Strong Geometrical Dependence of the Absorption of Light in Arrays of Semiconductor Nanowires

Diedenhofen, Silke L.; Janssen, O.T.A.; Grzela, Grzegorz; Bakkers, Erik P. A. M.; Rivas, Jaime Gómez

doi:10.1021/nn103596n

Cited by 178 publications

(180 citation statements)

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“…Interestingly, when these arrays stand on a Lambertian back-reflector, an asymptotic increase in light trapping for low filling factors (FFs) is predicted 19 . This is advantageous for improvement of the efficiency-to-cost ratio of solar cells and has led to the demonstration of microwire arrays exhibiting higher absorption than in the equivalent thickness of textured film 19,21,22 . The case for nanowires is quite different.…”

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“…This leads to an apparent solar conversion efficiency of 40%. The second device shows a short-circuit current of 173 mA cm 22 and an apparent efficiency of 28%. The reason for these very high efficiencies is the mismatch between the absorption cross-section and the physical bounds of the nanowires, hinting at a very large absorption crosssection.…”

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“…Under illumination, the diode curve is shifted downwards as a consequence of photogeneration and separation of electron-hole pairs, giving a short-circuit current of 256 pA. The diameter of the nanowire is 425 nm, corresponding to an apparent photogenerated current density of 180 mA cm 22 . The open-circuit voltage V OC and FF are 0.43 V and 0.52, respectively, both of which should be improved by optimizing the resistivity, the thickness of the doped layers and surface passivation 29 .…”

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“…The open-circuit voltage V OC and FF are 0.43 V and 0.52, respectively, both of which should be improved by optimizing the resistivity, the thickness of the doped layers and surface passivation 29 . The generated power at the maximum power point is 57 pW, corresponding to 40 mW cm 22 . Dividing the generated power density by the incident power density, the solar cell yields an apparent efficiency of 40%.…”

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“…In Table 1 we list the best values for leading technologies such as single-junction crystalline silicon (c-Si) and GaAs, as well as triple-junction devices. The highest efficiency is provided by the triple-junction solar cell (34.1%), with a shortcircuit current of 14.7 mA cm 22 . In this case the short-circuit current is kept relatively low as it has to be matched between the three cells connected in series, and it is the high efficiency that generates the increase in V OC .…”

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Single-nanowire solar cells beyond the Shockley–Queisser limit

Jørgensen²,

et al. 2013

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Light management is of great importance in photovoltaic cells, as it determines the fraction of incident light entering the device. An optimal p-n junction combined with optimal light absorption can lead to a solar cell efficiency above the Shockley-Queisser limit. Here, we show how this is possible by studying photocurrent generation for a single core-shell p-i-n junction GaAs nanowire solar cell grown on a silicon substrate. At 1 sun illumination, a short-circuit current of 180 mA cm -2 is obtained, which is more than one order of magnitude higher than that predicted from the Lambert-Beer law. The enhanced light absorption is shown to be due to a light-concentrating property of the standing nanowire, as shown by photocurrent maps of the device. The results imply new limits for the maximum efficiency obtainable with III-V based nanowire solar cells under 1 sun illumination.N anowire-based solar cells hold great promise for third-generation photovoltaics and for powering nanoscale devices 1,2 . With the advent of third-generation photovoltaics, solar cells will become cheaper and more efficient than current devices. In particular, a cost reduction may be achieved by reducing material use through the fabrication of nanowire arrays and radial p-n junctions [3][4][5] . The geometry of nanowire crystals is expected to favour elastic strain relaxation, providing great freedom in the design of new compositional multijunction solar cells 6 grown on mismatched materials 7,8 . The efficiencies of nanostructured solar cells have increased over time and have now reached up to 13.8%, due to improvements in materials and new device concepts [9][10][11][12][13][14] .Light absorption in standing nanowires is a complex phenomenon, with a strong dependence on nanowire dimensions and the absorption coefficient of the raw materials [15][16][17][18] . In low-absorbing microwire arrays, such as those composed of silicon, light absorption is understood via ray optics or by calculation of the integrated local density of optical states of the nanowire film 19,20 . Interestingly, when these arrays stand on a Lambertian back-reflector, an asymptotic increase in light trapping for low filling factors (FFs) is predicted 19 . This is advantageous for improvement of the efficiency-to-cost ratio of solar cells and has led to the demonstration of microwire arrays exhibiting higher absorption than in the equivalent thickness of textured film 19,21,22 . The case for nanowires is quite different. Nanowire diameters are smaller than or comparable to the radiation wavelength. In this case, optical interference and guiding effects play a dominant role in relation to reflectivity and absorption spectra. For low-absorbing materials (for example, indirect bandgap materials such as silicon), waveguiding effects plays a key role 23,24 , whereas highly absorbing semiconductors (such as direct-bandgap GaAs) exhibit resonances that increase the total absorption several times. Nanowires lying on a substrate also exhibit such resonances, often described by Mi...

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