Efficient light trapping in a fluorescence solar collector by 3D photonic crystal

Abstract

Fluorescence collectors [1,2] provide efficient concentration and spectral dispersion of solar light for the conversion in multispectral solar cells such as tandem or triple cells [3,4] that allow reduction of cost and increase in efficiency [5][6][7]. One of the principle drawbacks of fluorescence collectors (flucos) consist in the loss of photons through the escape cone resulting from the lack of total reflection due to the contrast in refractive indices of fluco and its environment. This loss can be reduced by overcoating the illuminated (entrance) side with an angularly selective filter. Such selective filters prevent at least some luminescence photons in any type of absorber, e.g. fluco or semiconductor from escaping through the collector front side [8] and thus increase the internal photon density.By sufficient absorption and reemission in the fluco this higher flux is redistributed isotropically in the solid angle 4π and leads to a higher photoexcited state in the fluco which is attributed to an increase in chemical potential of the photon field [9]. This redistribution into 4π, analogously with the original isotropic emission, rises the photon flux towards the fluco edges as well where usually solar cells are attached [1,7] which benefit from the rise by a higher chemical potential of the electron-hole ensem-ble, equivalent with larger separation of quasi-Fermi levels [10][11][12], however the non-negligible reflection of the opal at λ ≤ 600 nm [13] may overcompensate the beneficial effect.We have performed spectral and angle dependent analyses of light emission from the illuminated fluorescence collector with and without selective filter at the light entrance side. We observe distinct differences in the spectral and angle dependent transmission and reflection spectra associated with the effect of the selective filter. Figure 1 (online colour at: www.pss-rapid.com) Spectral absorption and emission of a rodamine 6G doped fluorescence collector at normal incidence.The escape of photons from a fluorescence collector is substantially reduced by the addition of a 3D photonic crystal which is geometrically designed for the emission wavelengths of the collector. We analyze angle dependent spectral transmission and reflection of the opal and prove the blocking effect by recording the angle dependence of the spectral fluorescence from the collector with and without the opal. By comparison of both photon fluxes a reduction of the emission in the appropriate ranges of wavelength and angle by a factor > 10 is observed. For photovoltaic applications an increase in the internal photon density of the collector and likewise in the fluorescence photon flux fed to a solar cell can be expected, which might be overcompensated by the non-negligible reflection of the opal.

Photon Frequency Management Materials for Efficient Solar Energy Collection

“…Simulations carried out by Goldschmidt and co-workers 66,67 have shown 20% increases in efficiency with band edge lters. An increase in edge emission with the use of photonic opal crystals was also reported by Knabe et al 68 Debije et al 69,70 observed up to 12% more light collected on the edge of the collector by using Recently researchers have started attempting to improve photon collection efficiency by restricting the molecular orientation of the dye inside the collector. For example, a planar aligned dye with its absorbing axis parallel to the edge of collection will have an increased light output and a respective reduction edge light output in a direction perpendicular to the absorption axis.…”

Optical characterization of 3D photonic structures for light trapping in crystalline silicon solar cells

“…The first approach is used to enhance the absorption of photons with photon energy below the band gap so that the absorption coefficient for these photons is not so low, the second one to reduce for example the reemission through the escape cone in a fluorescence solar collector [2]. There are different methods to achieve light trapping: From a simple Bragg filter up to 3d photonic crystals which have several stop gaps or even a complete band gap.…”

Angular shaping of fluorescence from synthetic opal-based photonic crystal

“…Modification and enhancement of the fluorescence in photonic structures is important for development of optical sensors [ 1 ] and improvement of the fluorescence efficiency [ 2 ] and light harvesting ability in solar cells [ 3 ]. Most papers (see, for example, reviews [ 1 , 4 ]) deal with experimental and theoretical aspects of the fluorophores embedded in the multilayered films forming one-dimensional (1D) photonic crystals.…”

“…Photonic stop zones in 3D structures have been already proved useful for blocking undesirable light emission [ 9 ]. In particular, this effect was used to avoid leakage of light from the dye-sensitized solar cells [ 3 ], to suppress the radiative channels [ 10 ], and in such a way to improve the Förster resonance energy transfer between the dye molecules situated inside the photonic structure [ 11 ].…”