The next generation of solar cells will make a significant contribution to sustainable power supply on a global scale. For current technologies such as PERC (Passivated Emitter and Rear Cell), which are the focus, a team from the Fraunhofer Center for Silicon Photovoltaics CSP has now researched a mechanism that can be used to optimize high-performance cells.
PERC stands for passivated emitter and rear cell, i.e. for cells with a passivated emitter and rear cell. These enable a greater light yield in the rear area of the cell and thus a higher power yield. PERC technology currently dominates the market, can be implemented in inexpensive mass production and enables even more powerful photovoltaics.
Since the highly efficient solar cells of new generations have not yet been researched as well as standard technologies that have been established for decades, new causes of errors, degradation processes or the risk of failure can also be associated with them. The team around Dr. Stephan Großer, project manager in the “Diagnostics and Metrology” group at Fraunhofer CSP, wants to create solutions for this at an early stage. In the now completed project, CE Cell Engineering GmbH was on board, which specializes in technologies and processes for the optimization of crystalline solar cells.
The project partners have jointly tested a new process for solar cell technologies, with the main aim of lowering the series resistance of crystalline solar cells and thus increasing their efficiency. “The contacting of surface structures (emitters) of solar cells with high sheet resistance is currently technically possible, but complex. The series resistance of the contact structure on the solar cell increases due to high contact resistances, which significantly reduces the efficiency of a solar cell. In the project, on the other hand, we were able to lower the series resistance through the use of laser-assisted current treatment and explain the operating principle, ”says Großer.
The subject of the investigations was faulty semiconductor-metal contacts in the cells, in which there was insufficient electrical contact between metal and semiconductor. The team tested whether and to what extent the use of laser-assisted current treatment at the contact points improves the performance of the solar cell contacts. By investigating the microstructure, it was possible to identify the previously unknown physical mechanism of action of contact formation using the Laser Enhanced Contact Optimization process, also known as the LECO process, at the interface between the metal and the silicon wafer. The LECO process is a downstream process that improves the metal-semiconductor contacts and thus increases the production yield.
The researchers at Fraunhofer CSP have also applied for patenting novel methods for electrical characterization and evaluation of LECO process parameters. The tests carried out on the stability of the solar cells showed that the LECO process used did not damage the solar cells.
R&D activities are an important part of increasing the efficiency of solar cells and thus improving the competitiveness of solar energy and thus saving CO2 . The results of the research project are a helpful building block for us in developing and manufacturing innovative machine technology for the world market, ”says Patrick Müller, Managing Director of CE Cell Engineering GmbH.