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

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.