Enhanced Visible Photovoltaic Response of TiO₂ Thin Film with an All-Inorganic Donor–Acceptor Type Polyoxometalate

In the field of material chemistry, it is of great significance to develop abundant and sustainable materials for solar energy harvesting and management. Herein, after evaluating the energy band characteristics of 13 kinds of polyoxometalates (POMs), the trisubstituted POM compound K₆H₄[α-SiW₉O₃₇Co₃(H₂O)₃]·17H₂O (SiW₉Co₃) was first studied due to its relatively smaller band gap (2.23 eV) and higher lowest unoccupied molecular orbital (LUMO) level (−0.63 V vs NHE). Additionally, the preliminary computational modeling indicated that SiW₉Co₃ exhibited the donor–acceptor (D–A) structure, in which the cobalt oxygen clusters and tungsten skeletons act as the electron donor and electron acceptor, respectively. By employing SiW₉Co₃ to modify the TiO₂ film, the visible photovoltaic and photocurrent response were both enhanced, and the light-induced photocurrent at 420 nm was improved by 7.1 times. Moreover, the highly dispersive and small sized SiW₉Co₃ nanoclusters loading on TiO₂ were successfully achieved by fabricating the nanocomposite film of {TiO₂/SiW₉Co₃}₃ with the layer-by-layer method, which can result in the photovoltaic performance enhancement of dye-sensitized solar cells (DSSCs), of which the overall power conversion efficiency was improved by 25.6% from 6.79% to 8.53% through the synergistic effect of POMs and Ru-complex.