AbstractTi³⁺ species are highly unstable in air owing to their facile oxidation into Ti⁴⁺ species, and thus they cannot concentrate in the surface layer of TiO₂ but are mainly present in its bulk. We report generation of abundant and stable Ti³⁺ species in the surface layer of TiO₂ by boron doping for efficient utilization of solar irradiation. The resultant photocatalysts (denoted as B-TiO_2−x) exhibit extremely high and stable solar-driven photocatalytic activity toward hydrogen production. The origin of the solar-light activity enhancement in the B-TiO_2−x photocatalysts has been thoroughly investigated by various experimental techniques and density functional theory (DFT) calculations. The unique structure invoked by presence of sufficient interstitial boron atoms can lead to substantial variations in density of states of B-TiO_2−x, which not only significantly narrow the band gap of TiO₂ to improve its visible-light absorption, but also promote the photogenerated electron mobility to enhance its solar-light photocatalytic activity.