About the origin of low wafer performance and crystal defect generation on seed-cast growth of industrial mono-like silicon ingots

• Published in: Progress in photovoltaics 2014-08, Vol.22 (8), p.923-932
• Main Authors: Guerrero, Ismael, Parra, Vicente, Carballo, Teresa, Black, Andrés, Miranda, Miguel, Cancillo, David, Moralejo, Benito, Jiménez, Juan, Lelièvre, Jean-François, del Cañizo, Carlos
• Format: Article
• Language: English
• Subjects: Applied sciences; casting; Crystal defects; dislocation; Energy; Exact sciences and technology; Ingot casting; Ingots; LBIC; Markets; mono-like; Natural energy; photoluminescence; Photovoltaic cells; Photovoltaic conversion; Product innovation; silicon wafer; Solar cells; Solar cells. Photoelectrochemical cells; Solar energy; Wafers
• ISSN: 1062-7995; 1099-159X
• DOI: 10.1002/pip.2344

ABSTRACT The era of the seed‐cast grown monocrystalline‐based silicon ingots is coming. Mono‐like, pseudomono or quasimono wafers are product labels that can be nowadays found in the market, as a critical innovation for the photovoltaic industry. They integrate some of the most favorable features of the conventional silicon substrates for solar cells, so far, such as the high solar cell efficiency offered by the monocrystalline Czochralski‐Si (Cz‐Si) wafers and the lower cost, high productivity and full square‐shape that characterize the well‐known multicrystalline casting growth method. Nevertheless, this innovative crystal growth approach still faces a number of mass scale problems that need to be resolved, in order to gain a deep, 100% reliable and worldwide market: (i) extended defects formation during the growth process; (ii) optimization of the seed recycling; and (iii) parts of the ingots giving low solar cells performance, which directly affect the production costs and yield of this approach. Therefore, this paper presents a series of casting crystal growth experiments and characterization studies from ingots, wafers and cells manufactured in an industrial approach, showing the main sources of crystal defect formation, impurity enrichment and potential consequences at solar cell level. The previously mentioned technological drawbacks are directly addressed, proposing industrial actions to pave the way of this new wafer technology to high efficiency solar cells. Copyright © 2012 John Wiley & Sons, Ltd. The innovative seed‐cast growth process can entail a turning point for the affected and fluctuating photovoltaic market. However, this approach still needs to be reviewed before moving to mass scale activities in a stable manner. In this paper, sources of defect generation, low performance ingot regions and the reutilization of the original seed (cost reduction) are discussed from the results of several industrial scale experiments using casting furnace stations. Some strategies to improve the process quality are also proposed.