Nanophotonic structures have attracted attention for light trapping in solar cells with the potential to manage and direct light absorption on the nanoscale. While both randomly textured and ...nanophotonic structures have been investigated, the relationship between photocurrent and the spatial correlations of random or designed surfaces has been unclear. Here we systematically design pseudorandom arrays of nanostructures based on their power spectral density, and correlate the spatial frequencies with measured and simulated photocurrent. The integrated cell design consists of a patterned plasmonic back reflector and a nanostructured semiconductor top interface, which gives broadband and isotropic photocurrent enhancement.
We present a generic approach for the optimization of light-trapping patterns for thin-film solar cells. The optimization is based on tailoring the spatial frequencies in the light-trapping pattern ...to the waveguide modes supported by the thin-film solar cell stack. We calculate the dispersion relations for waveguide modes in thin-film Si solar cells and use them to define the required spatial frequency band for light trapping. We use a Monte Carlo algorithm to optimize the scattering power spectral density (PSD) of a random array of Mie scatterers on top of a-Si:H cells. The optimized particle array has a PSD that is larger in the desired spatial frequency range than the PSD of a random array and contains contributions at more spatial frequencies than the PSD of a periodic array. Three-dimensional finite-difference time-domain simulations on thin-film solar cells with different light-trapping patterns show that the optimized particle array results in more efficient light trapping than a random array of Mie scatterers. We use the same approach to design a random texture and compare this to the Asahi-U-type texture. We show that the optimized texture outperforms the Asahi-U pattern and an optimized periodic pattern. The light-trapping patterns presented avoid the ohmic absorption losses found in metallic (plasmonic) patterns. They can be tailored to specific spatial frequency ranges, do not contain materials that are incompatible with high-temperature processes, nor require patterning of the active layer. Therefore, they are applicable to nearly all types of thin-film solar cells.
Plasmonic nanostructures have been recently investigated as a possible way to improve absorption of light in solar cells. The strong interaction of small metal nanostructures with light allows ...control over the propagation of light at the nanoscale and thus the design of ultrathin solar cells in which light is trapped in the active layer and efficiently absorbed. In this paper we review some of our recent work in the field of plasmonics for improved solar cells. We have investigated two possible ways of integrating metal nanoparticles in a solar cell. First, a layer of Ag nanoparticles that improves the standard antireflection coating used for crystalline and amorphous silicon solar cells has been designed and fabricated. Second, regular and random arrays of metal nanostructures have been designed to couple light in waveguide modes of thin semiconductor layers. Using a large-scale, relative inexpensive nano-imprint technique, we have designed a back-contact light trapping surface for a-Si:H solar cells which show enhanced efficiency over standard randomly textured cells.
We experimentally compare the light trapping efficiency of dielectric and metallic backscattering patterns in thin-film a-Si:H solar cells. We compare devices with randomly patterned Ag back contacts ...that are covered with either flat or patterned aluminum-doped ZnO (AZO) buffer layers and find the nanostructure at the AZO/a-Si:H interface is key to achieve efficient light trapping. Simulations show that purely dielectric scattering patterns with flat Ag and a patterned AZO/a-Si:H interface can outperform geometries in which the Ag is also patterned. The scattering from the dielectric patterns is due to geometrical Mie resonances in the AZO nanostructures. The optimized dielectric geometries avoid parasitic Ohmic losses due to plasmon resonances in the Ag, and open the way to a large number of new light trapping designs based on purely dielectric resonant light scattering.
A series of (n–i–p) a‐Si:H solar cells with light‐trapping by front‐side plasmonic Ag nanoparticle arrays was compared to a reference without the plasmonic arrays as well as to a benchmark with a ...conventional textured back‐side reflector for light‐trapping. The external quantum efficiency of the solar cells was determined experimentally by spectral response measurements. The comparison gives a comprehensive snap‐shot of the potential of front‐side plasmonic light‐trapping in a‐Si:H solar cells for the array parameterization used in this study. Relative to the reference the plasmonic arrays lead to clearly enhanced light‐trapping in the longer wavelength range (600–800 nm). This enhancement is lower than the one achieved by the benchmark though, which is discussed in terms of further research perspectives.
The Apr 2010 release of the Department of Health and Human Services' (DHHS') Open Government strategy was a major step forward in expanding health data access. The DHHS developed the strategy in ...response to Pres Barack Obama's Open Government Directive--a call for federal agencies to create practical, public access to information they maintain internally. The Open Government strategy is an excellent step forward. If the initiative is to achieve its potential, the DHHS should follow a set of 3 principles in its ongoing and future efforts to make government data more valuable and accessible. These principles and their potential to harness the power of the government's data are evidenced in 2 ongoing efforts: the Community Health Data Initiative--part of the Open Government strategy--and a multipayer claims database project for comparative effectiveness research. Here, Conway and VanLare discuss the 3 principles and exemplary projects.
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