Formation of large area light trapping patterns for Si solar cells

Current trend of the average laser power increase follows Moore's law. The average power of ultra-short lasers in 2000 was 1 W and now is 1 kW following trend of doubling per year: 2^(20years/2) = 1024. This trend can be harnessed for large area patterning. Here we show application of direct laser writing for processing of surface of solar cells. Light trapping photonic crystal (PhC) patterns on the surface of Si solar cells provides a novel opportunity to approach the theoretical efficiency limit of 32.3% for light-to-electrical power conversion with a single junction cell. This is beyond the efficiency limit implied by the Lambertian limit of ray trapping ~29%. The interference and slow light effects are harnessed for collecting light even at the long wavelengths near the Si band-gap. We compare two different methods for surface patterning, that can be extended to large area surface patterning: 1) laser direct write and 2) step-&-repeat 5-times reduction projection lithography.