Double D–π–A branched dyes – a new class of metal-free organic dyes for efficient dye-sensitized solar cells

Abstract

Double branched donor acceptor compounds (D–π–A)₂L, whose separate branches are linked by saturated chains or ring systems, are highly promising sensitizers for dye-sensitized solar cells (DSSCs). Their photovoltaic performance η (power conversion efficiency PCE) is higher than the η value of the corresponding single branched sensitizers D–π–A. This advantage can be attributed to the lower aggregation tendency and to the higher loading density of the chromophores on the semi-conductor surface (TiO₂). Moreover, the intramolecular transfer of the excitation energy can enhance the contact time of the adsorbed dye molecules in the excited state S₁ and thus reduce the unwanted charge recombination (dark current).