Tantalum oxide/silicon nitride: A negatively charged surface passivation stack for silicon solar cells

This letter reports effective passivation of crystalline silicon (c-Si) surfaces by thermal atomic layer deposited tantalum oxide (Ta2O5) underneath plasma enhanced chemical vapour deposited silicon nitride (SiNx). Cross-sectional transmission electron microscopy imaging shows an approximately 2 nm thick interfacial layer between Ta2O5 and c-Si. Surface recombination velocities as low as 5.0 cm/s and 3.2 cm/s are attained on p-type 0.8 Omega center dot cm and n-type 1.0 Omega center dot cm c-Si wafers, respectively. Recombination current densities of 25 fA/cm(2) and 68 fA/cm(2) are measured on 150 Omega/sq boron-diffused p(+) and 120 Omega/sq phosphorus-diffused n(+) c-Si, respectively. Capacitance-voltage measurements reveal a negative fixed insulator charge density of -1.8 x 10(12) cm(-2) for the Ta2O5 film and -1.0 x 10(12) cm(-2) for the Ta2O5/SiNx stack. The Ta2O5/SiNx stack is demonstrated to be an excellent candidate for surface passivation of high efficiency silicon solar cells. (C) 2015 AIP Publishing LLC.