Single Print Metal Stencils for High-efficiency PERC Solar Cells

Abstract

Industrial silicon solar cells like Passivated Emitter and Rear Cells (PERC) typically apply a screen-printed (Ag) front contact with a single print process using a mesh screen. It has been shown that using stencils instead of screens improves the finger profile leading to slightly higher cell conversion efficiencies. However, so far stencil printing required an extra printing step for the busbars since conventional stencils do not support H-pattern designs. In this paper, we evaluate a novel "single print" stencil from ASM AE that allows to print busbars and fingers in a single print step. We apply the novel single print stencil to high-efficiency PERC solar cells and compare it to today's industrial screen printing processes (single print and dual print) as well as to a high performance dual-printed front side grid applying a stencil for the fingers and a screen for the busbars. The printed finger width ranges from 35.8 ± 2.3μm for 30μm stencil opening to 46.7 ± 3.4μm for 40μm screen opening which leads to an 0.5%abs increased metallized area on the front side of the screen printed fingers compared to the stencil printed fingers. The resulting average finger height is 22.3μm for the stencil groups and 11.9μm for the screen printed Ag finger which leads to a difference in the finger line resistance and an additional series resistance contribution for the screen-printed cells of 0.05Ωcm2. We achieve almost identical PERC cell efficiencies with the single print stencil and the dual print stencil process obtaining best values up to 21.1% and average values of 21.0%. In contrast, both screen printed groups achieve 0.2%abs lower average conversion efficiencies mostly due to the lower Jsc and FF. The advantage of the dual print process compared to single print is shown in the increased Voc by 1 to 2mV due to the used non-firing through Ag busbar paste. With these results we demonstrate that the single print stencil process saves two process steps compared to dual print using a stencil while obtaining the same PERC cell performance with an efficiency gain of 0.2%abs compared to today's industrial screen print processes.