Researchers at Germany's Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE) have enhanced the front-side metallization process of silicon heterojunction (SHJ) solar cells by minimizing the use of silver for multi-wire interconnection.

According to Andreas Lorenz, the corresponding author, this method is straightforward to implement, requiring only the utilization of fine line screens along with an optimized grid layout. The researchers focused on optimizing three production parameters: the printing technique, the finger pitch, and the finger width. They emphasized the growing challenge of dwindling critical resources such as silver, indium, and bismuth, making it imperative to reduce silver laydown, especially for SHJ solar cells where silver paste is typically applied on both front and rear sides.

In their study, the scientists specifically investigated silver application on the front side. They compared knotless and standard printing screens, observing that the knotless method resulted in a slightly narrower mean finger width.

Regarding the pitch of the silver fingers, they tested two options: 1.3 mm and 1 mm. Despite the increased shading with the narrower pitch, it led to an improved fill factor, balancing out the short-circuit current density reduction, resulting in comparable conversion efficiency.

The researchers also experimented with three finger widths: 20 μm, 18 μm, and 15 μm. They found that a width of 15 μm allowed for a more efficient grid layout, reducing silver usage by 5 mg compared to 20 μm, with a 0.14% increase in efficiency.

Utilizing the optimized parameters, they fabricated solar cells with improved efficiency using the knotless fine-mesh screen, 1 mm finger pitch, and 15 μm finger width. These cells demonstrated an average conversion efficiency of 23.2%, a 0.17% gain compared to reference cells, along with a reduction of ~2 mg in silver paste laydown.

Their research, presented in "Towards a cutting-edge metallization process for silicon heterojunction solar cells with very low silver laydown," in Progress in Photovoltaics, involved collaboration with scientists from Yageo Nexensos GmbH, a German electronic components company.