Advanced metallization with low silver consumption for silicon heterojunction solar cells

Abstract

In this work, three industry-related metallization approaches for silicon heterojunction (SHJ) solar cells are presented which are aiming for a reduction of silver consumption compared to conventional screen-printing of low-temperature silver pastes. The presented results are achieved on large-area cells (area of 244.3 cm2). Firstly, the cell results reveal that with silver-coated copper pastes for screen-printing comparable results as with pure silver pastes can be achieved but with a potentially reduced silver consumption of 30%. Median efficiencies of 21.6% are achieved in both cases utilizing a five busbar cell design. A second approach to reduce the silver consumption is the use of inkjet-printing. The influence of the inkjet-printed layer number per contact finger on the cell performance of busbarless cells is investigated. A maximum conversion efficiency of 23.3% of an inkjet-printed solar cell is achieved within this study. Thirdly, a novel printing technology established at Fraunhofer ISE, called FlexTrail-printing, is introduced. By utilizing the same Ag nanoparticle ink like in the case of inkjet-printing, the finger width is reduced from 75 ± 1 µm down to 16 ± 1 µm on alkaline textured SHJ solar cells. To the authors’ knowledge, this is the smallest feature size ever published on ITO-coated, textured silicon surfaces. A maximum conversion efficiency of 23.7% is measured (busbarless cell). Only 0.3 ± 0.1 mg Ag nanoparticle ink is consumed during FlexTrail-printing on a large-area wafer with a front grid of 80 fingers.