Aligned single-crystalline Si nanowire arrays for photovoltaic applications
Aligned single-crystalline Si nanowire arrays for photovoltaic applications
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DOI：
10.1002/smll.200500137
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发表时间：
2005-11-01
期刊：
影响因子：
13.3
通讯作者：
Zhu, J
中科院分区：
文献类型：
--
作者：
Peng, KQ;Xu, Y;Zhu, J
图1. a）硅纳米线阵列的SEM横截面图像。B）由p型（111）取向的硅衬底制备的单个SiNW的TEM图像。c）图1b中纳米线的HRTEM图像（插图是沿沿着1/2 110轴记录的艾德图案）。d）由p型（100）取向的硅衬底合成的纳米线的HRTEM图像（插图是沿沿着001 1/2轴记录的其艾德图案）。e、f）由多晶Si衬底制备的SiNW阵列的SEM图像。Small 2005，1，No.11，1062-1067 2005 Wiley-VCH Verlag GmbH & Co. KGaA，D-69451魏因海姆www.小日记com 1063 tion.我们详细的TEM研究已经证实，所获得的硅纳米线的取向总是与初始Si衬底的取向相同。这些结果表明，具有理想的轴向晶体取向的硅纳米线可以通过选择具有相同取向的初始硅衬底来完全控制。与其他蚀刻方法不同，本蚀刻技术显示出对Si衬底的晶体学取向和掺杂特性的依赖性很小。因此，这种刻蚀方法可以很容易地扩展到多晶Si衬底上，并且还在多晶Si衬底上成功制备了大面积独立SiNW阵列。图1 e和f示出了在多晶Si衬底上制备的大面积SiNW阵列的SEM图像。可以看出，蚀刻的多晶硅表面由许多由SiNW束组成的结构域构成;这些域由明显的边界分开。这些域的典型尺寸等于单个Si微晶的尺寸。显然，这些畴界是Si微晶的边界。降低光损耗是获得高效率硅太阳电池的重要因素之一。为了实现这一目标，太阳能电池的顶面通常被纹理化[10]或覆盖有抗反射涂层（ARC）。[11]各向异性碱性绒面化是单晶硅的标准工艺，广泛应用于当前太阳能电池生产中。然而，对于多晶Si，这种方法并不有效，因为只有一小部分晶粒具有100 1/2晶体取向。多孔硅在400-1000 nm波长范围内的反射率可降低到5.8%，可以替代其它表面织构结构和反射涂层。[12]目前，具有多孔结构作为ARC的太阳能电池的效率约为7- 12%。我们合成的样品的黑色意味着它们可能具有优异的光学性能。因此，大面积硅纳米线阵列的反射行为进行了研究，鉴于其潜在的光伏应用作为一个反射表面。图2显示了
Figure 1. a) SEM cross-section image of silicon nanowire arrays. b) TEM image of an individual SiNW prepared from a p-type (111)-oriented silicon substrate. c) HRTEM image of the nanowire in Figure 1b (the inset is the ED pattern recorded along the ½110 axis). d) HRTEM image of a nanowire synthesized from a ptype (100)-oriented silicon substrate (the inset is its ED pattern recorded along the 001 ½ axis). e, f) SEM images of SiNW arrays prepared from a polycrystalline Si substrate. small 2005, 1, No. 11, 1062–1067 2005 Wiley-VCH Verlag GmbH & Co. KGaA, D-69451 Weinheim www. small-journal. com 1063 tion. Our detailed TEM investigation has confirmed that the orientations of obtained silicon nanowires are always identical with the orientation of initial Si substrates. These results indicate that SiNWs with desirable axial crystallographic orientations could be fully controlled by selecting initial Si substrates with identical orientations. Unlike other etching methods, the present etching technique shows little dependence upon the crystallographic orientation and doping characteristics of Si substrates. Therefore, this etching method can be readily extended to polycrystalline Si substrates.Large-area freestanding SiNWs arrays have also been successfully prepared on polycrystalline Si substrates. Figure 1e and f show SEM images of large-area SiNW arrays prepared on polycrystalline Si substrates. It can be seen that the etched polycrystalline Si surface is built up of many structural domains composed of bundles of SiNWs; these domains are separated by obvious boundaries. The typical size of these domains was equal to the size of a single Si crystallite. Evidently, these domain boundaries are the boundaries of the Si crystallites. The reduction of optical loss is one of the important factors in obtaining high-efficiency Si solar cells. To achieve this goal, the top surface of the solar cells is generally texturized [10] or covered with an antireflection coating (ARC).[11] Anisotropic alkaline texturization is a standard process for monocrystalline Si and is widely applied in present solar cell production. However, for polycrystalline Si, this method is not effective because only a fraction of the grains have the 100 ½ crystallographic orientation. It is well known that porous silicon (PSi) can reduce the reflectance to% 5.8% in the 400–1000 nm wavelength range and therefore can replace other surface-textured microstructure and antireflection coatings.[12] The present efficiency of solar cells with a porous structure as the ARC is about 7–12%. The black color of our as-synthesized samples implies their possible excellent optical antireflection property. Therefore, reflectance behavior of the large-area SiNW arrays was studied in view of its potential photovoltaic application as an antireflection surface. Figure2 shows the