Fine-line Silver Pastes for Seed Layer Screen Printing with Varied Glass Content

Abstract

This paper presents the development of a fine line seed layer screen printing paste with low silver lay down ∼ 30mg per cell for front side metallization. The contacts of these seed layers are subsequently thickened with light induced plating. Standard screen printing pastes contain between 2%-5% glass frit while aerosol seed inks contain > 15% glass frit. The amount of glass needed for best contact formation in fine-line seed layer screen printing paste is unknown. In this study, an empirical approach varying the glass content in the seed layer pastes has been chosen. To adjust the glass amount to the low metal content, the glass content was varied at 4%, 8% and 12% for the printed seed layer. 156 x 156 mm2 p-type silicon solar cells with 90Ω/sq. emitter were used. Contact fingers < 60μm wide and 2μm high were achieved. It was found that an increase in glass content improves the ability to achieve low contact resistance of about 5mΩcm2 even under moderate firing conditions. Open circuit voltages of Voc = 632mV, fill factors of = 77% and efficiencies up to η =18% have been achieved. Additionally, an increase in glass content from 4% to 8% improved the maximum contact adhesion after nickel and copper plating from 0.5N/mm to 1.1N/mm.