Highly Innovative, Resource-Efficient, Environmentally Friendly, and Cost-Effective Solar cell Interconnection Technology Paving the Way for a lead-free Photovoltaic Industry

The “HochzeiT” project aimed to evaluate Foilmet®, the laser bonding technology invented and patented at Fraunhofer ISE and developed to Technology Readiness Level (TRL) 4, for the mass market in photovoltaics and advance it to TRL 7. Foilmet enables the production of sustainable PV modules that do not require solder, lead, flux, or adhesives.

Given the urgent need for renewable energy to achieve climate goals, the technology is intended to enable environmentally friendly and visually appealing photovoltaic systems that can be produced in a resource-efficient manner using a cost-effective mass production process. This makes an important contribution to the energy transition and to the societal acceptance of solar energy.

Initial Situation

Even today, state-of-the-art technology still involves the use of heavy metals such as lead and cadmium in the manufacture of photovoltaic modules. According to the RoHs Directive (“Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment”), the use of environmentally harmful substances in the production of electronic components is prohibited. However, the directive allows for exceptions, including for the production of solar modules, as there is currently a lack of adequate alternatives. Consequently, the use of lead and cadmium is not subject to the RoHs Directive and remains unrestricted. In view of the massive expansion of photovoltaic systems that is projected and required as part of the energy transition, RoHS-compliant PV technology is highly desirable.

Objective

The “HochzeiT” project aimed to bring the patented Foilmet® technology – which is being developed as part of the (publicly funded) “Liebesbrief” project – to Technology Readiness Level 7 by the end of the funding phase, and to manufacture and qualify modules in standard industrial formats for the first time. The project was accompanied by a comparison with the current state of the art and a cost-benefit analysis.

Approach

The innovative Foilmet® technology enables the production of photovoltaic modules without harmful materials such as lead and flux, thereby significantly reducing the environmental impact. At the same time, the laser-welded aluminum connectors ensure minimal series resistance while maximizing the flexibility of the solar cell string. This solution is not only environmentally sound and cost-effective, but also visually appealing. In this way, it further contributes to the societal acceptance of photovoltaics and additionally offers a wide range of innovative applications in the field of integrated photovoltaics. The project aimed to optimize the technology for the mass market in order to address the challenges of the energy transition in a sustainable manner.

Results

Initially, the project utilized industrial PERC solar cells in the M6 format and equipped them with a contact design adapted to our interconnection technology. This saves approximately 20% in silver compared to the state of the art. The cells were separated and then connected in series using the FoilMet process. To date, three industrial-format modules have been successfully manufactured and measured as part of the project. Both the cross-connection of the individual strings and the module layout were continuously optimized. Most recently, 20 strings, each comprising 18 shingled cells per module, were installed, resulting in an active area of 95 cm x 165 cm.