+ 09.08.2011 + The Institute for Solar Energy Research Hamelin (ISFH) increases the conversion efficiency of scre­en-prin­ted silicon solar cells from today’s 17.0 to 18.5% to a new record value of 19.4%.

A 200 nm thin SiO2/SiNx double layer at the rear side of the solar cell enables the im­pro­ve­ment. About 80% of today’s industrially manufactured solar cells apply p-type crystalline Czochralski (Cz) silicon wafers in combination with scre­en-prin­ted me­tal contacts. Hence, efficiency improvements for this type of solar cell are highly relevant for the photovoltaic industry and represent an intensive field of research world­wi­de.

Within just one year the ISFH implemented a baseline process with up to 18.5% conversion efficiency for p-type 125x125 mm2 Czochralski silicon solar cells applying scre­en-prin­ted me­tal­liza­ti­on. The solar cells are processed using equipment similar to industry production tools. “The pro­gress was achieved by a close collaboration with industry part­ners and by research projects funded by the German Federal Ministry of En­vi­ron­ment”, explains Dr. Thorsten Dullweber, head of the research group “production pro­ces­ses”.

Se­bas­ti­an Gatz, a PhD student at ISFH, modified the baseline process at the rear side of the solar cell. A SiO2/SiNx double layer is removed on 10% of the cell area by laser ablation within seconds. Hence, the scre­en-prin­ted alu­minum rear metallization only contacts the silicon wafer within these contact openings. The modified cell rear improves the reflection and reduces charge carrier recombination which increases the current and the voltage of the solar cell. The cell front side is metalized by double screen printing which results in reduced contact finger width and hence less shadowing loss. These technical improvements increase the conversion efficiency from 18.5% up to 19.4%.

„This result represents a world record for Cz-si­li­con so­lar cells me­tal­li­zed by screen printing on industry relevant wafer area“, says Prof. Dr. Rolf Brendel, Director of the ISFH, and he adds: “We will further improve and simplify the process within future research projects in order to further reduce the costs of photovoltaic electri­ci­ty”.

More de­tails on the process sequence and the solar cell results are published in S. Gatz et. al, Phys. Status Solidi RRL 5, No. 4, 147–149 (2011)

Institute for Solar Energy Research Hamelin (ISFH) 2011