Non stoichiometric Cu In S@ZnS nanoparticles produced in aqueous solutions as light harvesters for liquid junction photoelectrochemical solar cells
A direct "green" aqueous synthesis of mercapto acetate stabilized copper indium sulfide (CIS) nanoparticles (NPs) and core/shell CIS@ZnS NPs of a varied composition under ambient conditions and a temperature lower than 100 degC is reported. The CIS@ZnS NPs can be anchored to the surface of nanocrystalline FTO/TiO2 films without additional purification or ligand exchange steps yielding visible light sensitive heterostructures ready for using as photoanodes in the liquid junction solar cells. The highest photoelectrochemical activity in a three electrode cell was demonstrated by a TiO2/CIS@ZnS heterostructure with atomic Cu In S and Zn Cu ratios of 1 5 10 and 1 1. The optimized TiO2/CIS@ZnS photoanodes were tested in two electrode solar cells with aqueous polysulfide electrolyte and TiO2/Cu2S heterostructures produced by a photo assisted method as counter electrodes. Under illumination by a 30 mW cm 2 xenon lamp, the optimized cells showed the average light conversion efficiency of 8.15% the average open circuit voltage of 0.6 V and the average fill factor of 0.42. The cells revealed excellent stability and reproducibility of photoelectrochemical parameters with around one percent variation of the light conversion efficiency around an average value for six identical solar cells.