A highly (211)-oriented CuBi2O4/TiO2 heterojunction with a sharp interface is fabricated via pulsed laser deposition, exhibiting bifunctional (anodic/cathodic) photoelectrochemical properties. This high-quality p–n heterojunction enables a bias-dependent band structure transformation, facilitating efficient water splitting through both oxidation and reduction reactions. Electrical and band structure analyses provide valuable insights into bifunctional photoelectrochemical behavior of p–n heterojunction photoelectrodes.
Although p–n heterojunctions are fundamental components in photovoltaics and energy conversion devices, an internal electric field loss arising from interfacial defects obstructs the investigation of photoelectrochemical properties using p–n oxide heterojunction photoelectrode. Achieving a high-quality p–n oxide heterojunction with a sharp interface provides an ideal platform for controlling internal electric fields without voltage loss due to structural defects. In this work, we fabricated highly (211)-oriented p-CuBi2O4 thin films with sharp interface grown on (110) n-TiO2 single-crystal substrate using pulsed laser deposition. The sharp heterointerface between (211) CuBi2O4 and (110) Nb:TiO2 resulted in the formation of a Schottky barrier with a height of 0.46 eV. This Schottky barrier suggests contributing to a bifunctional response resulting from a distinct bias-dependent band structure transformation, where space charge region occurred. The CuBi2O4/Nb:TiO2 heterostructure photoelectrode exhibited bifunctional (anodic/cathodic) photoelectrochemical properties, which show 47 and −77 µA cm−2 at a potential of 1.23 and 0 V
RHE, respectively. These findings provide valuable insights into the development of high-quality p–n heterojunction photoelectrodes for advanced bifunctional energy conversion technologies.
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