Optimal Design of a CIGS Module Grid
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f a CIGS Module Grid Yiyang Li, Shihang Yang, Xieqiu Zhang and Xudong Xiao MRS Proceedings / Volume 1315 / 2011 DOI: 10.1557/opl.2011.1393
Link to this article: http://journals.cambridge.org/abstract_S1946427411013935 How to cite this article: Yiyang Li, Shihang Yang, Xieqiu Zhang and Xudong Xiao (2011). Optimal Design of a CIGS Module Grid. MRS Proceedings,1315, mrsf101315mm1104 doi:10.1557/ opl.2011.1393 Request Permissions : Click here
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Mater. Res. Soc. Symp. Proc. Vol. 1315 © 2011 Materials Research Society DOI: 10.1557/opl.2011.1393
Optimal Design of a CIGS Module Grid Yiyang Li1, Shihang Yang2, Xieqiu Zhang2, Xudong Xiao2 1 Franklin W. Olin College of Engineering, Needham, MA, 02492, USA 2 Chinese University of Hong Kong, Sha Tin, N.T., Hong Kong ABSTRACT Solar cells based on Cu(In, Ga)Se2 (CIGS) have made significant strides in the past decades with a record efficiency of over 20% [1]. A problem with CIGS modules is the high resistive losses along the transparent top contact. One solution is to deposit highly-conductive metal grids to collect the current. We use finite-element analysis to determine the effectiveness of the metal grid under a variety of parameters. We identify the resistance of the top contact and the width of the scribes as the most important factors in determining whether a metal grid would present a significant efficiency gain. Using the same model, we also investigate methods to optimize the design of the grid. INTRODUCTION Solar cells based on Cu(In, Ga)Se2 (CIGS) have been significantly improved in the past decade with a record efficiency of 20.3%[1]. However, small cells, on the order of 0.5 cm2 are impractical for commercial applications. Small modules on the order of 10-100 cm2 can be used to develop technologies that can be scaled up to full production modules [2]. One such technology is the deposition of a nontransparent but highly conductive metal grid to collect current. These grids have been shown to reduce resistive losses from the lowconductivity transparent top contact ZnO:Al, as well as reduce long-term effects of degradation [3]. However, these grids increase dead area resulting in a lower overall current. We aim to determine the conditions where the metal grid provides a significant increase in the efficiency of the solar cell. We use finite-element analysis solving Ohm's Law combined with a one-diode model of a solar cell to simulate the electrostatics of a CIGS module. Using this model, we vary parameters to determine their effects on solar cell performance. MODEL AND METHODS Mini-modules of around 100 cm2 resemble production modules because they consist of a number of equally-spaced slices connected in series (figure 1). Many structural parameters such as slice widths, scribing, encapsulation, front and back contacts are similar, making them excellent platforms to develop larger production modules [2] CIGS Slice Design Figure 1(a) shows 100x100 mm mini-modules divided into
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