrystalline silicon solar cells prepared by various process techniques. By a series of experiments such as P and Al impurity gettering and silicon nitride passivation, a new conclusion is that the application of P and Al gettering as well as silicon nitride passivation enhances the electrical uniformity of small area solar cells diced from the same polycrystalline silicon solar cells, even if impurity gettering is not effective when the dislocation density is above a threshold value of about 10⁶ cm⁻². The experiments give us some hints that when we cut large area polycrystalline silicon solar cells into small pieces needed for application, we should modify production process slightly.     

Hydrogen effect on Ti-6.5Al-3.5Mo-1.5Zr-0.3Si parts produced by electron beam melting

In this work, the hydrogen sorption kinetics as well as the hydrogen effect on phase transformations, structure and properties of additively manufactured Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy using electron beam melting (EBM) were studied. In situ X-ray diffraction complex was used to analyze phase transitions in the EBM Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy under hydrogenation in gas atmosphere. The EBM mode is found to affect significantly on the microstructure and the rate of hydrogen sorption by Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy during hydrogenation at a temperature of 650 °C. The measurements have shown that the highest rate of hydrogen absorption is observed in samples manufactured at the beam current of 3 mA and the scanning speed of 150 mm/s. Hydrogenation of the samples leads to redistribution of alloying elements in the titanium alloy resulted in the formation of aluminum-rich α₂-Ti₃Al intermetallic phase and hydrides precipitation.     

Metal impurities behaviors of silicon in the fractional melting process

The photovoltaic (PV) rapid growth suffers the severe shortage of silicon. The metallurgical route to solar grade (SoG) silicon is the alternative solution. One of the methods suggested the fractional melting process. Because the metal impurities in the metallurgical grade (MG) silicon such as Fe, Al, Ti and Cu deteriorate the efficiency of the solar cell seriously, it is important to remove those metal elements from MG-Si to upgrade the silicon. The refining behaviors of the metal impurities, however, do not equal in FM process. Cu and Al behaviors in the Si during FM process are studied using SEM, EPMA and ICP-AES. The diffusion coefficient and the grain boundary (GB) enrichment behaviors of the elements are rationalized to cause the difference.     

Laser-beam-induced current mapping evaluation of porous silicon-based passivation in polycrystalline silicon solar cells

In the present work, we report on the effect of introducing a superficial porous silicon (PS) layer on the performance of polycrystalline silicon (pc-Si) solar cells. Laser-beam-induced current (LBIC) mapping shows that the PS treatment on the emitter of pc-Si solar cells improves their quantum response and reduce the grain boundaries (GBs) activity. After the porous silicon treatment, mapping investigation shows an enhancement of the LBIC and the internal quantum efficiency (IQE), due to an improvement of the minority carrier diffusion length and the passivation of recombination centers at the GBs as compared to the reference substrate. It was quantitatively shown that porous silicon treatment can passivate both the grains and GBs.     

Low-temperature deposition of polycrystalline silicon thin films by hot-wire CVD

Polycrystalline silicon films have been prepared by hot-wire chemical vapor deposition (HWCVD) at a relatively low substrate temperature of 430°C. The material properties have been optimized for photovoltaic applications by varying the hydrogen dilution of the silane feedstock gas, the gas pressure and the wire temperature. The optimized material has 95% crystalline volume fraction and an average grain size of 70 nm. The grains have a preferential orientation along the (2 2 0) direction. The optical band gap calculated from optical absorption by photothermal deflection spectroscopy (PDS) showed a value of 1.1 eV, equal to crystalline silicon. An activation energy of 0.54 eV for the electrical transport confirmed the intrinsic nature of the films. The material has a low dangling bond-defect density of 10¹⁷ cm³. A photo conductivity of 1.9 × 10⁻⁵ Ω⁻¹cm⁻¹ and a photoresponse (σ_ph/σ_d) of 1.4 × 10² were achieved. A high minority-carrier diffusion length of 334 nm as measured by the steady-state photocarrier grating technique (SSPG) and a large majority-carrier mobility-lifetime (μτ) product of 7.1 × 10⁻⁷cm²V⁻¹ from steady-state photoconductivity measurement ensure that the poly-Si : H films possess device quality. A single junction n---i---p cell made in the configuration n⁺-c-Si/i-poly-Si: H/p-μc-Si : H/ITO yielded 3.15% efficiency under 100 mW/cm² AM 1.5 illumination.     

Distinguishing morphological and electrical defects in polycrystalline silicon solar cells using scanning electron acoustic microscopy and electron beam induced current

Morphological and electrical defects in polycrystalline silicon solar cells are distinguished by scanning electron acoustic microscopy (SEAM) and electron beam induced current (EBIC) techniques, respectively. It was found that while some defects are both morphologically and electrically detectable, some are predominantly only either electrical or morphological in nature. Combining both SEAM and EBIC is therefore an ideal approach as the two techniques can provide complementary information on both the morphological and electrical manifestation of the defects.     

