Advanced Optical Modeling of Thin-film Silicon Solar Cells with 1-D Periodic Gratings.
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Advanced Optical Modeling of Thin-film Silicon Solar Cells with 1-D Periodic Gratings. S. Solntsev1, O. Isabella1, D. Caratelli2, M. Kyriakou1, O. Yarovyi2, and M. Zeman1 1 2
Delft University of Technology – PVMD/DIMES, P.O. Box 5053, 2628 CD Delft, Netherlands Delft University of Technology – IRCTR, P.O. Box 5031, 2600 GA Delft, Netherlands
ABSTRACT Design of one-dimensional periodic gratings is investigated for enhancing the light absorption in thin-film silicon solar cells due to scattering at rough interfaces that are introduced into solar cells by the gratings. A rigorous full-wave analysis is carried out in order to determine the optical properties of amorphous and microcrystalline silicon solar cells in PIN and NIP configurations, respectively. Optimal geometrical parameters of 1-D gratings for maximizing photocurrent density in thin-film silicon solar cells are determined. INTRODUCTION In thin-film silicon solar cells (TFSC) an efficient light trapping is needed in order to maximize the absorption in the absorber layer and consequently increase the energy conversion efficiency. One-dimensional (1-D) periodic gratings represent an alternative solution [1] to randomly surface-textured morphologies of solar cell carriers, since they can efficiently scatter light into large discrete angles resulting in an increase of the optical path length inside the absorber layer. The control of the geometrical parameters of gratings such as shape, period (P), height (h), and duty cycle (dC) enables us to enhance light scattering over a broad wavelength range. Periodically textured sub-micron gratings can be fabricated by using, for example, the technology for CD/DVD manufacturing. The optical modeling of today’s TFSC is not a trivial task because of their complex 3-D geometry, consisting of layers with thicknesses spanning over several orders of magnitude (from nm up to several μm) and interface roughness related to the textured substrate carrier. In order to determine the light intensity distribution in such devices it is necessary to solve Maxwell equations numerically. This approach has been recently used to predict the photocurrent density enhancement in TFSC, but either the analysis was focused on the absorber material only [2][3], or carried out with solvers based on Finite Element Method (FEM) [4][5]. In the presented study the full-wave analysis of complete solar cell structures has been performed by using the finitedifference time-domain (FDTD) method [6]. The freely available software package MEEP [7] has been used in the development of the FDTD-based modeling tool to perform the optical simulations of single-junction TFSC formed by realistic dispersive materials on a substrate with 1-D periodic sub-micrometer gratings. SIMULATIONS Fitting of optical properties of the layers In order to correctly evaluate the electromagnetic field in the structure and calculate the absorption inside each layer of TFSC, a challenge was to obtain an accurate matching of the
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electronic properties of the materials of the layers
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