【作者】 杨光红；

【导师】 杜祖亮；

【作者基本信息】 河南大学 ， 凝聚态物理， 2015， 博士

【摘要】 第一代硅太阳能电池是以高能耗、高污染为代价的生产加工方式来实现的。虽然具有高的效率,而在和传统化石类能源的市场竞争中处于劣势。主要原因在于发电成本太高。在保持效率的同时降低成本是太阳能电池是否取得市场竞争优势的关键。第二代太阳能电池致力于大规模生产,降低成本,薄膜化可以减少吸收层材料的使用量,降低成本的同时,又有利于光生载流子的分离与收集,提高光电转化效率。但第二代太阳能电池存在光吸收不足的问题;第三代太阳能电池主要是基于纳米结构太阳能电池,通过引入一些新的物理机制来实现太阳能转化效率的提高;采用低成本的加工手段或采用低品质的吸收层材料,使之纳米结构化等。太阳能电池由体材料、薄膜或超薄膜材料向纳米结构材料过渡的过程,正是大规模生产方式（roll-to-roll）逐渐实现,生产成本降低的过程。在这个过程中,存在许多问题需要解决。其中,与roll-to-roll大规模生产方式相匹配的可弯折透明导电电极的问题,新型薄膜材料的光吸收不足的问题是人们关注的热点。根据以上的问题,本论文做了以下三个方面的工作:1.针对铟锡氧化物（ITO）薄膜在roll-to-roll大规模生产方式应用中存在易碎性、在紫外/蓝色光谱范围的强吸收等缺点;我们特别研究设计了一种纳米结构金电极,其具有高透光、良好导电性、高功涵,良好的延展性,易于加工集成,和大批量生产方式的兼容性等优点。通过有限差分时域法,我们对金方形网孔电极的周期、线宽和高度对光学透过率的影响进行了全场模拟分析;根据优化的参数,采用电子束曝光方法制备了周期500 nm,高度50 nm,线宽60-100 nm的金网孔电极,在300到700 nm之间,金网孔电极测试的光学透过率约70%,700-1000 nm范围透过率超过80%。测试的光学透过率和计算结果一致。金纳米结构透明电极的光学透过率受到局域化表面等离子体共振吸收,表面等离子激元吸收,金反射等因素影响。测试的电阻率是商用ITO的两倍,约为74.5?/m2,远高于理论值,这主要和一些制备缺陷有关。本工作为金属透明电极的设计提供一些有益参考。2.面对新型薄膜太阳能电池的光吸收不足,特别设计了一种具有表面等离子体光吸收增强效应的银栅-超薄ITO复合上电极,用于超薄硅太阳能电池。二维十字型银栅网格被引入超薄铟锡氧化物中,超薄的铟锡氧化物薄膜主要起到收集光生电荷、减反射膜的作用,二维银栅扮演着电荷输运和光吸收增强的作用。有限时域差分模拟结果表明,优化的银栅-铟锡氧化物复合上电极太阳能电池获得61%的光吸收增强。超薄硅支持法布里-珀罗共振模,二维银栅引入了波导模、局域化表面等离子体共振模、表面等离子激元,多种效应种协同促进超薄硅的光吸收增强。3.背衬底金属纳米结构能够耦合垂直入射光进入横向传播的表面等离子激元模,从而实现光路径的增加及光吸收增强。本章设计了一种正六边形凸起金结构,采用电子束曝光的工艺流程制备了金结构阵列,并以此为结构化的背衬底,用以增强薄膜Cu₂O-Zn O太阳能电池的光吸收。结果表明,引入凸起结构后造成了Cu₂O-Zn O pn结界面质量变差,缺陷复合增多,增加反向饱和暗电流,导致开路电压降低;同时由于Cu₂O的有效吸收范围小于650 nm,而纳米结构化背电极支持的表面等离子激元模不在此范围内,造成整个电池的短路电流没有提高。金属纳米结构的表面等离子体共振吸收增强的过程存在着欧姆吸收损失的特征,需要对结构进行合理的设计,才能实现光吸收增强及效率提高。本论文的创新点主要包括:针对当前新型薄膜太阳能电池所面临的问题,一是能够匹配大规模生产方式的柔性透明电极的设计和制备技术,二是新型薄膜电池不充分的光吸收。首先开展了金属纳米结构透明电极的理论计算模拟和实验研究,并在此基础上,通过理论计算模拟,设计了一种具有表面等离子体光吸收增强效应的银栅-ITO复合电极;采用电子束曝光的方法制备了正六边形凸起金属结构,研究了其在氧化亚铜太阳能电池中的表面等离子体光吸收增强作用。光学理论模拟和实验的结合,是本文的特色和创新点所在。更多还原

