太阳电池硅片ELCC技术用复合梯度涂层的研究

低成本太阳电池硅片电磁悬浮熔炼离心铸造（ＥＬＣＣ）技术可大幅度降低太阳电池的成本。硅片脱模技术是ＥＬＣＣ技术的关键之一。综合运行液相反应生成法，反应烧结法和溶胶－凝胶法，成功地在石墨基体表面制备了ＳｉＣ－Ｓｉ３Ｎ４－（Ｓｉ３Ｎ４＋ＳｉＯ２）复合梯度涂层，并用Ｘ射线衍射法（ＸＲＤ）、扫描电镜（ＳＥＭ）和界面性能测定仪（ＩＣＭ）考察了该涂层的组织结构和性能。     

电磁悬浮熔炼离心铸造设备的研制

电磁悬浮熔炼离心铸造（ＥＬＣＣ）技术是大幅度降低太阳电池硅片成本的一条新途径。报道了该设备的研制及总体设计方案，介绍了炉体、电源系统、机械系统、辅助系统及其相互配合。该设备已应用于ＥＬＣＣ技术及其相关工艺的研究。     

太阳电池硅片ELCC技术模具温场的计算机模拟

运用有限元法对太阳电池片电磁悬浮炼离心铸造技术中成形模具的稳态温度场进行了计算机模。模拟结果表明：当炉堂温度为１４５０℃时，在模具型腔内，中心浇口处温度最高，达到１３９０℃，边缘处温度较低，也有１３５０℃，接近硅的熔点温度；在所关心的模具型腔尺寸范围内，径向温度梯度大于３．５℃／ｍｍ，且中心浇口温度高于边缘温度，这种温度梯度分布特征有利于硅片凝固应力的及时释放，避免硅片的破裂；轴向温度梯试大于８℃     

浅析银铜双金属一步法制备的黑硅多晶硅太阳电池的性能

为了研究银铜双金属一步法黑硅技术,对采用该方法处理后的黑硅多晶硅硅片进行测试,并以产线工艺为基础制备黑硅多晶硅太阳电池;使用测试仪等研究了黑硅多晶硅硅片的显微组织、界面结构、宏观形貌,以及黑硅多晶硅太阳电池的量子响应、电性能参数与光衰性能。结果表明,黑硅多晶硅太阳电池的电性能有显著提升,尤其是短路电流提升了221 mA,这主要是由于黑硅多晶硅太阳电池的短波段量子响应有显著改善;同时,黑硅多晶硅太阳电池的光衰特性优于常规多晶硅太阳电池。     

多晶硅真空定向凝固系统的结构特性优化研究

采用非稳态集中参数法分别计算了沿轴向和径向增加装料量对多晶硅定向凝固过程中加热时间的影响,并通过数值模拟对比分析了多晶硅定向凝固过程中晶体生长时的温度场、熔体流动、固-液界面形状和应力大小及分布等情况。并对装料沿径向增加以提高单炉生产率的方案提出了添加硅料表面上加热器的优化措施,不仅可以显著缩短加热时间,还能减小硅料的径向温度梯度,调节固-液界面形状。这将为大型化多晶硅真空定向凝固设备的优化设计与开发利用提供理论基础。     

光伏制造业:现状、前景及研究需求(二)

(2)非切割硅片 目前,线切割技术的进步已使硅片厚度降低到180μm,但仍有超过50％的硅料浪费在锯屑或切口中.这些硅碎末虽可重复利用,但人们希望能彻底取消线切割工艺.无切割硅片能明显降低硅用量(目前工业平均水平为3～6g/W).20世纪70年代,研究者已经研发出从熔融硅中直接制备硅片的技术,经过几十年的发展,这类技术目前已推向市场,主要包括边缘薄膜生长(EFG)技术及硅带技术.EFG技术采用毛细管原理,硅片直接通过石墨细管从熔融硅中提拉.     

太阳能级硅的电磁悬浮熔炼

电磁悬浮与离心铸造技术(ELCC)开辟了低成本制备太阳电池用硅片材料的新途径。硅材料的无污染熔炼是进行ELCC硅片成形的重要前提。采用电阻与高频感应相结合的两级加热方法，成功地实现了太阳能级硅的电磁悬浮熔炼，为低成本太阳电池的研制奠定了基础。实验还发现，与传统的理论计算不同，悬浮力随电源频率的不断下降而提高。     

一种燃机叶片试板定向凝固过程的研究

明确铸件定向凝固过程中的温度变化规律．可以避免重型燃气轮机定向叶片铸造中出现的一些缺陷。文章选取了与某重型燃机第1级涡轮动叶尺寸相近的试板．采用定向凝固高温合金DZ445．研究了该试板在实际工业生产用定向结晶炉中的定向凝固过程,结果表明：在距离水冷铜盘位置〉50mm后固液界面形态将发生大的转变,温度梯度逐渐变小,〉100mm后温度梯度基本保持不变．这为后续制定叶片抽拉工艺给出了参考。该实验还通过热电偶获得的定向凝固过程中温度一时间曲线与ProCAST模拟结果基本一致．验证了模拟边界条件和设置参数的准确性．后续可以用于模拟结构复杂的叶片定向凝固过程．指导实际生产工艺.     

