Synthesis, crystal structure, DFT, and photovoltaic studies of BaCeCuS3

We report the synthesis of single crystals of the quaternary sulfide, BaCeCuS3, for the first time by heating a polycrystalline sample of BaCeCuS3 with an excess of KCl flux inside a vacuum-sealed fused silica tube. The crystal structure of the compound is determined by a single-crystal X-ray diffraction study which shows that it crystallizes in the primitive orthorhombic crystal system (space group: Pnma) with cell constants of a = 10.6740(13) angstrom, b = 4.1200(6) angstrom, and c = 13.409(2) angstrom. The structure is best described as a pseudo-two-dimensional structure where tetrahedral CuS4 and octahedral CeS6 units serve as the main building blocks. The polyanionic (infinity)(2)[CeCuS3](2) layers in the structure are separated by the presence of electropositive Ba2+ cations. The optical absorption study on the polycrystalline sample of BaCeCuS3 shows a semiconducting nature with a direct bandgap of 1.8(2) eV consistent with the green color of the sample. The temperature-dependent thermal conductivity (k(tot)) measurements on the polycrystalline BaCeCuS3 sample reveal an extremely low value of k(tot) (0.32 W m(-1) K-1) at 773 K. DFT calculations were carried out to obtain the electronic structure of the title compound. Our theoretical studies predict a high value of the thermoelectric figure of merit (> 1) for BaCeCuS3 by optimization of the charge carriers. To also explore a practical application of BaCeCuS3, a liquid junction solar cell was fabricated: TiO2/CdS/BaCeCuS3/S-n(2-)/S2-/MWCNTs@Ni, and the cell delivered an efficiency enhanced by & SIM;45% compared to the one without the sulfide. The performance improvement is affected by the hole conducting properties of BaCeCuS3, which allows facile hole transfer from CdS to the polysulfide, increases the charge separation, and hence increases the efficiency.

Automated summary

We synthesized single crystals of the quaternary sulfide BaCeCuS3 for the first time by heating a polycrystalline sample with KCl flux in a vacuum-sealed fused silica tube. The crystal structure was determined to be orthorhombic with tetrahedral CuS4 and octahedral CeS6 units serving as the main building blocks. Optical absorption studies showed a direct bandgap of 1.8 eV, consistent with the green color of the sample. Thermal conductivity measurements revealed an extremely low value at high temperatures. DFT calculations predicted a high thermoelectric figure of merit, and a liquid junction solar cell fabricated with BaCeCuS3 showed improved efficiency compared to a cell without the sulfide due to its hole conducting properties.