Dislocation-related deep levels in carbon rich p-type polycrystalline silicon

We present a study of dislocation-related defects in boron-doped p-type silicon crystals grown by the edge-defined film-fed growth (EFG) and float-zone (FZ) method. Deep level transient spectroscopy (DLTS) was used to identify electrically active defects. We have observed a E_v+0.33 eV level in EFG silicon and a E_v+0.39 eV in FZ silicon. In order to measure defect capture cross sections, we examined the intensity of the DLTS signal and peak position as a function of filling-pulse duration. The traps, both in EFG and FZ silicon, exhibit a logarithmic capture kinetics, a feature typical for extended defects such as dislocations. However, the complex behavior of defects in EFG material suggests that either the dislocations are decorated with clouds of carbon related or metallic defects, or its close spacing produces overlap of space charge regions, affecting therefore, its electrical activity.     

肝癌碘油栓塞后肝区平片所见碘油沉积量与疗效关系

本文分析了90例肝癌肝动脉灌注化疗碘油栓塞后,肝区平片所见碘油沉积量和疗效的关系。碘油沉积分为多,中,少三组,从ATP下降,肿瘤缩小率及一年生存率三方面比较。结果沉积多的与中等组三项都有显著差别;沉积中等的与少的组差别不明显。说明碘油沉积要达到一定的量后,疗效才会显著提高。同时分析了影响碘油沉积的几个因素。     

夏宝枢教授

炉底上涨是三相交流矿热炉冶炼硅钙合金的最大难题，造成炉底上涨的主要原因是炉底温度低。本文作者在研究目前各种冶炼工艺之后，设计出一台容量４００ｋＷ直流硅钙炉，并进行了冶炼硅钙合金试验，得到超出预料的可喜成果。     

Modelling of material properties influence on back junction thin polycrystalline silicon solar cells

The influence of polycrystalline silicon properties on the performances of thin back junction solar cells has been investigated by means of a 3-dimensional model taking into account grain size, grain boundary recombination, volumic recombination, and surface recombination. The drastic influence of front surface recombination has been confirmed. The grain size has been shown to be of minor importance provided the grain size is not too small and the grain boundaries are correctly passivated. An optimal base thickness has been determined which is all the smaller that the material is more imperfect.     

Effects of grain boundaries in polycrystalline silicon thin-film solar cells based on the two-dimensional model

The two-dimensional calculation for polycrystalline Si thin-film solar cells was performed. Two models, “stripe structure” and “columnar structure”, were applied for the solar cells composed of grains. For the stripe structure of 20 μm active layer, to keep the efficiency distribution within 5% for individual unit cells, the stripe width requires more than 500 μm for a minority-carrier lifetime of 1×10⁻⁵ s and recombination velocity at the grain boundary of 1×10⁴ cm/s. For the columnar structure of 10 μm active layer, to keep the efficiency independent of grain size, the recombination velocity should be kept less than 1×10³ cm/s. If imperfect passivation of a grain boundary is given, the way of decreasing carrier concentration to 10¹⁴ cm⁻³ in an active layer may realize insusceptible output. An appropriate device modeling is needed in the two-dimensional calculation for polycrystalline Si thin films with an electron diffusion length close to or more than grain size and with a poorly passivated grain boundary. The calculated efficiency using bad model will include an error of about 1% as overestimation.     

中频无芯感应熔炼炉熔炼过程中断后的温度特性数值模拟

对中频无芯感应熔炼炉内钢料在熔化过程中断后的降温和凝固过程进行了数值模拟。研究了熔化过程中突然断电后熔炼炉内钢料的相界面变化、温度分布及变化的规律。讨论了正常熔化时间即断电前炉内状态对断电后钢液凝固和炉内温度变化的影响。结果表明：正常熔化中突然断电后,熔化仍将进行,但相界面移动速度变小,熔化逐渐终止;正常熔化时间越长后,断电后继续熔化的钢量越多。     

圆形铝熔炼炉内非稳态热工过程数值模拟

针对铝熔铸过程中常用的圆形铝熔炼炉,利用FLUENT软件,根据能量守恒方程、动量方程建立铝熔炼炉内热工过程数学模型,采用标准k-ε湍流模型、P-1辐射模型对铝熔炼炉内非稳态传热及流动过程进行数值模拟研究。考虑到铝料熔化过程会消耗一部分能量,采用等效比热法将铝料的熔化潜热转换为相应的比热值进行计算。通过数值模拟得到了炉内流场、炉膛及铝料温度场分布情况。模拟结果与实际情况相符,为铝熔炼炉的设计与优化研究提供了理论依据。