It is a long-standing dream of the solar industry to replace the expensive silver in the contact fingers of solar cells with copper to the greatest extent possible, or even entirely. Now, Chinese manufacturer Aiko Solar has announced a breakthrough for its ABC (All Back Contact) modules. According to the announcement, the ABC module in the “Stellar” series is the world’s only commercially available double-glass module with copper connections.
The emphasis here should be on “double-glass module,” as modules with copper connectors instead of silver have been around for many decades. A prominent example is the Saturn cell, which was developed at the University of New South Wales in Sydney, Australia, in the late 1980s and commercialized by BP Solar in 1994. The now-bankrupt US manufacturer SunPower Corp. also used copper in the conductor tracks for its back contact cells. Since the busbars are located at the edges of the cell and the contact fingers are therefore very long, they have to be thicker, otherwise there will be significant power losses. In this respect, it makes sense that Aiko Solar also relies on copper, which is particularly good at conducting electricity, for its back-contact cells.
There are good reasons why only a few cell manufacturers have opted for copper so far, even though it is significantly cheaper than silver, which is becoming increasingly scarce. This is because copper is pure poison for silicon. Even at room temperature, copper diffuses into the cell. It causes defects in the crystal lattice where the charge carriers recombine before they reach the contact. In the worst case, this can lead to short circuits in the emitter, known as shunts. Simple substitution is therefore not possible, as copper reacts with silicon even at low temperatures, leading to a decrease in cell efficiency. To prevent this, a barrier must be placed between the silicon of the cell and the copper of the contact. Nickel is often used for this purpose. However, this creates another problem, as such metallic conductor tracks adhere less well to the cell.
The press release does not reveal exactly how Aiko has overcome these difficulties. BP Solar and SunPower have already shown that solutions exist. In April of this year, Berlin-based Solyco Solar AG introduced “TECC-Connect,” a connection technology that does not use any silver, lead, or bismuth. According to the company, it is both cost-effective and future-proof.
© PHOTON
