Broadband optical absorption enhancement through coherent light trapping in thin-film photovoltaic cells

Electrical Engineering, Stanford University, Stanford, CA 94305, USA.
Optics Express (Impact Factor: 3.49). 05/2008; 16(8):5385-96. DOI: 10.1364/OE.16.005385
Source: PubMed


We show that optical absorption in thin-film photovoltaic cells can be enhanced by inserting a tuned two-component aperiodic dielectric stack into the device structure. These coatings are a generalization and unification of the concepts of an anti-reflection coating used in solar cells and high-reflectivity distributed Bragg mirror used in resonant cavity-enhanced narrowband photodetectors. Optimized two-component coatings approach the physically realizable limit and optimally redistribute the spectral photon density-of-states to enhance the absorption of the active layer across its absorption spectrum. Specific designs for thin-film organic solar cells increase the photocurrent under AM1.5 illumination, averaged over all incident angles and polarizations, by up to 40%.

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Available from: Peter Peumans, May 06, 2014
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    • "Thin film solar cell can reduce the cost of raw material and be assembled on flexible substrate, thus has attracted significant research interest recently [1] [2] [3] [4] [5]. However, due to the extremely small thickness (hundreds of nanometers in general) of these films, the radiation absorption is quite small, which strongly limits the energy conversion efficiency [1]. To achieve high absorption in thin film, many photon management schemes have been proposed to enhance light trapping in the thin film, such as photonic crystal [2], plasmonics [3] [4], grating [5] [6] [7], random textured surface [8], nanowires or nanoholes [9–11 ], etc. Theoretical investigations showed that for structures with features size comparable to the wavelength, the radiation absorption enhancement can exceed the conventional Yablonovitch 4n 2 limit [12]. "
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    ABSTRACT: The radiation absorption in thin films with three disordered nanohole patterns, i.e., random position, non-uniform radius, and amorphous pattern, are numerically investigated by finite-difference time-domain (FDTD) simulations. Disorder can alter the absorption spectra and has an impact on the broadband absorption performance. Compared to random position and non-uniform radius nanoholes, amorphous pattern can induce a much better integrated absorption. The power density spectra indicate that amorphous pattern nanoholes reduce the symmetry and provide more resonance modes that are desired for the broadband absorption. The application condition for amorphous pattern nanoholes shows that they are much more appropriate in absorption enhancement for weak absorption materials. Amorphous silicon thin films with disordered nanohole patterns are applied in solar radiation absorbers. Four configurations of thin films with different nanohole patterns show that interference between layers in absorbers will change the absorption performance. Therefore, it is necessary to optimize the whole radiation absorbers although single thin film with amorphous pattern nanohole has reached optimal absorption.
    Full-text · Article · Jan 2015 · Journal of Quantitative Spectroscopy and Radiative Transfer
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    • "A 40% broad-band photo-current enhancement for a thin-film photovoltaic cell as been reported [6]. It was obtained by modifying the photon density of state by using specifically designed dielectric mirrors. "
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    ABSTRACT: Light trapping enhancement is a major research field in photovoltaics. Scarce and expensive resources for semiconductor material drive the research on light management in thin absorber layer. This paper reviews some of the known techniques, from back reflector to nanophotonic technologies such as nanowires or plasmonic-enhanced photovoltaic devices. Light trapping enhancement can reach similar to 100 fold and experimental demonstrations of device exceeding the ray optics limits have been reported.
    Full-text · Article · Feb 2014 · Proceedings of SPIE - The International Society for Optical Engineering
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    • "They demonstrate than a lambertian reflector of ideal reflection coefficient localized at the bottom of the absorber layer leads to a path length enhancement of 4n², n being the refractive index of the absorber material. A 40% broad-band photo-current enhancement for a thin-film photovoltaic cell as been reported [6]. It was obtained by modifying the photon density of state by using specifically designed dielectric mirrors. "

    Full-text · Article · May 2013
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