【Abstract】 The first generation silicon solar cells were fabricated and achieved by the production processing method at the expense of environmental pollution,high energy consumption,despite their high efficiency,they are in disadvantageous state in market competition Compared with the traditional fossil energies due to high power generation cost.Cost reduction is the key whether or not the first generation silicon solar cells obtain competitive advantage in the market.Second generation solar cells have characteristic of mass production in order to reduce costs.Thin film solar cell can not only reduce the use of the absorption material amount,which is suitable to mass production,but also be conducive to the separation and collection of photogenerated carriers,improve the photoelectric conversion efficiency.But the second generation solar cells still have the problem of insufficient light absorption.The third generation solar cells are mainly based on nanostructured solar cells.Some new physical mechanisms are introduced to increase the solar energy conversion efficiency by means of low cost processing or use of low quality absorption material,or some nanostructures etc.The development process of solar cells from bulk materials,film or thin film material to nanostructured materials is also a process to realize the roll-to-roll mass production and production cost reduction.Many problems in the process are essential to resolve.One problem is a bendable transparent conductive electrode compatible with the roll-to-roll mass production;another problem is the insufficient light absorption problem of film or thin film solar cells.According to the above problems,this thesis consists of three aspects:1.The drawbacks of traditional ITO films such as its brittleness and strong absorption in the UV/blue spectral range make them unsuitable to the roll-to-roll mass production in solar cells and LEDs;Nanostructured metal square mesh electrode have favorites such as high optical transparency,good electrical conductivity,mechanical flexibility,easy machining and compatibility with the mass production style.by using the finite-difference time domain method,the effects of the period,linewidth and height of Au square mesh electrode on the spectrum transmittance were firstly analyzed and then Au square mesh TCEs with the 500 nm in period,70 nm in height and line width ranging from 60 to 100 nm were fabricated by using EBL technique.The measured results showed that the optical transmittance of the TCEs is about 70% in the 350-700 nm wavelength range and over 80% in the 700-1000 nm range,which accord with the theoretical simulation results.Optical transmittance is affected by localized surface plasmon resonance（LSPR）,surface plasmon polarizations（SPPs）and the reflection of Au nanostructures.The measured surface resistivity of the TCEs with the 500 nm in period,50 nm in height and 50 nm in linewidth is about 74.5 ?/m2 due to fabrication drawbacks.2.A novel nanostructured Ag crossing grid-ITO composite front electrode with plasmonic light absorption enhancement is designed to resolve inadequate light absorption problem in ultrathin film c-Si solar cells.In this structure,the ultrathin ITO layer is mainly used to collect charge and Ag crossing grids work as a charge transportation path and an optical absorption enhancer.According to the defined absorption enhancement factor G,structural parameters,such as ITO film thickness,linewidth,height and period of Ag grid,were systematically optimized using finite-difference time-domain stimulations,and absorption enhancement mechanisms were analyzed.A 61% light absorption enhancement is observed for the c-Si solar cell with Ag crossing grid in composite front electrode compared to that without Ag crossing grid.Four types of resonance modes such as Fabry–Perot modes,waveguide,localized surface plasmon resonances and surface plasmon polaritons are supported by the designed structure.FP modes may be excited in bare c-Si SCs,but the inclusion of 2D Ag crossing grid introduces waveguide sandwiched by Ag grids and Ag back electrode,SPPs and LSPR modes that lead to enhanced light absorption.3.Nanostructured metal back electrode can couple vertical incident light into surface plasmon polaritons mode with the lateral propagation path and enhance light absorption.In this part,Au regular hexagonal ridge arrays are fabricated using EBL method and are used as nanostructured metal contact electrodes for the Cu₂O-ZnO solar cells in order to enhance light absorption of thin Cu₂ O film.The introduction of nanostructure in back metal contacts results in the deteriorating interface quality so that open circuit voltage cut down.The Only optimized metal nanostructures may be beneficial to LSPR absorption enhancement in thin Cu₂ O absorber.In this structure,SPPs coupling of incident light occur at wavelength larger than 650 nm and do not contribute to the effective absorption of Cu₂ O.According to the existing problems in novel thin film solar cells,one is a technology of the design and fabrication of flexible transparent electrode suitable for the large-scale production;another is the inadequate absorption enhancement in thin film solar cells.Firstly,the theoretical calculation and experimental research are launched on a metal nanostructured transparent electrode.And on this basis,a novel nanostructured Ag grid-Indium Tin Oxide（ITO）film composite front electrode with plasmonic light absorption enhancement is designed through the FDTD calculations.A regular hexagon convex metal nanostructure was prepared by the method of electron beam lithography and their light absorption enhancement in the Cu₂ O solar cells were investigated in details.Optical theory simulation and experiment combination are the main innovation points of this thesis.更多还原