In processes using the ultrashort pulsed laser, the phenomenon that the ablation efficiency is reduced due to the increase of the shielding effect of the generated plume is increasingly caused by the use of the high power and high repetition rate. A new method is needed to prevent a decrease in ablation efficiency in processing using an ultrashort pulsed laser. In this study, the proposed a processing method that can improve the ablation efficiency by providing an efficient escape path of plume, and examine the feasibility of a new processing method. The new method we proposed is a method of laser processing after generating a fine curvature in the polymer as a preliminary preparation. The fine curvature of the polymer produced by the preliminary preparation induces an artificial chimney-like opening along the path of the incident beam during laser processing, thereby enabling the plume to be effectively removed. The experiment for examine the feasibility through a new method was conducted using a 10-picosecond laser of UV wavelength with two optical systems. As a new processing method, when processing with ultrashort pulse laser, it was observed that the ablation efficiency improved.
Cu(In,Ga)Se 2 (CIGS) is a promising candidate for flexible photovoltaics because of its outstanding efficiency and flexibility. Despite its advantages, achieving high-efficiency CIGS solar cells on a flexible polyimide (PI) substrate is challenging as it requires a low-temperature process and relaxation of the thermal expansion. This limitation is critical in CIGS modules, particularly for monolithic interconnection processes by laser scribing. Furthermore, Mo back-contact (BC)-based PI cells are sensitive to each laser processing step. Laser scribing is one of the important processes in thin-film module manufacturing. In this study, for the first time, we applied indium tin oxide (ITO) instead of Mo as a BC layer on the spin-coated PI on soda-lime glass to obtain mechanically durable CIGS modules. The ITO BC-based module not only provides a crack-free CIGS layer but also offers superior device performance owing to the excellent laser scribing quality. Additionally, electrical properties related to respective scribing steps are analyzed in correlation with observed morphologies to evaluate parasitic resistance and optimize the laser scribing conditions. Consequently, a CIGS monolithic-integrated module with 15.03% efficiency at 40.14 cm 2 (16.3% at 0.480 cm 2 ) is fabricated on a novel "soda-lime glass/coated-PI/ITO structure". We propose ITO BC-based cells as promising candidates for achieving highefficiency and flexible CIGS solar modules.
We experimented with two polymer materials with different ultraviolet (UV) wavelength absorption characteristics, which are commonly used in flexible devices, by applying an ultrashort-pulsed laser of a 355-nm UV wavelength for 10 ps. The laser parameters studied were pulse repetition rate, laser irradiation method, and laser power condition. Previous studies using polyethylene terephthalate (PET), which does not exhibit linear absorption at a UV wavelength, have focused on processing trends resulting in minimal collateral damage around the laser-induced ablation. However, our results showed a trend of accumulating such damage irrespective of the laser parameters. Meanwhile, polyimide (PI) exhibited a completely different behavior depending on the laser parameters. At low pulse repetition rates, minimal collateral damage was observed, whereas at high repetition rates, the morphology varied considerably. The electrical characteristics of the laser-processed materials were found to be correlated with the variations in morphology. In the case of PI, such variations in electrical resistance and morphology indicated that the material was carbonized. The findings of this study are expected to provide a useful reference when selecting parameters for the laser processing of similar polymer materials.
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