Sulfide Modification of Dye-Sensitized Solar Cell Gold Cathodes for Use with Cobalt Polypyridyl Mediators

Abstract

[Co(bpy)3]2+/3+-type complexes have emerged as promising alternatives to the traditional I–/I3– electrolyte used in dye-sensitized solar cells (DSSCs). One of the many advantages these complexes exhibit is their ability to undergo reduction on Au cathodes rather than the more expensive Pt. However, in our experience irreproducibility of fabricated Au cathodes has been a longstanding issue due to variations in charge-transfer resistance (RCT) for the Co2+/3+ couple. These variations manifest themselves as poor fill factors in the current–voltage measurements. In an effort to increase electronic coupling between the Co complex and the Au surface (and thereby reduce RCT), a simple surface modification with sulfide ion has been developed. XPS measurements indicate the modification is stable after exposure to mediator solution. Cyclic voltammetry shows a drastic increase in reversibility for the Co2+/3+ electrochemistry, especially under typical DSSC mediator conditions. A commensurate enhancement in the fill factor is observed in subsequent J–V measurements. The results provide a straightforward method of yielding more reproducible Au cathodes to be used in combination with [Co(bpy)3]2+/3+-type mediators.