Crystal structure design and multiband physical properties of quaternary sulfide Ba5Bi2Co2S10 for optoelectronic conversionElectronic supplementary information (ESI) available. CCDC 1877665. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c9cc00794f

Multiband materials have received increasing attention due to their superior solar absorption properties. Here we design a new multiband compound, namely Ba 5 Bi 2 Co 2 S 10 , which crystallizes in the space group C 2 2h - P 2 1 / m (No. 11) of the monoclinic system. Ba 5 Bi 2 Co 2 S 10 is composed of one-dimensional 1 ∞ [Bi 2 Co 2 S 10 ] 10− chains along the a axis. The adjacent chains are separated by Ba 2+ ions. The optical band gap of the compound is 1.05 eV and 0.74 eV, presenting typical multi-absorption characteristics. First-principles calculations, which are perfectly consistent with the experimental results, show that the hybrid coupling effect between Co and S gives rise to multiband characteristics. Evident optoelectronic conversion properties were observed under visible light illumination with a photocurrent density of 4.0 mA cm −2 at 1 V. Band alignment of hypothetical Bi-M T -S compounds with M T in O h and T d symmetry, respectively. Crystal structure of Ba 5 Bi 2 Co 2 S 10 viewed down the a -axis and multiband properties with optimal bandgap of Ba 5 Bi 2 Co 2 S 10 .