CdIn₂S₄ chalcogenide/TiO₂ nanorod heterostructured photoanode: An advanced material for photoelectrochemical applications

A highly three-dimensional CdIn₂S₄ deposited TiO₂ (CdIS/TONR/FTO) heterostructured photoanode has been fabricated via a two-step hydrothermal process to enhance the photoelectrochemical (PEC) performance. In this work, bare TiO₂ nanorods are grown successfully on the fluorine-doped tin oxide (FTO) substrate via a hydrothermal method (TONR/FTO), and a second-step hydrothermal synthesis is used to grow CdIn₂S₄ flower nanostructured layer over the top surface of the bare TONR/FTO. Structural, morphological, optical, and elemental analysis of CdIS/TONR/FTO heterostructure photoanode is investigated in detail. PEC performances are studied in 0.2 V versus Ag/AgCl in mixed sulfide-based electrolyte for various concentrations of CdIn₂S₄ deposited on photoanodes. The photocurrent density for optimized (×4)-CdIS/TONR/FTO heterostructure photoanode is observed to be three times higher than that of the bare TONR/FTO photoanode. This excellent PEC performance is ascribed to the way that the deposited CdIn₂S₄ layer and TiO₂ nanorods synergistically allow the absorption of a wide portion of the solar spectrum under back illumination, and provide efficient separation of the electron-hole pairs in the photoanode architecture. The EIS and IMPS analysis also reveal the significance of CdIn₂S₄ layer that provides the lowest charge-transfer resistance at the interface and high electron-transfer rate in CdIS/TONR/FTO photoanode. Mainly, the deposited CdIn₂S₄ layer significantly broadens the optical absorption capacity, and provides efficient electrons-holes transfer that reduces the recombination losses of the charge carriers. The proposed charge transfer mechanism in CdIS/TONR/FTO heterojunction is well studied.