Sn-Based Perovskite with a Wide Visible-Light Absorption Band Assisted by Hydride Doping

Visible-light-absorbing, narrow-gap semiconductors have attracted significant interest in recent years owing to their photofunctional applications, including heterogeneous photocatalysis and solar cells. Herein, we report a new Pb-free perovskite material with a wide range of visible-light absorption that was successfully synthesized via hydride (H–)-ion doping into BaSn0.7Y0.3O3−δ. Chemical reduction that accompanied H–-ion doping significantly reduced the optical band gap of the host BaSn0.7Y0.3O3−δ from 4.0 to 2.0 eV. Physicochemical measurements revealed that BaSn0.7Y0.3O3−δ underwent the partial reduction of Sn4+ to Sn2+ at B-sites while maintaining the cubic perovskite structure. Density functional theory calculations showed that the electronic states derived from the Sn2+ lone pair, which was located above the top of the valence band, contributed to the visible-light absorption of reduced BaSn0.7Y0.3O3−δ. The prior introduction of oxygen defects into BaSnO3 by Y3+ substitution for Sn4+ was also indispensable to realize a significant reduction of the band gap. The reduced BaSn0.7Y0.3O3−δ doped with H– ions was applied as a photoelectrode material, and a clear anodic photoresponse of up to 600 nm was observed, which demonstrates that the material can be used for photofunctional applications. The results of this work suggest that the utilization of stereoactive lone pair of electrons in combination with H– doping may provide another approach to the band gap reduction of Sn(IV)-based oxides, which are nontoxic and less expensive, but generally wide-gap semiconductors.