In the past, photovoltaics – and indeed many of the other green technologies – have suffered from the perception of being too expensive to implement, and therefore with far too long a return on investment. But now, as we become more experienced at building solar panels and the technologies surrounding this, the costs are coming down – to a point where they now overlap with the costs of the more traditional methods of generating electricity. Couple this with the drive towards more use of green and renewable technologies, and you have an industry that has seen incredible growth.
There is no doubt that the current economic crisis has had an impact on the industry, but that means that solar panel manufacturers are looking to cut manufacturing costs and at the same time make their products more efficient at converting sunlight into electricity – and laser processes are one of the leading methods for achieving those efficiency improvements. As demand has fallen, solar panel manufacturers are now in a position to consider improving their production methods – where previously they were already full to the brim with orders and had no incentive to review these methods.
Laser-based tools are at the heart of these efficiency drives. In the thin film area, lasers are replacing mechanical scribe heads. Previously, diamond or carbine tipped heads would be used to scratch lines on the film. Lasers allow this process to be done faster using a non-contact technique (so the tips don’t wear), and the lines can be scribed finer, therefore increasing the efficiency of the panel.
Another technology where lasers make a difference is in edge deletion, where the laser goes around the outside of the panel, removing a strip of 10-12mm of all coating materials down to bare glass, so that the panel can be bonded to the substrate or superstrate. Previously, this was done with sandblasting or abrasive diamond wheel techniques, both of which have problems with consumables, high cost and glass damage. They are beasts to maintain and very expensive to run. Again, lasers provide a very clean, non-contact alternative.
In the crystalline silicon market, there are a number of laser-based techniques for fabricating front and rear-side contacts that increase efficiency. Consequently, laser tools are replacing screen printing and other basic methods of electro-plating those contacts, providing reduced shadowing loss and better contact with the silicon.
There is also a technique called laser doping, a clever and elegant solution whereby a phosphorous dopant is put on the silicon nitride surface layer of a cell, and the laser does two things at once: it melts and ablates the silicon nitride, slightly melts the silicon underneath, and migrates the phosphor doping into the silicon – all at the same time. This creates a self-aligned trench for metallisation. The cell is then placed in a bath for plating, and the contacts magically form exactly where the laser processing occurred.
There are many types of laser that are suited to photovoltaics, with factors such as the material being used or the particular geometry of the cell dictating exactly which laser is best. For thin films, for example, the majority of people are using nanosecond lasers. For Pattern 1 (P1), the choice is usually infrared, and for P2 and P3, it’s a green laser. There are people using UV for P1, and some talking about using picosecond options.
Right now, the traditional markets for lasers are at a low point. There are hardly any areas of the economy that aren’t being affected at the moment. However, the good news is that there is plenty of government money flowing into renewable energy sources and investment in converting legacy electricity generating methods over to renewable energies. As lasers offer a way of improving those technologies and lowering the cost, photonics is therefore a key enabler. This makes it a great market to be in. It might take a while, given the current economic climate, but the growth is going to come back.
In the long run, the solar panel market is likely to be less cyclical, and the market is huge. Even just a small percentage of the world electricity market translates into thousands of lasers. So sheer size and underlying drivers are two elements that make me very bullish about the photovoltaics market; lasers will have a huge part to play in this.
