Efficient copper mediators based on bulky asymmetric phenanthrolines for DSSCs

In the context of the development of new electron mediators for dye-sensitized solar cells that could efficiently substitute the more common I3−/I− redox couple, we have prepared a series of Cu(I)- phenanthroline complexes through an easy synthetic route. The novel [Cu(2-mesityl-4,7-dimethyl-1,10-phenanthroline)2]PF6 (3) is of particular interest because the presence of the bulky mesityl groups protects as a kiss lock the Cu center, leading to superior dye regeneration kinetics with respect to simpler phenanthrolinebased Cu(I) complexes and to a lower dark current with respect the I3−/I−. The exploitation of a dual-component electrolyte constituted by (3) and a Fe(II) comediator, in combination with the [Ru(4,4′-dicarboxy-2,2′- bipyridine)2(4,4′-dinonyl-2,2′-bipyridine)](PF6)2 sensitizer, allowed us to increase the performance of the cell, reaching Jsc values of 4.0 mA cm−2, comparable to that recorded with I3−/I− (3.8 mA cm−2).