Defect‐Enhanced Charge Separation and Transfer within Protection Layer/Semiconductor Structure of Photoanodes

Silicon (Si) requires a protection layer to maintain stable and long‐time photoanodic reaction. However, poor charge separation and transfer are key constraint factors in protection layer/Si photoanodes that reduce their water‐splitting efficiency. Here, a simultaneous enhancement of charge separation and transfer in Nb‐doped NiOx/Ni/black‐Si photoanodes induced by plasma treatment is reported. The optimized photoanodes yield the highest charge‐separation efficiency (ηsep) of ≈81% at 1.23 V versus reversible hydrogen electrode, corresponding to the photocurrent density of ≈29.1 mA cm−2. On the basis of detailed characterizations, the concentration and species of oxygen defects in the NiOx‐based layer are adjusted by synergistic effect of Nb doping and plasma treatment, which are the dominating factors for forming suitable band structure and providing a favorable hole‐migration channel. This work elucidates the important role of oxygen defects on charge separation and transfer in the protection layer/Si‐based photoelectrochemical systems and is encouraging for application of this synergistic strategy to other candidate photoanodes. A NiOx/black Si photoanode with efficient charge separation and transfer is successfully fabricated via a synergistic effect of Nb doping and plasma treatment. The oxygen defects tuned by the synergistic effect are the dominating factors for forming a suitable band structure and providing favorable hole‐migration channel. This intriguing strategy may pave the way for further advancing the performance in photoelectrodes.