Lasers Lower Cost of Making Photovoltaic Cells

Trumpf's new Trumicro Series of ultra-short-pulse lasers are said to lower the manufacturing cost of photovoltaic cells, as well as enhancing their performance. 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 100kHz result. An optimised pulse-to-pulse overlap makes for a clean kerf and minimises negative heat effects. The compact Trumpf Trumicro Series 3000 with wavelengths of 1,064 and 532nm are suitable for P1, P2 and P3 patterning. Due 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, according to the company. 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 suitable 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 Trumicro 7050 is recommended for this application, as it can process large areas at production speed, reliably and securely. It generates pulses with 30 nanoseconds duration at an average power of 750W. 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 due to their high 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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