Optimisation of Screen-Printed Metallisation for Industrial High-Efficiency Silicon Wafer Solar Cells

In the photovoltaic industry, screen printing accounts for majority of the metallisation processes for silicon wafer solar cells. Contact formation by co-firing of front and rear screen printed metal pastes for mainstream p-type standard solar cells is a well-established process. It is of utmost importance to use front and rear metallisation pastes that are co-tiring compatible. hi this paper, we describe a methodology for front and rear paste selection and process optimisation. We explore the usage of HF dip (20 seconds) on -finished cells to differentiate between over-fired and under-tired contacts. Two commercially available front Ag pastes (paste 'A' & paste 'B') with fine line printing capability were tested along with two commercially available rear Al pastes (paste 'C' & paste 'D'). Firing optimisation was conducted to achieve a one-Sun till factor of 80.7 % and a series resistance at maximum power point (MPP) of 0.4 Omega cm(2) at the optimised firing profile. The Al paste 'C', which resulted in a better and more uniform back surface field at the optimised profile, was selected to study the effect of post-metallisation.HF etching. By choosing the correct combination of metal pastes, at the optimised tiring profile, efficiencies of 18.5% were realised for standard screen-printed 156 nun x 156 nun p-type pseudo-square monocrystalline solar cells. (c) 2013 The Authors. Published by Elsevier Ltd.