Epitaxial Self‐Assembled Vertically Aligned Nanocomposite Photoelectrodes with Tunable Ambipolar Response

Abstract

Abstract Photocurrent polarity switching in semiconductor photoelectrodes enables the development of optoelectronic switches and logic devices driven by illumination and applied potential. Here, a new class of ambipolar photoelectrodes that display controlled photoelectrochemical photocurrent switching (PEPS) behavior, based on epitaxial self‐assembled vertically aligned NiTiO 3 –TiO 2 nanocomposite thin films synthesized via pulsed laser deposition (PLD) is reported. Phase‐pure NiTiO 3 and TiO 2 films are grown under optimized deposition conditions, while mixed‐phase nanocomposites are engineered by adjusting the Ni/Ti ratio of the ablated targets. Structural characterization confirms the formation of vertically aligned epitaxial rutile TiO 2 nanocolumns within the NiTiO 3 matrix at high Ni/Ti ratios, and NiTiO 3 nanocolumns within the TiO 2 matrix at low Ni/Ti ratios. Photoelectrochemical (PEC) measurements reveal ambipolar behavior with a composition‐dependent crossover potential between anodic and cathodic photocurrents tunable over a range of 800 mV. Phase‐pure NiTiO 3 exhibits intrinsic photocurrent switching, whereas TiO 2 maintains a stable photoanodic response. The introduction of NiTiO 3 into TiO 2 substantially disrupts photoanodic performance, while TiO 2 incorporation into NiTiO 3 enhances photoanodic photocurrent without significantly affecting photocathodic activity. These findings establish vertically aligned nanocomposites (VANs) as a new platform for switchable photoelectrodes and provide new insights into the role of mixed‐phase oxide structures in PEC logic devices and optoelectronic switching applications.