12 April 2011

Something new under the sun

Trumpf’s new TruMicro Series of ultra-short pulse lasers are lowering the manufacturing cost of photovoltaic cells as well as enhancing their performance. Maximising cell efficiency is the result of extremely precise and fine surface structuring and these lasers do this far better and more cost effectively than 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 tensions, depending on the cell width, can be set.

The transparent conductive oxides are usually processed with lasers in the infrared wavelength. At typical feed rates, repetition rates of over 100 kHz result. An optimised pulse-to-pulse overlap makes for a clean kerf and minimises negative heat effects.

The small and compact Trumpf TruMicro Series 3000 with wavelengths of 1064 and 532 nanometres 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, presents a particularly high challenge for the laser process. The same applies to the structuring of molybdenum. For this application, nanosecond lasers are still used but picosecond lasers offer a far better solution.
With these lasers, the material is ablated with ultra-short pulses without significant heating of the process edge zone. This prevents cracking, melting and exfoliation of the layers. Trumpf Series 5000 picosecond lasers are ideal for this task. They have a wavelength of 1030nm 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.

Edge deletion: lasers replace sandblasting
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 30 nanoseconds duration at an average power of 750W.

Crystalline solar cells; lasers reduce the ‘per Watt’ costs
Up and coming laser applications include the selective ablation of passivated layers on crystalline solar cells. Trumpf TruDisk lasers with ultra-short pulses and high pulse energies are particularly well suited to this work thanks to their excellent beam quality.
The simple scalability of the laser output enables a higher production capacity to be achieved. And the high beam quality in the ultra-short pulses significantly improves solar cells efficiency. This will result in a significant reduction of the ‘per Watt’ cost of solar cell performance in the future.

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