Rau AG [Frankfurt stock exchange: R8R] has developed a process which uses inexpensive nickel in busbar metallisation for the electrical contacting of solar cells. The coating process includes both the front and rear sides of the cell within a production tool. This process, which is immediately available, significantly differentiates Roth & Rau from its competitors.
Depending on the contact technology, a saving of between 50 and 70% in expensive silver and therefore a significant reduction in the production cost of solar cells can be achieved. A further benefit from the process is the fact that nickel is a readily available material. This means that solar cell manufacturers are not tied to specific suppliers as is the case with other materials.
The HELiA system, which was developed primarily for the production of high efficiency heterojunction cells, coats the solar cells with nickel in a shortened system configuration to form the front and rear busbars. This is achieved by means of a sputtering process. In contrast to other systems, the HELiA system permits simultaneous processing not only of the rear surface but also of the front surface on which there is a significantly greater potential for savings.
A further decisive benefit of this new process is the outstanding adhesion of the cell connectors to the front and rear surfaces of the solar cell as a result of the nickel metallisation in standard soldering processes. The metallisation of the fingers can thus take place regardless of the electrical characteristics of the busbar and be optimised to match them. In this way, the metallisation of the fingers is de-coupled from the solderability of the busbar, thereby enabling the use of new pastes and metallisation processes that do not currently achieve reliable solderability. The performance of solar cells coated with this process is comparable with that of solar cells metallised in the conventional way by screen printing.
The concept and associated system will be presented at the Meyer Burger stand (Hall 3, E2) at the upcoming EUPVSEC trade fair in Frankfurt from 25-28 September.