【作者】 肖俊峰；

【导师】 汪雷； 杨德仁；

【作者基本信息】 浙江大学 ， 材料物理与化学， 2010， 硕士

【摘要】 作为太阳能利用的重要组成部分,光伏发电是一种清洁的、用之不竭的可再生绿色新能源,受到越来越多的关注。近年来全球光伏产业发展速度迅猛,而我国光伏产业规模已经稳居全球第一。但是,国内相关的科学研究还很缺乏,技术积累薄弱,阻碍了光伏产业的进一步发展。因此,开展此方面的基础研究具有重要的科学意义和应用价值。目前,晶体硅（包括单晶硅、多晶硅和带硅等）太阳电池占光伏产业市场份额的90%以上,在2020年之前,晶体硅太阳电池的统治地位难以撼动。由于硅材料成本居高不下,减薄硅片厚度成为降低电池生产成本最有效的手段。在硅片变薄的同时,对光吸收效率和表面钝化的要求也增加了。增强光吸收对保持薄片晶体硅太阳电池的性能稳定和进一步提升转换效率十分重要。围绕晶体硅太阳电池的光吸收问题,本文进行了一系列研究,包括表面损伤对单晶硅制绒的影响,多孔硅的生成以及形貌调控,新型的多孔-金字塔结构的设计与优化。得出了如下结论:1.硅片表面损伤较严重时,在制绒的过程中硅片表面金字塔结构的长大很不规则;硅片表面损伤较轻时,金字塔结构的长大相对规则。在80℃下20wt%KOH的溶液中处理40s后,进行60min的制绒处理能得到较好的反射性能,同时可将硅片表面损伤完全去除,这样能减少腐蚀过程对硅片的总消耗量。2.在50℃下5M HF+0.14M Fe（NO₃）₃溶液中反应,硅片表面容易得到杂乱的多孔结构。增加HF和Fe（NO₃）₃的浓度,能够得到腐蚀凹坑内密布多孔结构的表面形貌。在50℃下10M HF的溶液中,将Fe（NO₃）₃的浓度从0.2M增加到0.4M时,腐蚀凹坑内的多孔结构转变为微小的突起,导致表面反射率值急剧增大。3.在HF/Fe（NO₃）₃溶液中加入AgNO₃可以在硅片表面沉积银颗粒,进而增强Fe³⁺得到电子的能力,并加速还原反应的进行,极大的增加单晶硅片表面多孔结构的覆盖率和均匀性。当沉积的银颗粒较多且连接在一起时可以腐蚀得到纳米硅丝,银颗粒分散则可腐蚀得到深孔结构。4.在多晶硅表面制作多孔硅结构以及沉积氮化硅薄膜均能够得到非常好的减反射效果,在多晶硅表面生成的多孔硅在大范围内比较均匀,而在晶界等表面缺陷处生成排列整齐的孔状结构。在没有金属颗粒辅助的情况下,抛光的硅片表面难以生成均匀的多孔结构。5.在多孔-金字塔结构制作中,二次腐蚀时间为30min时,金字塔基本保留,硅片表面反射性能达到最好。随着在HF/Fe（NO₃）₃溶液中反应时间的增加,硅片的少子寿命降低。综合考虑反射性能和少子寿命,经过60min金字塔织构化后,在50℃下10 M HF+0.2 M Fe（NO₃）₃溶液中二次腐蚀30min的效果最佳。6.二次腐蚀采用HF/Fe（NO₃）₃/AgNO₃的腐蚀液能增加金字塔结构的多孔化反应速度,减少与溶液中Fe离子的接触从而减少沾污。硅片表面生成的多孔硅均匀性很好,且反射性能优异。更多还原

【Abstract】 As a clean and inexhaustible reproducible green energy, photovoltaics （PV） is an important part of the utilization of solar energy and has drawn extensive attention. PV market and corelative application increased drastically. In China, a world-shaking growth of PV industry has been witnessed. The output had been the first in the world since 2007. However, domestic studies on relative science are still short and technology accumulations are relatively devoid. The lack of technology hinders the further development of PV industry. Therefore, basic studies on PV have imperative scientific significance and application value.Presently, crystalline silicon solar cells which accounts for more than 90% of all kinds of solar cells are the dominator of PV market. According to a matter of speculation, crystalline silicon solar cells will still be the dominator of PV market before 2020. Because of the high cost of silicon materials, silicon wafers are getting thinner and thinner for effective cost reduction. Utilization of thin wafer increases the request for light absorption and surface passivation. Light absorption is imperative to keep the property of silicon solar cells stable and to improve conversion efficiency. We have studied influence of subsurface damage on texturing of monocrystalline silicon wafers for solar cells; fabrication of PS layer and control the morphology of PS layer; designation and optimization of porous-pyramid structure. The conclusions are the following:1. "Pyramid" grew irregularly during the texturing process when the subsurface damage is serious. Otherwise, "Pyramid" grew regularly when the subsurface damage is light. Silicon wafer can show fine reflected property when it was textured 60 min in 3wt% KOH and 8vol% IPA alkali solution after reacted at 80℃for 40s in 20wt% KOH solution. The subsurface damage can be removed completely. Reduction of dissipating silicon can be carried out in the chemical etch process.2. Disordered porous silicon layer was obtained on silicon wafer by stain etch in 5 M （M = mol L-1） HF and 0.14 M Fe （NO₃）₃ solutions at 50℃±1℃. Corrosion pits which filled with porous silicon was gained by increasing the etchant to 10M HF and 0.2M Fe （NO₃）₃. Porous silicon changes to pillar-like structures which will increase reflectivity of silicon wafer when oxidant increases from 0.2M to 0.4M.3. Addition of AgNO₃ to HF / Fe（NO3）₃ solution can remarkably improve the uniformity and covering scale of PS layer on silicon wafer because of the deposition of silver particles on silicon surface can attract electrons and accelerate the cathode reaction. Silver particles link with each other will results in formation of silicon nanowires. PS layers were obtained when silver particles are dispersed.4. Both PS layer and SiN_x film can work as anti-reflection coating and reduce surface reflectivity of polycrystalline silicon. PS layers were uniform at wide range of polycrystalline silicon surface. While orderly deep porous texture was formed at the neighborhood of grain boundaries. It’s difficult to form uniform PS layers on polished silicon surface without metal catalyst.5. Pyramids were reserved and reflectance property was fantastical when second etching time is 30min during the fabrication process of porous-pyramid texture. Effective lifetime of silicon wafers reduces gradually as etching time increases. After textured for 60 min in KOH/IPA solution, the optimal etching time for silicon wafer is 30 min in 10M HF/0.2M Fe （NO₃）₃ solutions when both reflectance and effective lifetime are considered.6. Pyramid textured silicon wafer etched in HF/Fe （NO₃）₃/AgNO₃ solutions can accelerate the etching reaction and improve the uniformity of PS layers. The reflectivity of porous-pyramid textured silicon is small. The reduction of reaction time can effectively reduce iron contamination.更多还原