Advantages and shortcomings of UMG silicon in photovoltaic device production

Published: May 1, 2010

By Rainer Krause, Manager of the ISC Technology Centre, IBM Corporation; Harold Hovel, Watson Research Laboratory, IBM Corporation; Eric Marshall, Watson Research Center, IBM Corporation; Gerd Pfeiffer, IBM Corporation; Zhengwen Li, Semiconductor Research and Development Center, IBM Corporation; Larry Clevenger, Senior Technical Staff Member, IBM Corporation; Kevin Petrarca, Watson Research Center, IBM Corporation; Davood Shahrjedi, Watson Research Center, IBM Corporation; Kevin Prettyman, Microelectronic Division, IBM Corporation; Steve Johnston, Research Scientist, Measurements & Characterization Division, NREL, Golden, Colorado, USA

Upgraded metallurgical-grade (UMG) silicon is a lower cost and lower quality form of solar-grade silicon that is capable of producing solar cells at over 16% efficiency. This paper presents some of the economic advantages and technical concerns and solutions associated with producing silicon based PV from UMG, as well as preliminary solar cell results using this material. Results are based on a comparison of cells made in a turnkey line (Schmid Group) using alloy blends of 10%, 20%, 30% and 100% UMG, mixed with solar-grade Si before ingot growth. Detailed characterization was carried out on these finished cells according to lifetime, LBIC, diffusion length and luminescence imaging to determine correlations of performance with basic parameters. Requirements for material cost and cell performance necessary for UMG solar cells to be cost competitive are also presented.

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