Bessel-Beam Direct Write of the Etch Mask in a Nano-Film of Alumina for High-Efficiency Si Solar Cells

Abstract

Large surface area applications such as high efficiency >26% solar cells require surface patterning with 1–10 μm periodic patterns at high fidelity over (Formula presented.) areas (before up scaling to (Formula presented.)) to perform at, or exceed, the Lambertian (ray optics) limit of light trapping. Herein, a pathway is shown to high-resolution sub-1 μm etch mask patterning by ablation using direct femtosecond laser writing performed at room conditions (without the need for a vacuum-based lithography approach). A Bessel beam is used to alleviate the required high surface tracking tolerance for ablation of 0.3–0.8 μm diameter holes in 40 nm alumina (Formula presented.) –mask at high writing speed, 7.5 cm s−1; a patterning rate 1 cm2 per 20 min. Plasma etching protocol was optimized for a zero-mesa formation of photonic-crystal-trapping structures and smooth surfaces at the nanoscale level. The maximum of minority carrier recombination time of 2.9 ms was achieved after the standard wafer passivation etch; resistivity of the wafer was 3.5 Ω cm. Scaling up in area and throughput of the demonstrated approach is outlined.