Many recent studies have demonstrated the potential of utilizing the compositional tunability of solid-solution systems for band engineering and in increasing photocatalytic performance for applications in solar energy conversion. Solid solution phases, such as most notably GaN:ZnO, have been found to drive overall water-splitting under visible-light irradiation, despite the high level of atomic-level disorder that would normally be expected to decrease charge mobility and increase charge recombination. In contrast, tunability of the bandgap sizes, band energies, and increased photocatalytic activities have been found for several systems. Within the mixed-metal oxides, the band energies and bandgap sizes are known to be a sensitive function of the choice of metal cations. Thus, the formation of solid solutions such as Cu5(Ta1-xNbx)11O30 and Na2(Ta1-xNbx)4O11 have been found to represent a promising strategy for controlling band energetics and enhancing their photocatalytic activities under visible-light for the water-splitting half reactions. Density functional theory calculations have been used to probe impact of the underlying atomic-level disorder on their electronic structures and which enables the separation of excited electron-hole pairs and their diffusion to the surfaces at special threshold compositions. These results are analyzed with respect to their bandgap sizes and band energies, and reveal the general underlying driving forces for the increased range of light absorption and for charge separation in solid-solution systems.

Solid-solution semiconductors: Compositional tuning of metal oxides for the capture and conversion of solar energy

2019 Spring National Meeting

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