基于有序硅纳米线阵列结构的新型异质结太阳电池的研究

As a new third generation solar cell should have the following characteristics: low cost, high efficiency, long life, abundant material source, non-toxic and so on. At present, the cost of traditional crystalline silicon solar cells remains high because of high quality requirement in crystal silicon wafer; Although amorphous thin film silicon can reduce the cost of solar cells, its efficiency is low and there is degradation effect. So the development space of amorphous thin film silicon was inhibited. Therefore, this project will develop the high stability, low cost, high performance solar cells key materials based on silicon nanowire array structure. The device model of "aluminium back electrode / silicon nanowires / silicon / aluminum doped zinc oxide transparent window electrode" was proposed. This model uses a rich source of silicon as the main raw material, and large area of nanowire array structure was fabricated on low quality of the single crystal silicon by chemical etching. Through the research in this project, the formation mechanism of electrodeless chemical etching method assisted by metal nanoparticles was fully revealed. The charge separation, transport and composite mechanisms of p-n junction based silicon nanowire arrays heterostructure were also revealed. Finally, the high-efficiency solar cell model based silicon nanowire arrays was established. The problems of carrier surface recombination rate enhancement and battery series resistance overlarge were solved. It is beneficial for the next generation development of monocrystalline silicon and silicon-based films solar cells to provide scientific basis and technical foundation.

作为新型第三代太阳电池应具有如下特征:低成本、高效、长寿命、材料来源丰富、无毒等特点。目前，由于传统晶硅太阳电池对晶硅品质要求高，成本居高不下；而非晶硅薄膜太阳电池虽能降低成本，但其效率低且存在衰退效应，也抑制了发展空间。因此，本项目将发展高稳定、低成本、高效硅纳米线阵列结构太阳电池的关键材料，提出"铝背电极/硅纳米线/硅薄膜/掺铝氧化锌透明窗口电极"模型。本研究中将低品质的单晶硅通过化学刻蚀法制备出大面积硅纳米线阵列结构，全面揭示金属纳米颗粒辅助无电极化学刻蚀法制备硅纳米线阵列形成机理，以及硅纳米线阵列异质结构PN结的电荷分离、输运和复合机理，建立高效硅纳米线阵列结构的太阳电池模型，解决载流子表面复合速率增强和电池串联电阻过大等问题。为当前占据太阳电池主导地位的单晶硅太阳电池和硅基薄膜太阳电池的下一代发展提供科学依据。

光伏技术被认为是能够避免全球发生能源大危机以及环境大污染的主要途径。目前，由于硅基太阳电池涉及的昂贵制备费用使得大范围采用光伏发电变得不可能。不过硅纳米线径向结电池由于具有优良的减反性能以及独特高效的载流子分离机制，被认为在实现高效与低成本电池方面具有较为广阔的发展前景。所以对有序硅纳米线阵列结构的新型异质结太阳电池的研究显得十分有意义。本课题主要研究工作如下：.（1）采用了金属辅助化学刻蚀法制备纳米线阵列，通过研究刻蚀时间对纳米线尺寸形貌的影响规律，实现了长度可控的硅纳米线阵列。.（2）利用等离子体化学气相沉积（PECVD）技术在纳米线上沉积氢化非晶硅薄膜，制备径向p-n结。研究了纳米线上非晶硅的沉积形貌，结果表明：一方面随着纳米线长度增加，长径比增加，越不容易在整根纳米线上形成径向结；另一方面随着非晶硅沉积时间的增加，反应物逐渐向下迁移扩散，形成完整径向p-n结。.（3）研究了纳米线上AZO薄膜的沉积形貌，从而发现了通过金属辅助化学刻蚀法制备的纳米线较密集，间隙较小，溅射的AZO不能覆盖住整根纳米线，为此，实验过程通过采用氢氧化钾刻蚀纳米线，形成纳米尖锥形貌，减小了纳米线间隙，再溅射AZO后实现了硅纳米线/硅薄膜上AZO薄膜的共形沉积，并在纳米线底部连接成膜。.（4）为了减小纳米线表面复合，实验过程中采用PECVD在纳米线表面沉积本征氢化非晶硅薄膜以钝化硅表面。但是薄膜性能极大地依赖于薄膜沉积条件，因此论文研究了硅烷浓度与沉积气压对薄膜性能的影响规律，确定了薄膜制备的最佳工艺方案。.（5）通过比较有无本征钝化层的纳米锥太阳电池，发现实验中通过加入本征氢化非晶硅，电池开路电压有了较大提高，电池效率有较大改善。再比较了平面p-i-n结太阳电池，纳米线p-i-n结太阳电池与纳米锥p-i-n结太阳电池后，发现纳米锥p-i-n太阳电池性能最优，这一方面是由于它具有较高的减发射能力，增加了光吸收，另一方面是由于它具有独特的径向分离机制。