A facile method for the synthesis of CO3S4 core-shell hexagonal nanosheets (NSs) from Co(NO3)(2) and thioacetamide under alkaline conditions in the presence of poly(vinylpyrrolidone) has been demonstrated. At the molar ratios of thioacetamide/Co2+ of 0.26, 0.52, and 2.6, we prepared hollow-, semi-hollow, and non-hollow CO3S4 core-shell hexagonal NSs. We have found that Ostwald ripening occurring at the core/shell interface accounts for the formation of the hollow Co3S4 core-shell NSs, each consisting of a core of 80 +/- 30 nm in diameter and a shell of 25 +/- 5 nm in thickness. Three CdZnSSe nanostructure-sensitized solar cells incorporating CO3S4 NSs provide an average power conversion efficiency of 3.7 +/- 0.1%, showing high electrocatalytic activity of the CO3S4 NSs toward polysulfide electrolyte. (C) 2011 Elsevier B.V. All rights reserved.