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PUBLISHED ONLINE: 18 MAY 2015 | http://www.nature.com/doifinder/10.1038/nnano.2015.89
Web End =DOI: 10.1038/NNANO.2015.89
The nanostructuring of silicon surfacesknown as black siliconis a promising approach to eliminate front-surface reection in photovoltaic devices without the need for a conventional antireection coating. This might lead to both an increase in efciency and a reduction in the manufacturing costs of solar cells. However, all previous attempts to integrate black silicon into solar cells have resulted in cell efciencies well below 20% due to the increased charge carrier recombination at the nanostructured surface. Here, we show that a conformal alumina lm can solve the issue of surface recombination in black silicon solar cells by providing excellent chemical and electrical passivation. We demonstrate that efciencies above 22% can be reached, even in thick interdigitated back-contacted cells, where carrier transport is very sensitive to front surface passivation. This means that the surface recombination issue has truly been solved and black silicon solar cells have real potential for industrial production. Furthermore, we show that the use of black silicon can result in a 3% increase in daily energy production when compared with a reference cell with the same efciency, due to its better angular acceptance.
Black silicon (b-Si)as its name impliesabsorbs light very efciently for a wide range of wavelengths and, as a result, appears black to the naked eye. Its high absorption is based on gradual
matching of the refractive index at the silicon/air interface using small nanostructures with dimensions below the wavelength of the incident light1. Various shapes (including nanocones2, nano-wires3, microwires4 and porous silicon5) have been used to achieve excellent light management effects. Because of its many superior properties, b-Si has potential for a range of applications, such as self-cleaning surfaces6, microelectromechanical systems7, ion mobility spectrometers8, terahertz emitters9, drug analysis10, photodetectors11 and antibacterial surfaces12.
Black silicon would also appear to be an ideal material for photo-voltaics due to its outstanding light management properties under the solar spectrum. In addition to boosting efciency, b-Si can provide signicant savings in manufacturing costs as there is no need to deposit a separate antireection coating. The main challenges that have hindered the use of b-Si in photovoltaics are related to increased surface recombination due to the larger surface area of the nanostructures, and the situation...