Laser Materials Processing

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Our lab has also been interested in the laser-matter interactions and their applications. Two current research topics are surface texturing of Si and laser sintering of Cu ink.

Si has a high surface reflectance due to the large refractive index. For the solar cell applications, the surface of Si should be textured to reduce reflection loss and thus increase light absorption. The maximum efficiencies (~25%) of single-crystalline Si solar cells have always been achieved with inverted-pyramid (IP) textures. However, this texture structure has yet to be commercialized because it requires lithographic processes that significantly increase the fabrication cost. We have recently demonstrated that IP structures can be fabricated simply by irradiating the Si surface with a nanosecond pulsed laser, followed by alkali etching. We also showed that this mask-free process is very effective for generating regular surface structures on multi-crystalline Si.

Si solar cell structure using inverted-pyramid texture

The application of metal ink to printed electronics has drawn considerable attention as a route to low-cost fabrication of integrated circuits. The printed metal ink can be utilized in a wide range of areas such as printed circuit boards, antenna tags for radio frequency identification, electromagnetic interference shielding circuits, and transistors. Two steps are required to obtain conductive patterns from metal inks; printing followed by sintering which transforms the ink to a conductive metal track. Compared to typical thermal sintering, laser sintering offers unique benefits of high-speed, localized heating minimizing the substrate damage, synchronization of the sintering and patterning, and compatibility in-situ with the roll-to-roll printing. We have been working on the synthesis of Cu complex inks and their selective sintering by a laser to form highly conductive and adhesive metallization patterns on glass and plastic substrates.

Fig. 1 (Laser sintering of Cu).jpg

                                                                                   (Optics and Laser Technology 2017, 88, 128)


<Demo video of laser selective sintering of Cu ink>