Type-II core/shell CdTe/CdS quantum dots (QDs) are assembled onto TiO₂ nanotube array (NTA) films using a bi-functional linker molecule with the help of a hydrothermal method coupled with successive ionic layer adsorption and reaction process. Spatial separation of the electron and hole wave functions within the core/shell heterostructured nanocrystals appears to result in an extended charge separation state, resulting in a significant increase in photocurrent and excellent device stability. When only CdS or CdTe QDs are used as the sensitizer, the largest photocurrent densities are 1.31 mA cm⁻² and 1.23 mA cm⁻², respectively. For the core/shell CdTe/CdS QDs sensitized TiO₂ NTA photoelectrodes the photocurrent density increases to ≈9.17 mA cm⁻², dramatically larger than the values obtained with only one sensitizer. The core/shell CdTe/CdS QDs sensitized TiO₂ NTA photoelectrodes provide a remarkable photoelectrochemical cell efficiency of 6.12%. To the best of our knowledge this photoconversion efficiency is the highest in the field of QD-sensitized photoelectrodes. A corresponding hydrogen evolution rate as high as 1560 μmol h⁻¹ W⁻¹ was achieved.