ZnO Nanorods as Antireflective Coatings for Industrial-Scale Single-Crystalline Silicon Solar Cells

In this work, both planar and textured, industrial scale (156mmx156mm) single-crystalline silicon (Si) solar cells have been fabricated using zinc oxide (ZnO) nanorods as antireflection coating (ARC). ZnO nanorods were grown in a few minutes via hydrothermal method within a commercially available microwave oven. Relative improvement in excess of 65% in the reflectivity was observed for both planar and textured Si surfaces. Through ZnO nanorods, effective lifetime (eff) measurements were presented to investigate the surface passivation property of such an ARC layer. ZnO nanorods increased the eff from 9 to 71s at a carrier injection level of 1015cm3. Increased carrier lifetime revealed the passivation effect of the ZnO nanorods in addition to their ARC property. 33% and 16% enhancement in the photovoltaic conversion efficiency was obtained in planar and textured single-crystalline solar cells, respectively. Our results reveal the potential of ZnO nanorods as ARC that can be deposited through simple solution-based methods and the method investigated herein can be simply adapted to industrial scale fabrication

Application of Si Nanowires Fabricated by Metal-Assisted Etching to Crystalline Si Solar Cells

Reflection and transmission through a solar cell can be significantly reduced using light-trapping structures. This approach can be applied to both crystalline and thin-film solar cells to improve the light absorption and conversion efficiency of the cell. In this study, vertically aligned Si nanowires were fabricated over a large area via a metal-assisted etching technique. Following a detailed parametric study, nanowires were applied to industrial-size (156 mm x 156 mm) Si solar cells. The reflectivity from the device surface was reduced to less than 5% for the entire visible spectrum (350-750 nm), including the blue-violet region. Standard solar cell fabrication procedures were employed to fabricate cells with and without Si nanowires, and the results showed that the efficiencies of solar cells with nanowires were similar to those of standard pyramid-textured cells, revealing the potential of the proposed concept. A systematic study of the dependence of the solar cell parameters on the length of the nanowires was performed. The quantum efficiency of the cells exhibited relatively poor performance in the blue-ultraviolet range of the spectrum, and enhancement in carrier generation was observed in the red-infrared region especially for shorter nanowires

Light management on industrial size c-Si solar cells by Si nanowires fabricated by metal-assisted etching

Absorption of the light by a solar cell can be improved significantly by light trapping structures formed on the front surface of the device. In particular, thin crystalline and amorphous solar cells are expected to benefit from the improved light absorption in a region closer to the surface of the cell. Recently, we have shown that vertically aligned silicon (Si) nanowires formed on flat (100) Si wafer surface by metal assisted etching can effectively be used for this purpose. In this paper we present demonstration of nanowire application to industrial size solar cell system and a comparison between flat and pyramid textured Si wafers. Standard procedures were followed to fabricate solar cells with and without Si nanowire process on mirror like and pyramid textured Si wafers. The dependence of the solar cell parameters on the process parameters was studied systematically. Reflection spectra showed successful light trapping behavior on the surface of the cells. In all samples, we have obtained excellent current-voltage (I-V) characteristics with high fill factors. However, the efficiency of the cells was found to decrease with the etch duration. This can be attributed to the increased recombination along the nanowires or increased surface area due to the roughening of the surface after etching process