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Journal ArticleDOI

Strong broadband optical absorption in silicon nanowire films

01 Jan 2007-Journal of Nanophotonics (International Society for Optics and Photonics)-Vol. 1, Iss: 1, pp 013552
TL;DR: The broadband optical absorption properties of silicon nanowire (SiNW) films fabricated on glass substrates by wet etching and chemical vapor deposition (CVD) have been measured and found to be higher than solid thin films of equivalent thickness.
Abstract: The broadband optical absorption properties of silicon nanowire (SiNW) films fabricated on glass substrates by wet etching and chemical vapor deposition (CVD) have been measured and found to be higher than solid thin films of equivalent thickness. The observed behavior is adequately explained by light scattering and light trapping though some of the observed absorption is due to a high density of surface states in the nanowires films, as evidenced by the partial reduction in high residual sub-bandgap absorption after hydrogen passivation. Finite difference time domain simulations show strong resonance within and between the nanowires in a vertically oriented array and describe the experimental absorption data well. These structures may be of interest in optical films and optoelectronic device applications.
Citations
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Journal ArticleDOI
TL;DR: The observed absorption enhancement and collection efficiency enable a cell geometry that not only uses 1/100th the material of traditional wafer-based devices, but also may offer increased photovoltaic efficiency owing to an effective optical concentration of up to 20 times.
Abstract: The use of silicon nanostructures in solar cells offers a number of benefits, such as the fact they can be used on flexible substrates. A silicon wire-array structure, containing reflecting nanoparticles for enhanced absorption, is now shown to achieve 96% peak absorption efficiency, capturing 85% of light with only 1% of the silicon used in comparable commercial cells. Si wire arrays are a promising architecture for solar-energy-harvesting applications, and may offer a mechanically flexible alternative to Si wafers for photovoltaics1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17. To achieve competitive conversion efficiencies, the wires must absorb sunlight over a broad range of wavelengths and incidence angles, despite occupying only a modest fraction of the array’s volume. Here, we show that arrays having less than 5% areal fraction of wires can achieve up to 96% peak absorption, and that they can absorb up to 85% of day-integrated, above-bandgap direct sunlight. In fact, these arrays show enhanced near-infrared absorption, which allows their overall sunlight absorption to exceed the ray-optics light-trapping absorption limit18 for an equivalent volume of randomly textured planar Si, over a broad range of incidence angles. We furthermore demonstrate that the light absorbed by Si wire arrays can be collected with a peak external quantum efficiency of 0.89, and that they show broadband, near-unity internal quantum efficiency for carrier collection through a radial semiconductor/liquid junction at the surface of each wire. The observed absorption enhancement and collection efficiency enable a cell geometry that not only uses 1/100th the material of traditional wafer-based devices, but also may offer increased photovoltaic efficiency owing to an effective optical concentration of up to 20 times.

1,346 citations


Cites background from "Strong broadband optical absorption..."

  • ...A particular concern for photovoltaic applications of VLS-grown wire arrays is the possibility of parasitic absorption, which could be caused by the presence of surface states, impurities or residual VLS catalyst metal deposit...

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Journal ArticleDOI
TL;DR: In this paper, the optical reflectance of the silicon nanowire solar cells is reduced by one to two orders of magnitude compared to planar cells, and a promising current density of ∼1.6mA∕cm2 for 1.8cm2 cells was obtained, with a broad external quantum efficiency of ∼12% at 690nm.
Abstract: Silicon nanowire-based solar cells on metal foil are described. The key benefits of such devices are discussed, followed by optical reflectance, current-voltage, and external quantum efficiency data for a cell design employing a thin amorphous silicon layer deposited on the nanowire array to form the p-n junction. A promising current density of ∼1.6mA∕cm2 for 1.8cm2 cells was obtained, and a broad external quantum efficiency was measured with a maximum value of ∼12% at 690nm. The optical reflectance of the silicon nanowire solar cells is reduced by one to two orders of magnitude compared to planar cells.

997 citations

Journal ArticleDOI
TL;DR: In this article, a single core-shell p-i-n junction GaAs nanowire solar cell grown on a silicon substrate was shown to achieve a short-circuit current of 180 mA cm-2 at 1 sun illumination, more than one order of magnitude higher than that predicted from the Lambert-Beer law.
Abstract: 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.

756 citations

Journal ArticleDOI
TL;DR: The methods described herein comprise a valuable platform for measuring the properties of semiconductor nanowires, and are expected to be instrumental when designing an efficient macroscopic solar cell based on arrays of such nanostructures.
Abstract: Single-nanowire solar cells were created by forming rectifying junctions in electrically contacted vapor-liquid-solid-grown Si nanowires. The nanowires had diameters in the range of 200 nm to 1.5 microm. Dark and light current-voltage measurements were made under simulated Air Mass 1.5 global illumination. Photovoltaic spectral response measurements were also performed. Scanning photocurrent microscopy indicated that the Si nanowire devices had minority carrier diffusion lengths of approximately 2 microm. Assuming bulk-dominated recombination, this value corresponds to a minimum carrier lifetime of approximately 15 ns, or assuming surface-dominated recombination, to a maximum surface recombination velocity of approximately 1350 cm s(-1). The methods described herein comprise a valuable platform for measuring the properties of semiconductor nanowires, and are expected to be instrumental when designing an efficient macroscopic solar cell based on arrays of such nanostructures.

