Amal BaQais1 2 Antton Curutchet3 Ahmed Ziani1 Hassan Ait Ahsaine1 Philippe Sautet4 5 Kazuhiro Takanabe1 Tangui Le Bahers3

1, King Abdullah University of Science and Technology (KAUST), Thuwal, , Saudi Arabia
2, Princess Nourah bint Abdulrahman University (PNU), Riyadh, , Saudi Arabia
3, Universite Lyon, ENS de Lyon, CNRS, Universite Claude Bernard Lyon 1, Lyon, , France
4, University of California, Los Angeles, California, United States
5, University of California, Los Angeles, California, United States

Solar energy is an abundant, clean and free access resource, but it require harvesting and storage for sustainable future. Photovoltaics or photocatalysis technologies dedicated to sun light conversions frequently involve photo-visible-responsive semiconductors [1], such us materials with formula BiMOS (M; Cu [2] or Ag). In this study, we applied a strategy of substitution of Cu by Ag to produce a new family of oxysulfide BiAgOS [3]. We were interested to address how the total substitution of Cu by Ag in BiCuOS system affect its crystal structure, optical and electronic properties by using experimental characterizations and theoretical calculations. Single-phase bismuth silver oxysulfide BiAgOS was prepared by a hydrothermal method. Its structural, morphological, and optoelectronic properties were investigated and compared with those of BiCuOS. Rietveld refinement of the powder X-ray diffraction confirmed that BiAgOS has the same crystal structure as BiCuOS. The diffraction peak positions of BiAgOS, relative to those of BiCuOS, are shifted toward lower angles, indicating an increase in the cell parameters. Combined with experimental measurements, density functional theory calculations employing the range-separated hybrid HSE06 exchange-correlation functional with spin–orbit coupling quantitatively elucidated photophysical properties such as absorption coefficients, effective masses, and dielectric constants. BiCuOS and BiAgOS were found to have indirect bandgaps of 1.1 and 1.5 eV, respectively. The difference in the bandgap results from the difference in the valence band compositions. The hybrid level of the S and Ag orbitals is located at a more positive potential than that of S and Cu leads to widening band gap. Both materials possess high dielectric constants and low electron and hole effective masses. BiAgOS has dielectric constant larger than BiCuOS making it very interesting for photoconversion applications because the material could efficiently screen photogenerated charges. By combining the UV-Vis, Mott-Schottky, and photoelectron spectroscopy in air measurements, the relatively low bandgap of and their p-type character, BiCuOS and BiAgOS can be considered as interesting starting compositions for the development of new semiconductors for photovoltaics or Z-scheme photocatalytic applications. Moreover, this study opened the window toward new oxychalcogenides materials BiAgOCh (Ch; Se, Te) which are not yet synthesis or investigate.

[1] P. Hoffmann, Tomorrow’s Energy; MIT Press: Cambridge, MA, 701, 2004; Vol. 1.
[2] W.C. Sheets, et al., Inorg. Chem., 2007, 46, 10741.
[3] A. BaQais, et al., Chem. Mater., 2017, 29 (20), 8679.