Stability of the surface passivation properties of atomic layer deposited aluminum oxide in damp heat conditions

Surface passivation layers that are stable in the long term are becoming increasingly important in emerging architectures of crystalline silicon photovoltaics. In this work, we study the effect of elevated temperature and humidity on the surface passivation properties of 5 nm to 20 nm thick aluminum oxide (AlOx) layers grown using thermal Atomic Layer Deposition (ALD). ALD-coated p-type Float Zone (FZ) wafers were exposed to 40°C and 85°C in 85% relative humidity (RH), and the passivation properties of the AlOx films were monitored during the damp heat exposure at designated intervals by photoluminescence (PL) imaging. Additionally, minority charge-carrier lifetime, film charge, and interface defect density were measured before and after the exposure. The results indicated that even 5 nm AlOx layers were stable under the prolonged damp heat exposure, and that 20 nm thick passivation layers deposited using either water (H2O) or ozone (O3) as the oxidant in the ALD process had no major differences in passivation stability.