Ultrathin (∼1 nm) films have been widely used for high-efficiency crystalline silicon (c-Si) solar cells such as tunnel oxide passivated contact (TOPCon) solar cells. In this article, we present our recent results for the applications of ultrathin silicon oxide (SiOx) and silicon nitride (SiNx) films to c-Si solar cells. The following topics are reviewed. 1) Ultrathin SiNx can be utilized for passivating contacts instead of SiOx in the TOPCon structure. 2) The addition of SiOx between c-Si and thick catalytic-chemical-vapor-deposited (Cat-CVD) SiNx significantly improves the quality of surface passivation. 3) Ultrathin Al-doped SiOx films formed just by dipping in Al(NO3)3 solution on c-Si provide strong upward band bending due to negative fixed charges, which can be used for hole-selective contacts.