Molecular dipole, dye structure and electron lifetime relationship in efficient dye sensitized solar cells based on donor-π-acceptor organic sensitizers

In this work we report the synthesis and characterization of two new push–pull organic dyes (LC95 and LC107) to be employed as sensitizers in solar cells. Both molecules contain the bis(4-hexyloxyphenylamino)styril unit as the donor group, the cyanoacrylate acid as the acceptor, and the selenophene–thiophene (LC95 dye) and thiophene–selenophene (LC107 dye) moieties as the conjugated linkers. Dye sensitized solar cells employing these two photosensitizers and the cobalt(II/III) redox electrolyte exhibit good solar to energy conversion efficiencies of 6.3% and 6.5% measured under the 100 mW cm⁻² simulated AM1.5 sunlight. The efficiencies are slightly lower with the iodine/iodide electrolyte. The performance of these two dyes has been discussed and compared to three closely related sensitizers, i.e. C214, C216 and C218, by means of experimental measurements and quantum chemistry computations, with special attention to differences on their geometries, molecular dipoles and electron recombination lifetimes.