Regulating the Silicon/Hematite Microwire Photoanode by the Conformal Al₂O₃ Intermediate Layer for Water Splitting

Dual-absorber photoelectrodes have been proved to possess greater potential than the single-absorber systems in the applications of photoelectrochemical (PEC) cells (e.g., solar-driven water splitting); however, the mismatching of the energy bands and substantial carrier recombinations at the two absorber interfaces are normally subsistent. Here, we introduce an intermediate layer of conformal Al₂O₃ into the silicon/hematite (Si/α-Fe₂O₃) microwire photoanode for enriching the understanding of the interaction among the interlayer, inner absorber, and outer absorber. Our results show that the Si/Al₂O₃/α-Fe₂O₃ microwire photoanode with the thickness-optimized Al₂O₃ can lead to a substantial increase in the photocurrent from 0.83 to 2.08 mA/cm² at 1.23 V_RHE (under 1 sun irradiation) and an obvious decrease in the onset potential relative to the counterpart without Al₂O₃. By analyzing the PEC responses under various monochromatic lights, PEC impedance spectroscopy, and intensity-modulated photocurrent spectroscopy, we ascribe the improvements to the fact that the suitable-thickness Al₂O₃ can passivate the Si microwire surfaces and the bottom surfaces of the α-Fe₂O₃ film and give rise to Al doping into the post-synthesized α-Fe₂O₃. These essential causes promote the carrier separation in α-Fe₂O₃, diminish the photoanode surface recombination rate, and then increase the surface charge-transfer efficiency.