As direct band gap semiconductor, CIGS thin film solar cells has developed rapidly in recent years. Nano-ripples on transparent layer of CIGS solar cells can improve the light absorption. The photoelectric conversion efficiency improved and the thickness of solar cell decreased with the requirement of optical absorptivity. This study proposed a key technological point concerning the obtainment of perfect LIPSSs using picosecond laser with different beam pattern. Linear sweep in parallel to the laser polarization direction was performed using a Nd:VAN laser system with 10-ps Qswitched pulsed at a central wavelength of 532 nm with a repetition rate of 1 kHz. The nanostructure with different characteristics were obtained at different laser fluence and scanning speed which was focused with circular spot. The linear spot pattern can improve the processing efficiency greatly. In this way, three kind of morphologies were obtained successfully at the same parameter, which was useful for processing different kind of nanostructures. To our knowledge, it is the first time that we report the LIPSSs formed on CIGS absorber layers. Thus, the proposed technique can be considered to be a promising method for the laser machining of special nonmetal films.
This study was performed using picosecond pulses to obtain the three-dimensional micro-nano-hierarchical porous structures on the surface of titanium via the combination of the ablation and the deposition of ablated particles. For the repetition rate of 100 kHz and the scanning speed of 10 mm/s, there were secondary nano-tree-like micro-nano structures via the deposition of the ablated material formed on the primary microstructures. However, when the scan speed decreased, the primary microstructures were invisible owing to too much material deposition. When the repetition rate increased to 500 kHz, the ablated particles were irradiated by the posterior pulse before deposition onto the surface of material, and agglomerated into spidernet-like nanostructures. Then, the upper layer of the secondary micro-nano structure was molten and came into micro-nano porous fractal structures. Both the secondary micro-nano porous structures showed the hierarchy in the vertical and horizontal direction of the surface of titanium. Contact angle measurement after 3 months indicated that the nano-tree-like micro-nano structures showed super-hydrophilcity, and the spidernet-like nano and micro-nano porous fractal structures showed super-hydrophobicity.