Effect of ALD reactants on blistering of aluminum oxide films on crystalline silicon

Atomic layer deposited aluminum oxide (Al₂O₃) has in recent years proven to be a promising surface passivation material for crystalline silicon solar cells. However, blistering in Al₂O₃ films is a common problem deteriorating the surface passivation quality. Here, blistering is studied from material aspects including film thickness, film composition and postdeposition heat treatment. We show how thicker films, higher annealing temperatures and longer annealing times lead to more severe blistering and demonstrate how blistering can be avoided by using either O₃ as the oxidant or depositing a thin TiO₂ layer at the silicon interface.