Mitsuhiro Kusaba

Abstract The surface morphology of silicon solar cells irradiated with KrF excimer laser pulses (λ = 248 nm, τ = 20 ns) was investigated below the experimentally observed melting threshold fluence (F _th) of 0.47 J cm⁻² (±20%). At laser fluences of 0.23–0.48 J cm⁻² (equivalent to 0.49F _th to 1.0F _th), nanodot structures with a height and width of approximately 60–120 nm were periodically formed with an interdot spacing similar to the laser wavelength. The observed nanodot density (29 dots μm²) was higher than that previously obtained at longer wavelengths. Furthermore, crystallinity analysis by micro-Raman spectroscopy revealed a Raman shift of 519.56 cm⁻¹ after irradiation (N= 1500 pulses), compared with 518.27 cm⁻¹ prior to irradiation. A laser fluence of 0.41 J cm⁻² ( = 0.87F _th) was found to induce compressive stress on the silicon solar cell surface.

A tungsten carbide-cobalt (WC-Co) composite layer was formed on a stainless-steel type 304 (SS304) substrate using multibeam laser metal deposition (LMD) with blue diode lasers. This paper aims to provide WC-Co layer formation with low porosity and high layer formation efficiency by using the multibeam LMD process. The effects of process parameters such as laser output power and powder feed rate are tied together to explain the geometry of the melt layer as well as the fraction of the laser energy used for melting a material. The experimental results show that the porosity rate and layer formation efficiency were recorded at 0.3% and 0.0042 mm3/J, respectively, at the laser output power of 180 W and a powder feed rate of 75 mg/s. It was revealed that layer formation efficiency was dependent on the laser output power.

The Perpendicular Period and Phase Scanning (P³S) method can evaluate the uniformity of a laser-induced periodic surface structure (LIPSS). P³S assesses the uniformity of LIPSS using the standard deviation of the peak period and the average of the phase difference in the direction perpendicular to LIPSS. The P³S method demonstrates that LIPSS formed by two-color double-pulse irradiation is reduced to a quarter of the period dispersion, and the average phase difference of LIPSS is also reduced compared to the single-pulse irradiation. In addition, a 3D electromagnetic particle-in-cell simulation was performed to evaluate the possibility of an improved uniformity of LIPSS. The results confirm that the two-color double-pulse irradiation produces a uniform LIPSS and validates the effectiveness of the P³S method to assess the uniformity of LIPSS.