Fundamental studies on the front contact formation resulting in a 21% efficiency silicon solar cell with printed rear and front contacts
The contact formation on high efficiency solar cells using a high temperature process is the subject of this research. The chemical reactions between ink components and solar cell during the contact firing process are studied in detail by thermal gravimetric - differential thermo analysis. The mechanism behind the etching process and the opening of the dielectric layer are explained and the impact of the glass frit is investigated. Based on these studies, a seed layer ink was developed, optimized and tested on silicon solar cells. The developed ink was applied on high efficiency solar cells with printed front and rear contacts. At the rear side, we used a firing stable passivation layer consisting of Al2O3 and SiNx, which additionally resists the reactive compounds of the screen printed Al-paste. After applying laser fired contacts at the rear and light induced silver plating at the front, cell efficiencies of eta = 21% and fill factors of 81% could be measured.