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N-type multicrystalline silicon wafers and rear junction solar cells
Published online by Cambridge University Press: 30 November 2005
Abstract
N-type silicon presents several advantages compared to
p-type material, among them, the most important is the small capture cross
sections of metallic impurities, which are neatly smaller. As a consequence
lifetime and also diffusion length of minority carriers should be neatly
higher in n-type than in p-type, for a given impurity concentration. This is
of a paramount interest for multicrystalline silicon wafers, in which the
impurity-extended crystallographic defects interaction governs the
recombination strength of minority carriers. It is experimentally verified
that in 1.2 $\rm \Omega $ cm raw wafers lifetimes about 200 $\mu $
s and diffusion
lengths around 220 $\mu $
m are measured. These values increase strongly
after gettering treatments like phosphorus diffusion or Al-Si alloying. Scan
maps reveal that extended defects are poorly active, although in regions
where the density of dislocations is higher than 106 cm-2. Abrupt
$p^{+}n$
junctions are obtained by Al-Si alloying after annealing between
850 and 900 °C, which could be used for rear junction cells. Such cells
can be processed by means of similar processing steps used to make
conventional p-type base cells.
- Type
- Research Article
- Information
- The European Physical Journal - Applied Physics , Volume 32 , Issue 3 , December 2005 , pp. 187 - 192
- Copyright
- © EDP Sciences, 2005
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