Copper as Cost-Effective Alternative to Silver for Si Solar Cell Metallization - Status and Outlook
Creators: name: Clement, Florian
name: Lorenz, Andreas
name: Bartsch, Jonas
name: Brand, Andreas
name: Huyeng, Jonas
name: Keding, Roman
name: Kluska, Sven
name: Maarouf, Fadi Mahmoud
name: Nekarda, Jan
name: Ourinson, Daniel
name: Pingel, Sebastian
name: Schube, Jörg
name: Preu, Ralf
name: :Unav
Publisher: name: Fraunhofer-Gesellschaft
Year: 2024

description: As the photovoltaic (PV) industry continues to advance rapidly towards terawatt-scale annual production and installations, it faces significant challenges, particularly in terms of limited resources. The metallization of silicon solar cells, in particular, raises concerns about the availability of silver in a terawatt-scale PV landscape. This necessitates a shift in established production methods and the development of innovative solutions for sustainable production. This paper focuses on the use of copper as the most promising alternative to silver. It is highly likely that copper-based cell metallization will be integrated into industry production lines within the next 5 to 10 years, especially in certain cell technologies. The authors provide their insights on how this challenge will be addressed. Recent results obtained from TOPCon and silicon heterojunction solar cells highlight the potential of copper in leading in a new era of silver-free solar cell metallization. In this work the main two industry-relevant technologies for the realization of Cu-based electrodes on Si solar cell are addressed: • Electroplating of Cu as a conducting layer for the electrodes on a previously plated diffusion barrier (seed) layer (i.e. Nickel) • Screen printing of AgCu or Cu paste on the rear and/or front side of the solar cell with subsequent annealing, curing or firing. Based on both technologies we discuss several promising approaches aiming at significantly reducing the use of silver in solar cell electrodes by partially or completely replacing them with printed and plated copper. Our findings demonstrate that by employing Ni/Cu/Ag electroplating with a very thin Ag capping layer (less than 5mg Ag/cell), even better I-V results (cell efficiency gain up to 0,5%abs.) can be achieved on TOPCon solar cells compared to the silver-based reference cells. Another approach for TOPCon solar cells addresses dual printing using a screen printed high temperatures silver seed layer paste in combination with a low temperature Cu paste, which yields similar results to the reference cells (no efficiency loss) and allows Ag paste savings up to 75%. Additionally, a directly screen printed grid layout with high temperature Cu paste on TOPCon solar cells shows high potential for further optimization. For the first time functional TOPCon solar cells (cell efficiencies above 20%) with a screen printed pure cupper contact are realized. Further results concentrate on Cu-based, fine line screen printed rear and/or front side metallization for SHJ solar cells will be presented at the conference. All approaches presented in this work enable a significant cost reduction compared to the current state of the art (screen printing with 100% silver pastes) and allow significant savings to be made on silver, a highly expensive resource.