低缺陷密度大单晶比例太阳能级类单晶硅锭制备及其表面制绒研究

发布时间：2017-12-27 22:33

本文关键词：低缺陷密度大单晶比例太阳能级类单晶硅锭制备及其表面制绒研究　出处：《苏州大学》2016年博士论文　论文类型：学位论文

【摘要】：类单晶籽晶辅助定向凝铸法是近年来在多晶硅籽晶辅助定向凝铸法基础上发展起来的一种全新的低成本、高效率类单晶硅锭制备技术。该技术具有单炉生产量大,单位质量能耗低,硅锭质量好等优点,其对应的太阳能电池片相对于多晶片转换效率更高。但是,现有制备技术存在单锭单晶比例低,缺陷密度高,无法进入产业化阶段的问题;同时,由于其表面单晶与多晶晶粒共存,一般的酸、碱腐蚀法对其制绒都存在困难。为了制备可产业化的低缺陷密度大单晶比例类单晶硅锭及提升对应太阳能电池的效率,本文使用适合产业化的定向凝铸炉,进行了多晶硅锭和类单晶硅锭的制备技术优化和生长机理分析,并对制备的类单晶太阳能电池片表面制绒技术进行了研究。采用的美国GT公司G6-850定向凝铸炉具有目前世界最先进的双电源双加热器结构,热场比较均匀,适合G6(即单炉生产硅锭可切割出36个156×156mm2的硅晶柱)及更大尺寸硅锭产业化生产。本文首先进行了多晶硅籽晶辅助定向凝铸技术优化研究。实验表明:籽晶辅助定向凝铸工艺制备的多晶硅锭从底部到顶部的缺陷密度分布状态可以分为准直线平坦区和准线性增加区。在直线区中,硅锭缺陷密度基本保持不变或微弱增加;准线性区中,硅锭缺陷密度随着高度的增加而准线性增加。随着结晶降温速率减小,硅锭的缺陷密度整体降低,直线区变长,准线性区变短,对应太阳能电池转换效率高于18%的比例增加。为了克服籽晶层局部过熔现象,本论文创新地设计了一种缓冲式籽晶熔化控制技术。缓冲层位于籽晶层上,由小颗粒的原生多晶硅料层和其上的晶砖层构成。采用缓冲式籽晶熔化控制技术制备多晶硅铸锭的实验表明:该技术可以有效避免因硅熔液从硅料间隙渗下造成的籽晶层局部过熔现象,提高了籽晶层的熔化均匀性,延长了硅锭中低缺陷密度直线区的长度,降低硅锭底部红区(即少子寿命低于2μs的区域)的高度,提高了硅锭质量,为超薄籽晶层定向凝铸工艺产业化奠定了基础。采用单晶硅籽晶辅助,我们研究了定向凝铸工艺制备类单晶硅锭的制备工艺。G6类单晶铸锭实验结果与多晶硅实验基本一致,即结晶降温速率下降,硅锭缺陷密度整体降低,直线区变长,准线性区变短。通过类单晶铸锭实验发现,当降温速率较大,即降低温度/结晶时间的比例为0.467时,类单晶硅锭中单晶比例约为61%;当降温速率较小,即降低温度/结晶时间的比例为0.154时,类单晶硅锭中单晶的比例可以达到75%以上,这一比例对产业化来说,已具有应用价值。在类单晶缓冲式籽晶熔化控制技术装料铸锭的基础上,发展了缓冲层中心低四周高凹陷式类单晶缓冲籽晶熔化控制技术。实验结果表明:该装料方式克服了坩埚中心熔化过程中温度较低,坩埚四周熔化过快的问题,硅熔液通过缓冲层后,形成了更为平直的固液面,与籽晶层实现了良好的接触。该技术克服了类单晶硅片中十字纹的形成。最终实验制备出单晶比例高达87.5%的产业化类单晶硅锭,具有较高的应用价值。定向凝铸硅锭顶部和底部的红区降低了硅锭的硅片有效切片数。本文通过类单晶和多晶硅的定向凝铸工艺实验,研究了硅锭中红区的形成机理。通过不同结晶工艺温度实验发现,硅锭底部红区的高度受到硅熔液温度的影响,硅溶液温度越高,红区的高度越低。通过对铸锭结晶工艺降温速率的实验研究表明,随着降温速率的降低,红区高度降低。基于实验结果我们提出:硅锭底部红区受到硅熔液中温度梯度的影响。温度梯度越大,在铸锭初期越易生长小晶粒,从而形成了大量的位错和晶粒间界,成为了杂质的吸附中心,降低了硅锭底部晶体的载流子的寿命,形成硅锭底部红区。缓冲式籽晶熔化控制技术实验表明硅料熔化时较为平直的固液面避免了籽晶层局部过熔,提高了硅熔液温度,从而降低了红区高度。类单晶硅片因其制绒效果差,限制了其在太阳电池中的应用。本文创新地采用了两步腐蚀法制备纳米绒面结构的类单晶太阳电池,有效提高了电池的光吸收率和载流子寿命。实验结果表明:从硅晶柱底部到顶部的类单晶电池转换效率均获得了提高。两步腐蚀法制备的类单晶太阳电池的转换效率从酸腐蚀的18.4%提高到了18.9%,并且减少了电池上的色差。通过亚电池并联模型很好的解释了类单晶电池的性能取决于最差亚电池的性能。本文制备的类单晶电池的转换效率远超过了传统高效多晶电池18.0%左右。
[Abstract]:The class of single crystal seed assisted directional solidification method is a new low cost, in recent years in the polysilicon seed assisted directional tracing method based on the development of efficient class of single crystal silicon ingot preparation technology. The technology has the advantages of large volume of single furnace production, low unit mass energy consumption and good quality of silicon ingot, and its corresponding solar cell chip has higher conversion efficiency than multi chip. However, the existing preparation technology has low single crystal single crystal ratio and high defect density, and can not enter the industrialization stage. At the same time, because of the coexistence of single crystal and polycrystalline grain on the surface, the general acid and alkali corrosion method has difficulty in making the pile. For the low efficiency of large single crystal defect density ratio can be prepared in the industrialization of the class of monocrystalline silicon ingots and enhance the corresponding solar cell, this paper combines the use of directional furnace for industrialization, analyzes the polysilicon ingots and silicon ingots class preparation technology optimization and growth mechanism, and the preparation of single crystal like solar cell surface cashmere is studied. Double power is currently the world's most advanced double heater with American GT company G6-850 directional combines furnace, thermal field is relatively uniform, suitable for G6 (i.e., a single furnace production of silicon ingot cutting silicon crystal column 36 156 x 156mm2) and large size silicon ingot production. This paper combines the technology of polysilicon seed assisted directional optimization research. Experimental results show that the seed polysilicon assisted directional preparation combines the ingot from the bottom to the top of the defect density distribution can be divided into quasi linear and quasi linear increase in flat area. In the straight line, the defect density of the silicon ingot remains unchanged or slightly increased; in the quasi linear region, the density of the defects in the silicon ingot increases linearly with the increase of height. With the decrease of crystallization cooling rate, the defect density of silicon ingot decreases, the linear area becomes longer, and the Quasilinear zone becomes shorter, which corresponds to the increase of solar cell conversion efficiency over 18%. In order to overcome the phenomenon of partial melting of the seed layer, a new technique for controlling the melting of seed grain was designed in this paper. The buffer layer is located on the seed layer, consisting of a small particle's primary polysilicon layer and a brick layer on it. The buffer type seed melting control technology of preparation of polycrystalline silicon ingot experiment shows that this technology