One-dimensional photogeneration profiles in silicon solar cells with pyramidal texture

The key metric of surface texturing is the short-circuit current J _sc. It depends on front surface transmittance, light trapping and the spatial profiles of photogeneration G and collection efficiency _c. To take advantage of a one-dimensional profile of _c(ζ), where ζ is the shortest distance to the p-n junction, we determine G(ζ) via ray tracing. This permits rigorous optical assessment of common pyramidal textures for various cell designs. When ζ is small, G(ζ) is largest beneath regular inverted pyramids, upright pyramids (regular or random) and planar surfaces, respectively. This higher G(ζ) results in superior collection of generated carriers in front-junction cells. In simulations of a conventional screen-print cell, 92.0% of generated carriers are collected for inverted pyramids, compared to 91.4% for upright pyramids, and 90.0% for a planar surface. Higher efficiency and rear junction devices are analysed in the paper. Despite differences in G(ζ) beneath textures, inverted pyramids achieve the highest J _sc for all cell designs examined (marginally so for high-efficiency rear-contact cells) due to superior front surface transmittance and light trapping. We assess a common one-dimensional model for photogeneration beneath textured surfaces. This model underestimates G(ζ) when ζ is small, and overestimates G(ζ) when ζ is large. As a result, the generation current determined is inaccurate for thin substrates. It can be computed to within 3% error for 250 μm thick substrates. However, errors in G(ζ) can lead to 7.5% inaccuracy in calculations of J _sc. Errors are largest for lower efficiency designs, in which collection efficiency varies through the substrate.