液态金属冷却法制备工业燃气轮机涡轮叶片的研究进展

发电用工业燃气轮机涡轮叶片与航空发动机用叶片相比,在尺寸、运行环境及制备工艺方面都有很大的差异。文章介绍了用定向凝固技术中液态金属冷却（LMC）法,制备工业燃气轮机涡轮叶片的工艺及工艺参数、模拟技术方面的研究进展。     

重型燃机涡轮空心叶片定向凝固数值模拟

文章采用铸造模拟软件Procast,模拟了重型燃机涡轮空心叶片的定向凝固过程,研究了不同的抽拉速度对凝固时固液界面形态及铸件微观组织的影响,得到了较优抽拉速度.模拟结果表明,随着抽拉速度减小,固液界面趋于水平,定向柱晶分布均匀,取向良好.对模拟得到的较优抽拉速度进行试验验证,制备了具有较为理想的晶粒组织的实物叶片.     

A study on the fabrication of polycrystalline Si wafer by direct casting for solar cell substrate

Si-wafers for solar cells were cast in a size of 50 × 46 × 0.5 mm³ by a direct casting method. A graphite mold coated by boron nitride (BN) powder was used in order to prevent the reaction between carbon and the molten silicon. Without any coating, the reaction of the Si melt to the graphite mold was very severe. In the case of BN coating, SiC was formed in the shape of tiny islands on the surface of the Si wafer by the reaction between the Si-melt and the carbon of the graphite mold at high temperature. The grain size was about 1 mm. The efficiency of the Si solar cell was about 0.5% under AM1.5 conditions. It was lower than that of a Si solar cell fabricated with a common single- (sc, 3.0%) and poly-crystalline (pc, 1.0%) Si wafer, which showed much lower efficiency than that of other commercial pc- or sc-Si solar cell (10–15%).     

Crystalline silicon thin-film solar cells—recent results at Fraunhofer ISE

Crystalline silicon thin-film solar cells combine the advantages of the stability and high-efficiency potential of crystalline silicon solar cell technology with the low material utilization of the thin-film solar cell technology. At Fraunhofer ISE the wafer equivalent concept is currently pursued. Within this concept, the active silicon layers are deposited on high-temperature stable substrates. The resulting substrate/layer sandwich can be processed into a solar cell using the same techniques that are used in conventional crystalline silicon wafer solar cell processing, hence the name wafer equivalent. In the present paper we report on how we realized wafer equivalents and explain in detail our development work on processors for both large-area silicon deposition and for zone melting recrystallization. An overview is given on the solar cell results achieved in this area.     

Penetration of molten silicon into a bed of fines

During the casting process of silicon the mould must be buffered from the high temperatures of the molten silicon to prevent the mould melting and this is typically done by the operators laying down a layer of crushed silicon particles (fines) prior to pouring of the molten silicon. It is useful for operators to know how deep they should make the layer the fines so as to adequately separate the molten silicon from the mould. In this paper, we consider a model for the penetration of molten silicon into the pre-laid layer of silicon fines, which provides a predictive tool for estimating the necessary depth of fines in order to prevent the molten silicon touching the mould. The mathematical model developed here considers the flow of molten silicon as a Darcy flow and solidification due to heat flow as a one-phase Stefan problem. We are able to find a numerical solutions to this model, and from this we are able to extract data regarding the penetration depth of the molten silicon into the fines before solidification occurs. Our model and numerical solution can been seen as a first step toward understanding this important part of the casting process for silicon.     

铸造单晶硅性能和应用分析

以G6型多晶硅定向凝固铸锭炉生长的铸造单晶硅为研究对象,对其性能特点及应用进行分析.铸造单晶硅中含有位错、亚晶粒、多晶晶粒、间隙态元素和硬质点等缺陷.在铸造单晶硅制备过程中,因长晶界面不平及杂质存在的原因,硅锭生长时存在较大的应力,致使硅原子排列出现错排,从而导致位错、亚晶粒和多晶晶粒的产生,其中多晶晶粒的晶向主要有(...     

A simple process to remove boron from metallurgical grade silicon

It is necessary to develop solar grade (SoG) silicon for the photovoltaic industry. A desirable approach is to upgrade metallurgical grade (MG) silicon. The most problematic impurities to remove from MG silicon are B and P. A simple process to remove B from MG silicon has been developed by refining MG silicon in the molten state followed by directional solidification. With this approach, B has been reduced to 0.3 ppma, P to <10 ppma and all other impurities to <0.1 ppma using commercially available, as-received MG silicon. It remains to develop a similar P reduction process so that SoG silicon production from MG silicon can be commercialized. The B-removal process was applied to B overdoped electronic grade silicon, and the resulting material was used for crystal growth. Test solar cells of 12.5–13.4% (1 cm²) efficiency were produced.     

Large area multicrystalline silicon solar cells in high volume production environment—history, status, new processes, technology transfer issues

Cast multicrystalline silicon (mc-Si) solar cell technology, accounted for nearly 41% of all the PV modules manufactured worldwide in 2000. Since 1995 the use of cast mc-Si as a substrate has increased every year and that increase is expected to accelerate in the coming years as the PV market grows further. This impressive growth has been enabled by several factors—wafer suppliers, improvements in casting technology, sawing technology and cell process technology. In this paper the enabling factors will be discussed. The new processes used to enhance the efficiency of the cast multicrystalline silicon solar cells and the criteria for technology transfer will also be discussed.     

Electromagnetic continuous pulling process compared to current casting processes with respect to solidification characteristics

Electromagnetic continuous pulling (EMCP) process combines the advantages of the cold crucible melting (no pollution, no crucible consumption) with those of continuous casting (high material flow rate, uniform material structure and properties). It is compared to the usual casting techniques for massive crystalline silicon, i.e. directional solidification, Czochralski pulling, and floating zone pulling.The presentation is focused on technical productivity parameters, and on longitudinal distribution of impurities, typically oxygen and iron. This allows a semi-quantitative comparison between the 4 processes, having in prospect the use of a cheaper feedstock, together with the photovoltaic quality requirements.