【作者】 胡昱；

【导师】 何建军；

【作者基本信息】 浙江大学 ， 光通信， 2014， 博士

【摘要】 世界上最丰富的可再生能源就是太阳能,而对太阳能高效利用最有前景的一种方式是太阳能电池。太阳能电池从发明到现在,已经有200多年了。然而太阳能电池在能源领域的应用却依然无法与传统能源所抗衡。阻碍太阳能电池大规模应用的原因主要有两个：相对较低的光电转换效率和较高的制造成本。为了解决这两个问题,目前有大量的研究工作围绕纳米结构的太阳能电池而展开,以提高太阳能电池的表现。本文研究的第一个对象是纳米线太阳能电池。纳米线是直径在几十到几百纳米,长度为数微米的半导体圆柱。它有非常好的减反射效果。本文将有限元方法应用于纳米线光学特性的理论计算,建立了纳米线的光学模型。本文对同质结与异质结纳米线的光学特性分别进行了研究。本文首先利用有限元方法求解麦克斯韦方程组,计算得出GaAs同质结纳米线的反射率、透射率和吸收率。模型的反射率模拟结果与刻蚀制作的GaAs纳米线反射率实验结果进行了比对。模型的反射率模拟结果与VLS生长制作的GaAs纳米线反射率实验结果也进行了比对。在AM1.5G太阳光光谱条件下,本文计算得出了让电池吸收率和产生的短路电流达到最大的纳米线直径,周期(纳米线间距)与长度。本文计算了纳米线顶端的Au颗粒(VLS生长纳米线时产生的)对电池最大电流密度的影响。本文计算了纳米线之间填充的有机物与ITO透明电极对电池最大电流密度的影响。纳米线光学模拟的另一个研究重点是AM1.5G条件下,Si衬底上异质结纳米线光学特性的数值模拟。本文计算了直径在100n m一250nm之间、周期在250-1000nm,长度为5μm的双结纳米线光生电流密度。本文研究了纳米线的禁带宽度对于光生电流密度的影响。本文计算了Si衬底上不同禁带宽度的纳米线在满足电流匹配条件下的最佳直径与周期。本文根据模拟得到的纳米线直径与周期,结合电子束曝光与感应耦合等离子体刻蚀的方法,在GaAs衬底上制作了GaAs纳米线。本文另一个研究对象是纳米结构菲涅尔透镜。本文将有限元方法应用于纳米结构菲涅尔透镜光学特性的理论计算,建立了纳米结构菲涅尔透镜的光学模型。本文利用有限元方法求解麦克斯韦方程组,计算得出菲涅尔透镜阵列的反射率、透射率和吸收率。本文将纳米结构菲涅尔透镜阵列应用于Ⅲ-V族叠层太阳能电池,研究了菲涅尔透镜对电池反射率与吸收率的影响。根据模拟得到的菲涅尔透镜尺寸,结合电子束曝光(EBL)与感应耦合等离子体(ICP)刻蚀的方法,在Ⅲ-V族叠层太阳能电池上制作了纳米结构菲涅尔透镜阵列。最后,本文测量了制作了菲涅尔透镜阵列电池片的I-V曲线等特性。更多还原

【Abstract】 The most abundant source of renewable energy is solar energy.The most promising way to use solar energy efficiently is solar cell. It has been more than two handred years since solar cell was invented. But solar photovoltaic cells are not competitive with more conventional energy technologies because of their relatively low photoconversion efficiency and high cost. A substantial body of recent work in photovoltaics is beginning to exploit intentionally engineered nano-and micro-scale structures and the physics of reduced dimensionality to increase device performance.One focus of this thesis is nanowire(NW) solar cells. NWs are rods with a length typically on the order of microns and a diameter on the order of10’s to100’s of nanometers. It is well known that NWs can exhibit anti-reflection properties that are less dependent on incident wavelength, polarization and angle as compared to conventional thin film dielectric coatings. The reflectance, transmittance and absorptance of GaAs nanowire (NW) arrays are calculated by solving Maxwell’s equations using the finite element method. The model is compared with measurement results from well-ordered periodic GaAs NW arrays fabricated by dry etching. The model results are also compared with the reflectance measured from NWs grown by the Au-assisted vapor-liquid-solid (VLS) method. The optimum NW diameter, periodicity (spacing between NWs) and length are determined to maximize absorptance of the AM1.5G solar spectrum and short circuit current density in a NW array solar cell. A gold nanoparticle at the top of the NWs (used in the vapor-liquid-solid NW growth process) substantially reduced the optimum photocurrent density, while a polymer filling the space between NWs and a planar ITO contact had a relatively minor influence. Numerical simulation of the photocurrent density is performed for a two-junction nanowire (NW) on silicon solar cell under AM1.5G illumination. The photocurrent density is determined for NW diameters from100-250nm, period (spacing) from250-1000nm, and length of5m. The dependence of photocurrent density on NW bandgap is also determined. For each NW bandgap, the optimum diameter and period are determined to obtain current matching between the top NW cell and the bottom Si cell. This thesis explores a method which combined with electron beam lithography(EBL) and inductively coupled plasma(ICP) to fabricate GaAs NWs.Another focus of this thesis is nano-scale Fresnel lens. The reflectance, transmittance and absorptance of nano-scale Fresnel lens arrays are calculated by solving Maxwell’s equations using the finite element method. This Fresnel lens is used on Ⅲ-Ⅴ multi-junction solar cell. The influence of Fresnel lens on multi-junction solar cell has been investigated. A method which combines the electron beam lithography(EBL) and inductively coupled plasma(ICP) etching is developed to fabricate nano-scale Fresnel lens arrays on Spire Ⅲ-Ⅴ multi-junction solar cell. Finally, the Ⅰ-Ⅴ curve and the performance of this solar cell are measured.更多还原