Hydrogenation of p+ poly-Si by Al2O3 nanolayers prepared by atomic layer deposition

Abstract

Polysilicon (poly-Si) passivating contacts have enabled some of the highest lab-scale crystalline silicon (c-Si) solar cell conversion efficiencies, largely due to their excellent surface passivation quality, which can be aided by means of hydrogenation treatments. One frequently applied method is to use hydrogen-rich capping layers, such as Al2O3 or SiNx, which can provide hydrogen to the poly-Si/SiOx/Si interface upon annealing. In this work, the effect of the deposition conditions of the Al2O3 layers, fabricated by various types of atomic layer deposition (ALD), on the hydrogenation of p+ poly-Si is investigated, and it is compared to the direct passivation of c-Si by the same Al2O3 layers. It is found that excellent hydrogenation of the p+ poly-Si by Al2O3 could be reached by a wide range of ALD conditions, but higher annealing temperatures were required as compared to passivation of c-Si. The different ALD conditions result in Al2O3 layers with varying refractive indices, O/Al ratios, and hydrogen content, although these material properties become highly similar upon annealing. Furthermore, the p+ poly-Si layer appears to act as a reservoir for hydrogen, which alters the hydrogen effusion profiles of the Al2O3 layers. The results show that a wide range of Al2O3 layers are highly suitable for hydrogenation of p+ poly-Si and provide more insight into the hydrogenation process of poly-Si passivating contacts.