Transition from silver-to copper-based screen printed SHJ solar cells

Abstract

In this work, we demonstrate the possibility to reduce silver consumption for highly efficient silicon heterojunction (SHJ) cells by screen printing using low temperature paste based on silver, silver-coated copper or pure copper particles. The achieved grid fingers were characterized towards the line and contact resistance as well as the printed width. The most promising pastes with silver or silver-coated-copper particles allow printing of 35 μm narrow fingers with low line resistance of well below 10 Ω/cm. Simulations show that the achieved grid fingers, lead to very low silver consumption. Comparing cost to efficiency optimization shows that the most cost-effective cell has substantially lower efficiency. This might enable the introduction of alternative low silver or silver-free metallization techniques. To show the currently available options to save silver in screen printed busbarless SHJ cells, samples were produced with specific silver consumption of 7.5 mg/W and even below 5 mg/W if the rear side was realized with a pure copper paste. In another test, silver-based cells with same level of efficiency, improved bifaciality and reduced silver laydown (1/3 compared to reference) around 8 mg/W were successfully introduced into modules.