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

Large surface area applications such as high efficiency >26% solar cells require surface patterning with 1–10 μm periodic patterns at high fidelity over areas (before up scaling to ) 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 –mask at high writing speed, 7.5 cm s −1 ; a patterning rate 1 cm 2 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.