Photovoltaics: Precision and throughput in production
Hair-thin conductors, thin film layers and drill holes accurate to the micrometer: The success of solar power rests on tiny features. Lasers are the technological key to higher precision, high throughput and new designs.
In the production of thin-film solar modules, conductive and photoactive layers are deposited.
After every coat, the surface is structured. This forms the individual cells and connects them together into a module. Structuring with a laser subdivides thin-film solar modules precisely, selectively and without contact. And, it is reliable with short processing times. In the production of modules with amorphous silicon and cadmium telluride, nanosecond lasers in the TruMark series with wavelengths of 532 and 1064 nanometers are used.
For edge deletion, the edges of the layered system are ablated in order to prepare for lamination with a second glass substrate. Fiber-guided lasers with average power over 500 watts can achieve the highest ablation rates, up to 50 square centimeters per second. These ablation rates allow the cost-effective use of lasers even over large areas and with short cycle times.
Lasers are increasingly used for crystalline solar cells because they enable fast processing and are easy to integrate into production lines. Thus laser edge insulation is often used in the production of the cells.
Dosing of the circumference in production automatically yields short circuits on the front and back sides. In laser edge insulation, the laser makes a separation line at speeds of over 700 millimeters per second, which eliminates the short circuit.
Laser processing enables solar cells with higher efficiency; for instance, designs with contacts on the back side. Lasers work contact-free, so they can be positioned quickly without mechanical load. These properties allow thousands of drilling operations per second, to create guide holes for contacts on the back side.The drill holes cover only a few percent of the surface and increase efficiency.
The laser allows specific contacts on the back side of the solar cells. This can be achieved in two ways. Either the contacts are "shot" through a laser system on the wafer, referred to as "laser-fired contacts", or passivization layers of SIO or SIN are selectively ablated without damaging the silicon. Then the rear side is entirely coated with a metallic coating. The reflectivity of the rear side is increased, and power loss at the contact points is very low.