Efficiency improvement of PERC solar cell using an aluminum oxide passivation layer prepared via spatial atomic layer deposition and post-annealing

Abstract In this study, Al 2 O 3 thin films are deposited on p-type silicon using spatial atomic layer deposition with trimethylaluminum and H 2 O. The films are annealed in atmosphere (ATM), forming gas (FG) and nitrogen (N 2 ) at temperatures of 300–750 °C. Effects of annealing gas ambient and temperature on structural, electrical, and passivation properties of Al 2 O 3 /Si are systematically investigated. The experimental results show that the ATM annealing leads to an interfacial silicon oxide more than two times thicker than that of the samples annealed in FG and N 2 . The ratio of tetrahedral AlO 4 to octahedral AlO 6 can be correlated to the negative fixed oxide charge density (Q f ) near the interface of Al 2 O 3 /Si. The 600 °C ATM-annealed sample has the highest Q f of 3.23 × 10 12  cm −1 and thus gives the best field effect passivation. The sample annealed in FG at 450 °C has the lowest interface trap density (D it ) of 3.98 × 10 11  eV −1  cm −2 , indicating that the hydrogen is more effective than oxygen for chemical passivation. Overall, the FG-annealed sample has the highest lifetime of 933.8 μs, showing that chemical passivation is the primary consideration. The ATM annealing requires higher temperatures (~600 °C) to reach the optimal passivation, whereas the FG and N 2 annealing temperature is limited to 450 °C to avoid dehydrogenation. Finally, for passivated emitter and rear contact cell fabrication, the cell with FG annealing has the best conversion efficiency of 21.43%, which is 0.17 and 0.54 percentage point higher than that of the cells with ATM and N 2 annealing, respectively.