Study on annealing process of aluminum oxide passivation layer for perc solar cells

In this study, Atomic Layer Deposition (ALD) equipment was used to deposit Al₂O₃ film on a p-type silicon wafer, trimethylaluminum (TMA) and H₂O were used as precursor materials, and then the post-annealing process was conducted under atmospheric pressure. The Al₂O₃ films annealed at different temperatures between 200–500^◦C were compared to ascertain the effect of passivation films and to confirm the changes in film structure and thickness before and after annealing through TEM images. Furthermore, the negative fixed charge and interface defect density were analyzed using the C-V measurement method. Photo-induced carrier generation was used to measure the effective minority carrier lifetime, the implied open-circuit voltage, and the effective surface recombination velocity of the film. The carrier lifetime was found to be the longest (2181.7 µs) for Al₂O₃/Si post-annealed at 400^◦C. Finally, with the use of VHF (40.68 MHz) plasma-enhanced chemical vapor deposition (PECVD) equipment, a silicon nitride (SiN_x) film was plated as an antireflection layer over the front side of the wafer and as a capping layer on the back to realize a passivated emitter and rear contact (PERC) solar cell with optimal efficiency up to 21.54%.