Self-assembled multinuclear complexes for cobalt(II/III) mediated sensitized solar cells

In this work, we designed a tetranuclear self-assembled dye 4 (2Z907-Ag+-(Ru(TMAM))) exploiting a combination of the antenna effect and positively-charged groups designed to repel the oxidized form of cationic cobalt redox mediators, in order to reduce recombination and increase the efficiency of dye sensitized solar cells (DSSCs). Charge transfer and excited dynamics were probed by photoelectrochemical and photophysical measurements. The sensitized cell performance, recorded with a [Co(bpy)3]3+/2+ redox mediator and PEDOT counter electrode, showed an improvement when passing from Z907 to the multinuclear systems. The enhancement of the efficiency compared to Z907 resulted mainly from a superior steric and electrostatic shielding determined by the simultaneous presence of long alkyl chains and quaternary ammonia ion units in the architecture of 4.