Department of Chemistry, University of California, Berkeley, California 94720, USA.
Nano Lett. 2010 Mar 10;10(3):1082-7. doi: 10.1021/nl100161z.
Thin-film structures can reduce the cost of solar power by using inexpensive substrates and a lower quantity and quality of semiconductor material. However, the resulting short optical path length and minority carrier diffusion length necessitates either a high absorption coefficient or excellent light trapping. Semiconducting nanowire arrays have already been shown to have low reflective losses compared to planar semiconductors, but their light-trapping properties have not been measured. Using optical transmission and photocurrent measurements on thin silicon films, we demonstrate that ordered arrays of silicon nanowires increase the path length of incident solar radiation by up to a factor of 73. This extraordinary light-trapping path length enhancement factor is above the randomized scattering (Lambertian) limit (2n(2) approximately 25 without a back reflector) and is superior to other light-trapping methods. By changing the silicon film thickness and nanowire length, we show that there is a competition between improved absorption and increased surface recombination; for nanowire arrays fabricated from 8 mum thick silicon films, the enhanced absorption can dominate over surface recombination, even without any surface passivation. These nanowire devices give efficiencies above 5%, with short-circuit photocurrents higher than planar control samples.
薄膜结构可以通过使用廉价的衬底和较少数量及质量的半导体材料来降低太阳能的成本。然而，由此产生的短光程和少数载流子扩散长度需要高吸收系数或优异的光捕获。已经证明，与平面半导体相比，半导体纳米线阵列具有较低的反射损耗，但它们的光捕获特性尚未测量。通过对薄硅膜进行光学传输和光电流测量，我们证明有序的硅纳米线阵列将入射太阳辐射的光程延长了多达 73 倍。这种非凡的光捕获光程增强因子超过了随机散射（朗伯）极限（无后反射器时为 2n(2)约 25），优于其他光捕获方法。通过改变硅膜的厚度和纳米线的长度，我们表明在改善吸收和增加表面复合之间存在竞争；对于由 8 微米厚的硅膜制成的纳米线阵列，即使没有任何表面钝化，增强的吸收也可以超过表面复合。这些纳米线器件的效率超过 5%，短路光电流高于平面对照样品。
