The emergence of n-type silicon for industrial solar cells

Assoc Professor Daniel Macdonald (Research School of Engineering)

SOLAR SEMINAR SERIES

DATE: 2012-12-04
TIME: 15:00:00 - 16:00:00
LOCATION: Ian Ross Seminar Room
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ABSTRACT:
The great majority of solar cells manufactured today are based on p-type silicon wafers. However, the most efficient modules on the market, produced by SunPower and Sanyo, are both made with n-type silicon wafers. Their market share remains small however, because these solar cells require elaborate fabrication processes, and are therefore more expensive in terms of $/Wpeak, despite their higher efficiency. The primary reason for the higher efficiency achieved with n-type silicon is the higher carrier lifetime in this material, due to the absence of boron-oxygen defects. However, there are also disadvantages in using n-type silicon, such as greater resistivity variations in the silicon ingots, and the need to use an alternative to the standard phosphorus diffusions that work so reliably for forming the p-n junction on p-type cells. These technical barriers have, in the past, deterred industry from developing low-cost n-type cells. Nevertheless, it is now clear that there are viable solutions to these problems, which has led to a recent resurgence of interest in these devices. This paper will describe the historical reasons for the current dominance of p-type Si in photovoltaics. We will then describe the key technological advantages and disadvantages of n- and p-type silicon for solar cell manufacture, from basic material properties, through to ingot growth and cell fabrication issues. Finally, we will provide an overview of the recent advances in simple, low-cost industrial n-type silicon solar cells, and their prospects for overtaking p-type silicon as the dominant material in photovoltaics in the medium term.