| 摘要 |
Cobalt polypyridine complexes are interesting alternative redox mediators for large scale manufacturing of dye-sensitized solar cells (DSCs) since they are less aggressive towards metal contacts and absorb less light than iodide/triiodide. Here we have examined the effect of steric properties of triphenylamine-based organic sensitizers and cobalt polypyridine redox mediators on the electron lifetime and overall device performance in DSCs. Matching the steric bulk of the dye and redox mediator was found to minimize recombination and mass transport problems in DSCs employing cobalt redox mediators. Recombination was efficiently slowed down by introducing insulating butoxyl chains on the dye, allowing the use of a cobalt redox mediator with a less steric bulk. The best efficiency of DSCs sensitized with a triphenylamine-based organic dye in combination with cobalt(II/III) tris(2,2'-bipyridyl) match the highest efficiencies obtained so far with iodide-free electrolytes, reaching a 6.3% overall conversion efficiency under AMI.5 condition (1000 Wm-2) and an efficiency of 7.8% at 1/10 of a sun. Organic dyes with high extinction coefficient can thus be used instead of standard ruthenium sensitizers to build thin films DSCs in order to overcome mass transport and recombination limitations associated with the cobalt redox couples. DSCs sensitized with organic dyes employing cobalt redox mediators are promising for low light intensity applications since the efficiency and voltage is high at indoor illumination.
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