Preparation of highly electroactive cobalt sulfide core–shell nanosheets as counter electrodes for CdZnSSe nanostructure-sensitized solar cells

Abstract A facile method for the synthesis of Co 3 S 4 core–shell hexagonal nanosheets (NSs) from Co(NO 3 ) 2 and thioacetamide under alkaline conditions in the presence of poly(vinylpyrrolidone) has been demonstrated. At the molar ratios of thioacetamide/Co 2+ of 0.26, 0.52, and 2.6, we prepared hollow-, semi-hollow, and non-hollow Co 3 S 4 core–shell hexagonal NSs. We have found that Ostwald ripening occurring at the core/shell interface accounts for the formation of the hollow Co 3 S 4 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 Co 3 S 4 NSs provide an average power conversion efficiency of 3.7±0.1%, showing high electrocatalytic activity of the Co 3 S 4 NSs toward polysulfide electrolyte.