Latest back contact technology for heterojunction solar cells in mass production

Solar cells made in Europe can set themselves apart from the competition through highly efficient technologies and compliance with environmentally friendly produc-tion processes and standards. This is where the EU-funded joint project PILATUS comes in, which aims to create three digitalised pilot lines for the production of silicon wafers, solar cells and PV modules in Europe by 2025. The aim is to transfer the latest back-contact technology for heterojunction solar cells to mass production. The Fraunhofer Centre for Silicon Photovoltaics CSP is applying its expertise in the field of inline and offline diagnostics and metrology of solar cells using its digitally controlled measurement and classification platform.

© Fraunhofer CSP
The "MK4" measurement and classification platform available at the Fraunhofer CSP offers process and data analytics for high-performance photovoltaic production.

The quality and performance of the European-based production of materials and components for photovoltaics, such as silicon wafers, solar cells and modules, is essential for the further development of the industry. The aim is to reduce dependency on imports at all stages of production and to create competitive framework conditions. The focus is on the production of high-quality and efficient solar cells using the latest technologies. Another aspect of manufacturing in Europe is compliance with environmentally friendly production standards. This includes the use of recycled materials, the use of renewable energies in production and the minimisation of waste and emissions.

The EU-funded PILATUS project addresses this issue and aims to strengthen the competitive advantage of the "Made in Europe" factor with digitalised pilot lines, in which the entire value chain remains in Europe and complies with the latest environmental standards. The project uses the patented tunnel IBC technology to demonstrate the goal of mass production of solar cells in M10 format (monocrystalline silicon as material, 10 inch diameter). Tunnel IBC technology reduces losses in the solar cell and increases efficiency. A specific type of back-surface contact makes it possible to utilise the entire front surface of a solar cell to capture light and thus generate electricity. The project also aims to minimise the environmental footprint by using recycled materials and eco-design practices to facilitate the dismantling of photovoltaic modules and production facilities that comply with environmental standards.

The pilot line for photovoltaic modules is expected to reach an annual production capacity of at least 170 megawatts, accompanied by a cell capacity of 190 megawatts. By combining inline measurement technology and Industry 4.0 concepts along the entire production chain, the cells and modules are analysed throughout the entire manufacturing process in order to draw conclusions about possible defects and weak points directly during production. This ensures that a yield of over 90 per cent is possible at the end of the project and that photovoltaic modules achieve a service life of over 40 years.

The work at Fraunhofer CSP is aimed at developing an automated inline metrology system in which artificial intelligence (AI) is used during the metrological data chain. Initially, AI will be used to extract features from sample image data and to correctly recognise and classify features and defects. Further down the chain, AI-based algorithms will be applied to the extracted classification and feature data from the measuring device to find patterns that indicate process errors and can be used as direct feedback for process control. "For this purpose, we will use the high-throughput metrology and classification platform MK4.0 located at the Fraunhofer CSP, which will be equipped with IBC inline metrology solutions and sensor technology for statistical cell data analysis and AI image algorithms in the project," says Dr Marko Turek, acting group leader "Diagnostics and Metrology Solar Cells" at the Fraunhofer CSP.

For offline solar cell characterisation, Fraunhofer CSP will detect defect areas on the IBC solar cells in the nanometre range and analyse them using microstructural methods in order to identify the production steps causing the defects. In addition, the degradation stability of the IBC solar cells is ensured with offline test procedures using established tests for light-induced degradation and UV degradation. The IBC solar cells are tested in an LED-based lighting unit with a customisable light spectrum and a subsequent electrical performance analysis. "With this combination of production-related inline metrology solutions and highly complex laboratory methods, we not only support efficient production, but also overall product quality," adds Turek.