Unraveling the mechanism underlying the enhanced photoresponse in BiVO4-modified TiO2 nanorod arrays for quasi-solid-state solar cells

Enhancing the visible light response of wide-bandgap semiconductors is crucial for the advancement of oxide-based solar devices. Here, we report a TiO 2 nanorod array (TNRAs)/BiVO 4 heterojunction photoanode fabricated via a cyclic spin-coating strategy, where the number of coating cycles (10, 15 or 20) is used to regulate the deposition of BiVO 4 . The formation of a type-II band alignment facilitated efficient charge separation, while the incorporation of BiVO 4 extended the light absorption from ∼400 nm to ∼500 nm, as confirmed by UV–Vis spectroscopy. Electrochemical impedance spectroscopy revealed reduced charge transfer resistance, and density functional theory (DFT) calculations showed that the bandgap narrowed and visible-light absorption increased with increasing BiVO 4 thickness. The optimized heterojunction (15 deposition cycles) delivers a photocurrent density of 1.41 mA cm - 2 in the quasi-solid-state solar cell ∼19 times that of the pristine TNRAs (0.075 mA cm - 2 ) with a power conversion efficiency of 0.277%. The device also exhibits remarkable photocurrent stability in the quasi solid electrolyte (QSE). This study elucidates the interplay between heterointerface structure and optoelectronic performance and offers a scalable route to engineering stable, high-efficiency, oxide-based solar energy systems.