Quantifying the Effect of Nanofeature Size on the Electrical Performance of Black Silicon Emitter by Nanoscale Modeling

Nanostructured black silicon (b-Si) surfaces with an extremely low reflectance are a promising light-trapping solution for silicon solar cells. However, it is challenging to develop a high-efficiency front-junction b-Si solar cell due to the inferior electrical performance of b-Si emitters, which outweighs any optical gain. This article uses three-dimensional numerical nanoscale simulations, which are corroborated with experiment results, to investigate the effect of the surface nanofeature sizes on the b-Si emitter performance in terms of the sheet resistance (${\rm{R_{sheet}}}$) and the saturation current density (${\rm{J_{0e}}}$). We show that the specific surface area (SSA) is an effective parameter to evaluate the nanofeature size. A shallow surface nanofeature with a large SSA will contribute to a better electrical performance. We will show that b-Si emitter ${\rm{R_{sheet}}}$ measured by a four-point probe is not a measure of the doping level in the nanofeature, but is ruled by the doping level in the underlying substrate region. We also show that a small nanofeature with SSA > 100 mu m-1 and height < 100 nm can lead to a relatively low ${\rm{J_{0e}}}$ (33 fA/cm2 lower than the best b-Si results reported in the literature) by suppressing surface minority carrier density and minimizing the total Auger recombination loss.

Automated summary

Nanostructured black silicon surfaces show promise for silicon solar cells. However, developing high-efficiency black silicon solar cells is challenging due to the inferior electrical performance of the black silicon emitters. This article investigates the effect of surface nanofeature sizes on the performance of black silicon emitters.