601 citations

Journal ArticleDOI
TL;DR: The recent developments in the utilization of SiNWs for PV applications, the relationship between SiNW-based PV device structure and performance, and the challenges to obtaining high-performance cost-effective solar cells are reviewed.
Abstract: Semiconductor nanowires are attracting intense interest as a promising material for solar energy conversion for the new-generation photovoltaic (PV) technology. In particular, silicon nanowires (SiNWs) are under active investigation for PV applications because they offer novel approaches for solar-to-electric energy conversion leading to high-efficiency devices via simple manufacturing. This article reviews the recent developments in the utilization of SiNWs for PV applications, the relationship between SiNW-based PV device structure and performance, and the challenges to obtaining high-performance cost-effective solar cells.

580 citations

References
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Book
01 Jan 1983
TL;DR: In this paper, a Potpourri of Particles is used to describe surface modes in small Particles and the Angular Dependence of Scattering is shown to be a function of the size of the particles.
Abstract: BASIC THEORY. Electromagnetic Theory. Absorption and Scattering by an Arbitrary Particle. Absorption and Scattering by a Sphere. Particles Small Compared with the Wavelength. Rayleigh--Gans Theory. Geometrical Optics. A Potpourri of Particles. OPTICAL PROPERTIES OF BULK MATTER. Classical Theories of Optical Constants. Measured Optical Properties. OPTICAL PROPERTIES OF PARTICLES. Extinction. Surface Modes in Small Particles. Angular Dependence of Scattering. A Miscellany of Applications. Appendices. References. Index.

16,859 citations

Journal ArticleDOI

6,579 citations


"Strong broadband optical absorption..." refers methods in this paper

  • ...Nanowires were synthesized using the vapor-liquid-solid (VLS) growth mechanism [19] in a...

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Journal ArticleDOI
17 Aug 2001-Science
TL;DR: The small size and capability of these semiconductor nanowires for sensitive, label-free, real-time detection of a wide range of chemical and biological species could be exploited in array-based screening and in vivo diagnostics.
Abstract: Boron-doped silicon nanowires (SiNWs) were used to create highly sensitive, real-time electrically based sensors for biological and chemical species. Amine- and oxide-functionalized SiNWs exhibit pH-dependent conductance that was linear over a large dynamic range and could be understood in terms of the change in surface charge during protonation and deprotonation. Biotin-modified SiNWs were used to detect streptavidin down to at least a picomolar concentration range. In addition, antigen-functionalized SiNWs show reversible antibody binding and concentration-dependent detection in real time. Lastly, detection of the reversible binding of the metabolic indicator Ca2+ was demonstrated. The small size and capability of these semiconductor nanowires for sensitive, label-free, real-time detection of a wide range of chemical and biological species could be exploited in array-based screening and in vivo diagnostics.

5,841 citations


"Strong broadband optical absorption..." refers background in this paper

  • ...High-mobility transistors [5], light emitting diodes [6], bio/chemical sensors [7], and other applications have been demonstrated primarily in the form of individual nanowire devices, though some devices based on arrays have been shown [8]....

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Journal ArticleDOI
Yi Cui1, Zhaohui Zhong1, Deli Wang1, Wayne U. Wang1, Charles M. Lieber1 
TL;DR: In this article, the influence of source-drain contact thermal annealing and surface passivation on key transistor properties was examined, and it was shown that thermal annaling and passivation of oxide defects using chemical modification can increase the average transconductance from 45 to 800 nS and average mobility from 30 to 560 cm 2 /V
Abstract: Silicon nanowires can be prepared with single-crystal structures, diameters as small as several nanometers and controllable hole and electron doping, and thus represent powerful building blocks for nanoelectronics devices such as field effect transistors. To explore the potential limits of silicon nanowire transistors, we have examined the influence of source-drain contact thermal annealing and surface passivation on key transistor properties. Thermal annealing and passivation of oxide defects using chemical modification were found to increase the average transconductance from 45 to 800 nS and average mobility from 30 to 560 cm 2 /V‚s with peak values of 2000 nS and 1350 cm 2 /V‚s, respectively. The comparison of these results and other key parameters with state-of-the-art planar silicon devices shows substantial advantages for silicon nanowires. The uses of nanowires as building blocks for future nanoelectronics are discussed.

2,157 citations


"Strong broadband optical absorption..." refers background in this paper

  • ...High-mobility transistors [5], light emitting diodes [6], bio/chemical sensors [7], and other applications have been demonstrated primarily in the form of individual nanowire devices, though some devices based on arrays have been shown [8]....

    [...]

Journal ArticleDOI
TL;DR: Optical thin-film materials with low refractive index for broadband elimination of Fresnel reflection were used in this paper, where the authors proposed a method to eliminate the reflection in optical thin-films.
Abstract: Optical thin-film materials with low refractive index for broadband elimination of Fresnel reflection

1,153 citations


"Strong broadband optical absorption..." refers result in this paper

  • ...the same wavelength range our samples typically show a constant total reflectance of ≤ 2% and a specular reflectance of < 1% (not shown), on par with recent data presented by Shubert and co-workers for graded index nanostructured films [21]....

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