Optimised antireflection coatings using silicon nitride on textured silicon surfaces based on measurements and multidimensional modelling

Abstract

Plasma-deposited silicon nitride (a-SiN x:H, or briefly, SiNx) is currently the state-of-the-art antireflection coating for silicon wafer solar cells. It simultaneously reduces front-side optical reflection and provides surface and bulk passivation. Silicon nitride films with higher refractive index typically provide a higher level of crystalline silicon surface passivation in the as-deposited state, but the resulting solar cells suffer from a degraded blue response as the films become more absorbing. Hence, it is important to consider all loss mechanisms while optimising SiNx antireflection coatings for silicon wafer solar cells. In this work, the refractive index (n) of the SiNx films is varied from 1.9 to 2.7. The reflection and absorption losses of textured Si wafers coated with various SiNx films are quantified using 2D modelling. It is shown that SiNx films with n = 2.0 (at λ = 633.3 nm) and thickness of 70 nm provide a weighted average reflectance (WAR 1000) of less than 2.5 % and a weighted average transmission (WAT 1000) of more than 97 % on textured mono-Si wafers, combined with a very low saturation current density of 100 fA/cm on 70 Ω/sq n + layers. This shows that very good optical and excellent surface passivation quality can be realised on textured silicon wafers using inline deposited plasma silicon nitride. © 2011 Published by Elsevier Ltd.