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Screen printed cells achieve lab breakthrough

The Institute for Solar Energy Research Hamelin (ISFH) says it has increased the conversion efficiency of screen-printed silicon solar cells from today’s 17%-18.5%, to a new record value of 19.4%.

By Renewable Energy Focus staff.

A 200 nm thin SiO2/SiNx double layer at the rear side of the solar cell enables the improvement, according to sources at ISFH.

How does the process work?

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 PV industry and represent an intensive field of research worldwide.

Within a year the ISFH reports that it implemented a baseline process with up to 18.5% conversion efficiency for p-type 125x125 mm2 Czochralski silicon solar cells - applying screen-printed metallisation. The solar cells are processed using equipment similar to industry production tools.

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. Therefore the screen-printed aluminum rear metallisation only contacts the silicon wafer within these contact openings. The modified cell rear reportedly improves the reflection, and reduces charge carrier recombination which increases the current and the voltage of the solar cell.

The cell front side is metalised 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%.


 

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