Passivation of Optically Black Silicon by Atomic Layer Deposited Al2O3

Abstract

Optically black silicon nanostructures show excellent anti-reflection and light trapping properties minimizing reflection losses to less than 1.6% between 300 – 1100nm. Our light-trapping scheme enables an absorption enhancement factor of ∼10 at the band edge of silicon (1150nm) as compared to a simulated perfect ARC, where the Yablonovitch limit corresponds to a factor of 15. Just recently it was shown that similar wet-chemically black etched silicon surfaces can be exploited to fabricate high efficiency solar cells [1]. Towards the integration of our structures into a solar cell device, the passivation performance of atomic layer deposited thin Al2O3 films is investigated on a variety of black etched structures. The coatings lead to measured surface recombination velocities of less than 13cm/s on bifacially black structured as well as 12cm/s on polished 1 – 5Ωcm p-type Si CZ wafers. Thinner layers promise to be even more effective. This technology will enable high efficiencies on various solar cell concepts.