Regulation of dithiafulvene-based molecular shape and aggregation on TiO2 for high efficiency dye-sensitized solar cells

A well-matched relationship between the molecular shape and aggregation of donor--acceptor (D--A) organic dyes is of great significance for realizing the principle of maximizing the performance of dye-sensitized solar cells (DSCs). To this end, two dithiafulvene-based organic sensitizers with different molecular shapes were synthesized, and the influence of their aggregation on TiO2 on the various performance parameters of DSCs was investigated. It was found that V-shaped DTF-C5, with a larger flare angle of 150.6 degrees between the donor and acceptor units in the molecular structure, tended to form compact aggregates on the surface of TiO2 without the loss of adsorbed dyes, thus giving a higher short-circuit density (J(sc)) of 14.92 mA cm(-2) and a power conversion efficiency (PCE) of 7.39%; these values were 1.48 and 1.53 times higher than those of a DSC with a CDCA co-adsorbent, respectively. On the other hand, DTF-C6, possessing a typical V-shaped conformation with a flare angle of 120.6 degrees, needed to co-adsorb with CDCA to fill the vacant sites between the dye aggregates on the TiO2 surface, with the aim of reducing current loss and suppressing electron recombination. Compared to a DSC with pristine DTF-C6 aggregation, an example based on the co-adsorbed system dramatically raised the PCE from 5.50% to 9.04%, owing to the improved J(sc) and open-circuit voltage values. This work presents a perspective for the rational regulation of molecular shapes and the dye aggregation of organic dyes for highly efficient DSCs.