Blistering in ALD Al2O3 passivation layers as rear contacting for local Al BSF Si solar cells

Abstract

Random Al back surface field (BSF) p-type Si solar cells are presented, where a stack of Al2O3 and SiNx is used as rear surface passivation layer containing blisters. It is shown that no additional contact opening step is needed, since during co-firing local Al BSFs are induced at the location of these blisters. The best fill factors and short circuit currents are obtained in the case of (i) a hydrophobic pre-passivation cleaning, since it leads to a small density of larger blisters, and (ii) 10 nm of Al2O3, where the blistering size still increases during firing thanks to additional out-gassing. There is an apparent gain in J(SC) and V-OC of, respectively, 1.3 mA/cm(2) and 5 mV for the best random Al BSF cells compared to full Al BSF reference cells, because of better rear internal reflection and rear surface passivation. (C) 2012 Elsevier B.V. All rights reserved.