European consortium develops innovative solar module assembly technology

Petten - Within the framework of CrystalClear - a large European project on the development of low-cost, highly efficient silicon solar modules - a manufacturing process has been developed to allow modules to be made using very thin solar cells.

An important goal of the current development of solar modules is to enable solar electricity production at costs that are competitive with retail prices, thus achieving so-called “grid parity”. For this, modules need to be produced at costs around 1 € per watt peak power. Silicon solar modules are composed of wafer-like solar cells, which are series connected and encapsulated to form the module. Since the silicon used to make cells represents a substantial part of the total module manufacturing costs it is important to reduce the amount of silicon needed per unit of cell and module power. This results in the use of very thin cells with a thickness of only 0.1 to 0.2 mm. Thin cells, however, are fragile and easily broken during module manufacture. In particular, the stresses induced by the hot soldering process used to interconnect the cells can be so high that they cause damage. This results in reduced module performance or even complete failure during operation.

To enable the manufacture of modules using very thin cells, the CrystalClear consortium and its partners developed and tested a low-stress method of interconnecting the cells using a conductive adhesive. This research is coordinated by ECN as partner of the consortium. Conductive adhesives need curing in order to become active, but this process can be performed at significantly lower temperatures than conventional soldering, whereas the process time is comparable. Curing has been done using halogen lamp heating prior to encapsulation, but a “single shot” process for combined curing of cell interconnections and encapsulation is under development. Such a process would reduce the number of process steps and the process time, which is important for low-cost, very large-scale manufacturing.

Since the quality of the interconnections and the encapsulation is decisive for the lifetime and reliability of solar modules (which often come with a 25 years performance warranty!), innovations in this area require very thorough testing and are extremely rare. CrystalClear researchers have therefore built dedicated equipment, to enable highly reproducible application and curing of adhesives. With this, they have made strings of cells that have subsequently been encapsulated by the industrial partners. The cells used varied in silicon type, thickness and technology. The strings were encapsulated in modules adjacent to strings made with similar cells interconnected by soldering. This allowed a direct comparison of the conductive adhesive with soldering during climate chamber, outdoor and mechanical tests. The tests showed that the conductive adhesives strings performed as well as the soldered cells.

In summary, the CrystalClear consortium has developed a novel method for durable interconnection of very thin solar cells. This further paves the way to low-cost, high performance silicon solar modules and hence, to price-competitive solar electricity.

Editorial note
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For more information: Wim Sinke, coordinator CrystalClear, email pmo@remove-this-part-ipcrystalclear.info, tel. +31 224 564539, www.ipcrystalclear.info.

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