Resource efficiency, reuse and repair in solar cell processing

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Resource efficiency
In crystalline solar cell manufacturing, when wafers are being processed into solar cells, several wet chemical etching and cleaning steps are implemented, which have negative impact on the environmental footprint. By reducing and avoiding certain chemicals or metals (e.g. HF, Pb, Ag, Al) and using less pure or recycled chemicals, waste can be reduced and the ecologic footprint of solar cells and panels can be improved.
Especially silver is an important element, as it is used in most solar cells (>98%) currently produced, providing the metal contact that “collects” and “drains” the current from the solar cell, resulting in todays silver consumption for PV of about 15% of the total silver market with the expectation to rapidly grow further.
In the Eco-Solar project, ISC-Konstanz will experiment with different solar cell architectures, to minimise the use of Ag. In addition, an innovative interconnection scheme enabled by Apollon’s module design, will avoid soldering of a contact tape onto the rear side Ag pads and the front side busbars. Only the small contact fingers on the front side are needed.
In addition, ISC-Konstanz and SoliTek are testing an alkaline saw damage removal and texturisation to replace the current state of the art concentrated HF:HNO3 mixture, HF reduction in cleaning process is also investigated. Advanced processes for emitter formation are developed that will enable higher throughput, resource efficiency and avoid the needs for chemical phosphorous glass layer removal (PSG-removal).
AIMEN will further develop advanced laser treatment, in order to minimize the cut-off area at the wafer edges to a negligible fraction of the whole wafer area, to avoid the wet chemistry normally used to separate the front and rear of the solar cells.
In total, the innovations aim to save at least 60% of silver and almost 90% of chemicals, which will be assessed by bifa in the LCA.

Reuse of water during cell processing
During the processing of wafers in to solar cells, water is mainly used for cleaning: after each chemical processing step, the wafers are rinsed with de-ionised, ultra-clean, water. Afterwards, the water that goes down the drain, is often of higher quality than the water contracted from the tap.
One of the cornerstones of environmental protection in Europe, is the protection of water resources, of fresh and salt-water ecosystems and of the water we drink and bathe in.
With the example of Solitek where solar cell processing with a production capacity of 80MW, consumes about 54.000m3 of de-ionised water per year, it becomes clear that recycling systems for waste water can have a large impact.
Therefore, ISC-Konstanz will look into industrial viability of recycling systems for waste water, and investigate its potential for saving more than 90% in solar cell processing, while bifa will assess the environmental benefits via an LCA.

Solar cell repair during manufacturing
In order to capitalise on the value a solar cell represents, repair of defect solar cells within the solar cell process can represent a significant financial and ecological impact. AIMEN coordinated the EU-funded project REPTILE, in which ISC and INGESEA participated as beneficiaries. The project provided preliminary work on a system that is able to automatically select and cut out or isolate non-defective areas in defective cells and wafers, called the Cell-Doctor.
Within the Eco-Solar project a fully operational protoptype is to be built. ISC will evaluate the rejected solar cells with an automated system for defects recognition. AIMEN and INGESEA will further develop the accuracy of the Cell-Doctor prototype, aiming to avoid 50% scrapped cells. Moreover, this technology can be used to evaluate solar cells after end-of-life modules return to the factory for recycling and reuse.

In an LCA bifa will assess the environmental benefits of the repair process for solar cells.

to the second process step
cutting and wafering of Si ingots

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to the fourth process step
module design