In this manuscript we study the surface passivation properties of ultrathin Al2O3 in silicon heterojunctions. The Al2O3 layer needs to be thin enough (<1.2nm) to enable carrier collection through the passivation layer. Previous work on Al2O3 shows that thicknesses below 10nm do not provide adequate surface passivation. In this work, we combine 0.8 nm of Al2O3 with 1nm of SiO2 to improve the passivation properties of the thin Al2O3. The SiO2 helps to improve the chemical passivation by increasing the storage capacity of hydrogen with Al2O3, and the overall negative fixed charge of the SiO2/Al2O3 stack. Additionally, we have optimized the rapid thermal annealing in forming gas environment to activate the Al2O3 in the SiO2/Al2O3 stack. To further increase the hydrogen in the films we deposited n-a-Si:H film before the annealing step. Effective minority-carrier lifetimes of 5 ms and implied open-circuit voltages of 723 mV were accomplished.