New metallisation techniques and schemes will be developed in order to improve solar cell and module efficiency and/or to reduce the cost of the metallisation process. Special attention will be paid to the applicability for large-scale production and the environmental impact. Cost comparison will be used to evaluate the potential of the techniques to be developed and focus the partners on pursuing low-cost options. New printing techniques and the related process scenarios will be developed on a laboratory scale, and tested for their potential at a pilot production level. New plating concepts will be developed and tested in an industrial environment.
Screen printing of metal paste is a low-cost technique, since the front grid pattern is defined in a single process step. However, with present technology the line aspect ratio (width vs. height) is too large, resulting in high reflection losses. This may be solved by various printing technologies: Stencil printing, using a full-metal foil with the front grid pattern; Offset printing overcomes the problems related with paste transport through a screen; Roller printing, in which paste supplied by a roller only adheres to protruding regions; Ink jet printing, where the paste is supplied via tiny needles as in desk top printers.
In addition, the total cell processing will be simplified, using new paste firing schemes, and new paste concepts leading to lower series resistance.
Metal plating is a well proven technology for contact formation, and is readily scaled-up to high-volume production. However, it involves additional process steps to define the front grid. Two approaches are: new high efficiency designs (less reflection loss) which counteract the higher costs and a new method to define the pattern of the metal which initiates the deposition.
The performance, cost, through-put and selectivity of the electro-less plating bath will be improved by optimizing the chemical composition.
Expected Achievements and Exploitation
The output of the DOLMET project is expected to be:
Printing of metal paste: Development of an advanced screen printing process with fine-line, high-aspect ratio, and low-cost advanced passivation techniques using new pastes; printing 60 um wide and 20 um thick lines using a stencil and an optimized paste; roller printed 20 um wide metal fingers; evaluation of new printing techniques, such as off-set printing. Plating: A novel electro-less plating solution, forming metal lines with a triangular cross section; a new low-cost and more environmentally friendly plating solution; evaluation of electro-plating in combination with other metallisation techniques; alternative fine line passivating layer opening techniques. Results will be tested and implemented on a pilot production scale.
Funding SchemeCSC - Cost-sharing contracts