Trumpf has revealed that its new TruMicro series of ultra-short pulse lasers has been used successfully in photovoltaic cell manufacturing, lowering the manufacturing costs of components and enhancing their performance. The precise and fine surface structures that the laser can produce results in a highly efficient photovoltaic cell, which can be produced more cost effectively than possible by alternative processes.
In the production of solar modules from amorphous silicon (aSi) or cadmium telluride (CdTe), conductive and photoactive films are deposited on large substrate areas, such as glass. After every deposition, the laser subdivides the surface so that the cells created are automatically switched in series by the process sequence. In this way cell and module voltages, depending on the cell width, can be set.
The transparent conductive oxides are usually processed with lasers in the infrared wavelength. At typical production line feed rates, repetition rates of over 100kHz are required. An optimised pulse-to-pulse overlap makes for a clean kerf and minimises negative heat effects.
The small and compact Trumpf TruMicro 3000 with wavelengths of 1064 and 532nn are ideal for P1, P2 and P3 patterning. Thanks to their high pulse-to-pulse stability, these diode-pumped solid-state lasers achieve very good processing results. They can also be easily integrated into existing systems because of their advanced cooling design. The patterning of thin-film cells made from Cu (In, Ga) (S,Se)2, also known as CI(G)S (pronounced 'cigs'), particularly difficult to process using a laser, as does the processing of molybdenum - and application in which nanosecond lasers are still used, but picosecond lasers will, Trumpf says, offer a better solution. Picosecond sources are able to ablate material without significant heating of the process edge zone, which prevents cracking, melting and exfoliation of the layers. Trumpf Series 5000 picosecond lasers are ideal for this task. They have a wavelength of 1,030nm for structuring molybdenum and 515nm for processing photoactive material and patterning the front of the contact. Additionally these Trumpf TruMicro picosecond lasers have output power up to 50W which significantly reduces process costs.
To protect thin-film solar modules against unfavourable environmental influences – especially against moisture – a width of approximately 10mm of the layer system is ablated along the edge and covered with laminated film. The traditional method employed is sandblasting but Trumpf TruMicro lasers provide a far more suitable process. The TruMicro 7050 is recommended for this application which can process large areas at production speed, reliably and securely. It generates pulses with 30ns duration at an average power of 750W.