can effectively avoid molten silicon from silicon material clearance caused by seepage under the seed layer partial melting phenomenon, improve the melting of the seed layer uniformity, low defect density of silicon ingot to extend the length of straight line, reduce at the bottom of the ingot red zone (i.e., the lifetime of less than 2 mu s area) height, improve the quality of the ingot, laid the foundation for the thin seed layer orientation combines the industrialization process. The seed of single crystal silicon, we studied the directional preparation process combines the class preparation process of single crystal silicon ingot. The experimental results of G6 single crystal ingot are basically the same with that of polysilicon experiment, that is, the cooling rate of crystallization decreases, and the density of silicon ingot decreases as a whole, and the linear region becomes longer and the quasi linear region becomes shorter. The monocrystalline ingot is found when the cooling rate is larger, the lower the temperature / crystallization time ratio of 0.467, class of single crystal silicon ingots in the proportion is about 61%; when the cooling rate is smaller, lower temperature crystallization time ratio of 0.154, the proportion of single crystal silicon ingots in class can reach more than 75%, the a proportion of industrialization, has application value. On the basis of single crystal buffer seed melting control technology, loading and casting ingots, a high concave single crystal buffer seed melting control technology is developed for the center of the buffer layer. The experimental results show that the charging method overcomes the problem of low melting temperature and melting too fast around the crucible, and forms a more straight solid liquid surface after the silicon melt passes through the buffer layer, which achieves good contact with the seed layer. The technique overcomes the formation of the cross pattern in the monocrystalline silicon. In the final experiment, the industrial monocrystalline silicon ingot with a high ratio of 87.5% is prepared, which has high application value. Directional solidification of silicon ingot at the top and bottom of the red zone reduces the effective number of silicon ingot slicing of silicon wafer. This paper combines the technology of directional experiment by single crystals and polycrystalline silicon, the formation mechanism of the red area in the study of silicon ingot. It is found that the height of the red region at the bottom of the silicon ingot is influenced by the temperature of the molten silicon, and the higher the temperature of the silicon solution, the lower the height of the red region. The experimental study on the cooling rate of the ingot crystallization process shows that the height of the red region is reduced with the decrease of the cooling rate. Based on the experimental results, we suggest that the red region at the bottom of the silicon ingot is affected by the temperature gradient in the silicon melt. The greater the temperature gradient, the easier the growth of small grains in the initial stage of the ingot, resulting in a large number of dislocation and grain boundaries, which become the adsorption centers of impurities, and reduce the lifetime of carriers at the bottom of the ingot, forming the red area at the bottom of the ingot. The experiment of buffering seed melting control technology shows that the relatively straight solid liquid surface melts the silicon material and avoids the local overmelting of seed layer, and improves the temperature of silicon melt, thereby reducing the height of red zone. The application of the monocrystalline silicon chip is limited in the solar cell because of its poor cashmere effect. In this paper, the two step corrosion method is used to prepare the single crystal solar cell with nano suede structure, which can effectively improve the light absorption and carrier life of the battery. The experimental results show that the conversion efficiency of the single crystal cell from the bottom to the top of the silicon crystal column has been improved. The conversion efficiency of the single crystal solar cell prepared by the two step corrosion method increased from 18.4% of acid corrosion to 18.9%, and the chromatic aberration on the battery was reduced. Through the sub cell parallel model can well explain the properties of single cell performance depends on the subgrain cell. The conversion efficiency of the single crystal cell prepared in this paper is far more than 18% of the traditional high performance polycrystalline battery.
【学位授予单位】：苏州大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN304.12

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