  Large surface area applications such as high-efficiency > 26% solar cells
require surface patterning with 1-10 micrometers periodic patterns at high
fidelity over 1-10 cm^2 areas (before up scaling to 1 m^2) to perform at, or
exceed, the Lambertian (ray optics) limit of light trapping. Here we show a
pathway to high-resolution sub-1 micrometer 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 was used to
alleviate the required high surface tracking tolerance for ablation of 0.3-0.8
micrometer diameter holes in ~40 nm alumina Al2O3-mask at high writing speed,
7.5 cm/s; a patterning rate 1 cm^2 per 20 min. The plasma etching protocol was
optimised for a zero-mesa formation of photonic crystal (PhC) trapping
structures and smooth surfaces at the nanoscale level. Scaling up in area and
throughput of the demonstrated approach is outlined.
