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

摘要

This letter reports effective passivation of crystalline silicon (c-Si) surfaces by thermal atomic layer deposited tantalum oxide (Ta_2O_5) underneath plasma enhanced chemical vapour deposited silicon nitride (SiN_x). Cross-sectional transmission electron microscopy imaging shows an approximately 2 nm thick interfacial layer between Ta_2O_5 and c-Si. Surface recombination velocities as low as 5.0cm/s and 3.2cm/s are attained on p-type 0.8 Ω·cm and n-type 1.0 Ω·cm c-Si wafers, respectively. Recombination current densities of 25 fA/cm~2 and 68 fA/cm~2 are measured on 150Ω/sq boron-diffused p~+ and 120Ω/sq phosphorus-diffused n~+ c-Si, respectively. Capacitance-voltage measurements reveal a negative fixed insulator charge density of -1.8 × 10~(12)cm~2 for the Ta_2O_5 film and - 1.0 × 10~(12)cm~(-2) for the Ta_2O_5/SiN_x stack. The Ta_2O_5/SiN_x stack is demonstrated to be an excellent candidate for surface passivation of high efficiency silicon solar cells.