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Environmentally clean efficient, and easy to contact crystalline silicon solar cells (EC2 CONTACT)


EC2CONTACT achieved a significant step in terms of health and environment by successfully developing lead free silver and aluminium pastes for solar cell metallisation. Lead free materials developed by the Consortium perform comparably to traditional leaded pastes: Newly developed lead free Ag paste achieved a Fill Factor of 77.1% and an efficiency of 16.9% on 40W/sq emitter SiNx cells. The Al paste yields electrical results comparable with reference pastes - Fill Factor of 76.5% and efficiency of 17.1% on 60W/sq emitter SiNx cells but also shows large improvement of the mechanical properties of the deposit: bowing of the 310µm cells decreased by 15%. Avoiding lead in metallisation pastes is still a challenge. Leaded glasses are known to be most effective in providing excellent contact and adhesion to the silicon wafer in solar cells. However lead is environmentally hazardous and has multiple toxic effects. Metalor believes in an increasing demand for “green” products also in the field of photovoltaics. As part of its long term strategy focussed on environmentally friendly products and processes Metalor is committed to develop and manufacture lead free silver and aluminium pastes. This approach fits Consortium Partner RSS whose aim is to manufacture lead free products.
To make progress in contact formation, a new approach is necessary. Almost no improvement has been made in this topic for the last 10 years, the same pastes are being used as 10 years ago. To be able to use environmentally benign components, to accomplish higher efficiencies, and a robust process, a scientific approach was followed. Hypotheses were made to predict the functions of components in paste and to predict behaviour during processing. These hypotheses were tested by simple experiments and detailed characterisation. Using the results from these measurements and experiments, models were made to describe the behaviour of components and the complete system during deposition, drying and sintering. These models were tested and used to guide the development to improve contact formation. One of the outcomes of our scientific approach is the way we experiment and test new metallisation components and processes. A simple test methods on components is used to see whether they perform as predicted and to avoid expensive, large-scale experiments involving cell processing with many process settings.