“…Recently, considerable progress has been achieved on the developments of alternative materials to Pt CE, such as carbon materials, [6][7][8][9] conductive polymers, 10,11 metal alloys, 12,13 and transitional-metal compounds. 14,15 Among them, nickel sulde with a variety of chemical formulas is found to be promising CE material for the I 3 À reduction reaction in DSSCs. [16][17][18][19] For example, the hierarchal Ni 3 S 4 microspheres reported by Yang et al displayed a power conversion efficiency (PCE) of 6.81% under AM1.5G illumination, comparable to that of Pt-based DSSC (6.85%).…”