Passivation interlayers such as Al 2 O 3 are required to improve the hole selectivity of dopant-free passivating contact based on transition metal oxides. For the interlayer to provide low surface recombination as in conventional silicon heterojunctions (SHJs) or tunnel oxide passivated contact (TOPCon) technologies, "hydrogenation" strategies to effectively introduce hydrogen in passivation interlayers while being compatible with transition metal oxides (TMOs) are urgently sought after. In this work, an easy-to-implement strategy to successfully incorporate extra hydrogen in the Al 2 O 3 passivation layer is developed. The chemical and field-effect passivation mechanisms of the extra hydrogen are revealed via comprehensive experimental analyses and density functional theory calculations. By implementing H-Al 2 O 3 with Cu 2 O as the hole-selective rear contact in p-type crystalline silicon (c-Si) solar cells, a remarkable efficiency of 20.35% is achieved (fill factor of 84.76%). The study highlights a promising approach to improve the passivation quality of dielectric interlayers and boost the performance of dopant-free c-Si solar cells to compete against mainstream c-Si photovoltaics technologies.