高晶化率立方相微晶碳化硅薄膜材料的低衬底温度（<350度）制备与生长机制研究

Due to its significant advantages in cell performance and deposition process, silicon heterojunction (SHJ) solar cell is of highly both scientific and industrial interest. The design, adjustment and improvement of the optical properties of window layers for SHJ cells has a very high potential for a further increase of the efficiency. Compared with conventional p-type or n-type amorphous silicon, or amorphous silicon carbon alloys, silicon carbide in crystalline form is on the top of the list as the window layer material. Unfortunately this material in crystalline form is prepared at high temperatures (>800°C), completely out of the range for thin film applications on SHJ cells. In this work, Hot-Wire Chemical Vapor Deposition (HWCVD) technique will be utilized for the deposition of highly crystalline silicon carbide thin films in stoichiometric form at low substrate temperature (<350 °C). The growth mechanism of silicon carbide crystallites on silicon substrate, as well as the correlation of its microstructure with film material property, will be systematically studied. The optimized highly transparent and conductive microcrystalline silicon carbide films will be applied in silicon heterojunction solar cells as window layers. The interface at the microcrystalline silicon carbide window layer and silicon substrate will be investigated combining with the study of the band structure in cells and the carrier transportation mechanism. The SHJ cell configuration will be optimized for adopting the highly transparent microcrystalline silicon carbide window layer for higher cell efficiency, promoting the industrial application of SHJ solar cells.

单晶硅异质结（SHJ）太阳电池由于其在制备工艺和电池性能上的诸多优势成为学术和产业应用研究热点，而窗口层材料的选择和设计是提高SHJ电池转换效率的关键。宽禁带碳化硅晶体由于其优良的透光性成为理想的窗口层材料。然而晶体碳化硅传统制备温度通常高于800°C，无法适用于硅基太阳电池工艺。本项目拟采用热丝化学气相沉积法实现低衬底温度 (<350度) 制备高晶化率立方相微晶碳化硅薄膜材料，系统剖析微晶碳化硅窗口层材料的微相结构、窗口层与衬底的界面结构和单晶硅异质结太阳电池光电性能的內秉关系，解析热丝化学气相沉积制备微晶碳化硅窗口层材料在单晶硅衬底表面的形核生长机制，寻求兼具优良光学和电学性能的微晶碳化硅窗口材料的有效构筑，实现电池转换效率的提高，为推动单晶硅异质结太阳电池的产业化应用提供关键理论支撑。

碳化硅晶体材料是一种宽禁带半导体材料，具有优良的透光性和导电性，是太阳电池的理想窗口层材料之一。在衬底温度小于350 °C的条件下制备碳化硅晶体材料在科学研究和生产应用上都具有重要意义。本项目研究了热丝化学气相沉积法制备碳化硅薄膜的材料性能、制备工艺及生长机理。为了获得兼具优良光学和电学性能的碳化硅窗口材料的有效构筑，综合微晶碳化硅拉曼（Raman）图谱和碳化硅红外特征吸收峰的分析，提出了红外晶化率和3C-SiC组分比例计算法，解析了立方碳化硅薄膜生长机制，系统剖析了材料微结构及其光电性能內秉关系。研究表明本项目中碳化硅薄膜材料的晶化率大于80%且以立方碳化硅（3C-SiC）为主。材料中3C-SiC晶相生长受热丝化学气相沉积中氢气浓度、热丝温度和衬底温度的影响较显著。3C-SiC组分的增加有利于微晶碳化硅薄膜材料透光性的增加。通过优化调控3C-SiC晶相生长，在衬底温度为275 °C的条件下获得了光学带隙为3.2 eV且电导率约为0.1 S/cm的高晶化率3C-SiC薄膜窗口层材料。SiC/Si界面是3C-SiC窗口层材料在硅太阳电池应用的关键之一。在SiC/Si界面的非晶孵化层阻碍了太阳电池中光生载流子的有效传输和收集。为此我们采用硅烷浓度渐变工艺有效地抑制了SiC/Si界面处非晶孵化层的厚度。得益于微晶3C-SiC材料的高透光性及其在窗口层光学结构中光学折射率匹配，硅太阳太阳电池的光生电流密度提升了2 mA/cm2。本项目研究为宽带隙3C-SiC薄膜的低温制备及其在硅太阳电池的产业化应用提供了关键理论支撑和实验基础。