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All-screen-printed back-contact back-junction silicon solar cells with aluminum-alloyed emitter and demonstration of interconnection of point-shaped metalized contacts

: Woehl, R.; Rüdiger, M.; Biro, D.; Wilde, J.


Progress in Photovoltaics 23 (2015), Nr.2, S.226-237
ISSN: 1062-7995
Fraunhofer ISE ()

In the following, high-efficiency back-contact back-junction silicon solar cells with aluminum-alloyed emitter are described. First, the theoretical background for the cell concept is explained. To that purpose, the bulk lifetime and the front surface field characteristics are considered. Three different process sequences for the phosphorus-diffused profiles on the front and back surfaces are depicted: One exhibits a shallow field, and two sequences have deeper, driven-in profiles. For realizing high efficiencies, such cell structures must meet several prerequisites, such as firing-stable front and rear passivations, and functional small screen-printed Al structures. Furthermore, it must be possible to create contacts on the Si surfaces using the driven-in P-profiles. With such a structure, cell efficiencies of 20.0% are reached. An analysis of the series resistance and area-weighted recombination is performed. The results are compared with the measured cell parameters. Two-dimensional simulations show the efficiency potential when decreasing the width of the backside field and when a cell structure, which would inhibit a passivated aluminum-alloyed p+-emitter, is created. Also, an advanced concept is demonstrated where a point array of both polarities on the cell backside is interconnected externally on module level. To that purpose, the cell is soldered to a printed wiring circuit board by using a reflow soldering process.