Suppression of Charge Recombination by Vertical Arrangement of A Donor Moiety on Flat Planar Dyes for Efficient Dye-Sensitized Solar Cells.

In dye-sensitized solar cells (DSSCs), flat planar dyes (e. g., highly light-harvesting porphyrins and corroles) with multiple anchoring groups are known to adopt a horizontal orientation on TiO 2 through the multiple binding to TiO 2 . Due to the strong electronic coupling between the dye and TiO 2 , fast charge recombination between the oxidized dye and an electron in TiO 2 occurs, lowering the power conversion efficiency (η). To overcome this situation, an additional donor moiety can be placed on top of the planar dye on TiO 2 to slow down the undesirable charge recombination. Here we report the synthesis and photovoltaic properties of a triarylamine (TAA)-tethered gold(III) corrole (TAA-AuCor). The DSSC with TAA-AuCor using iodine redox shuttle exhibited the highest η-value among corrole-based DSSCs, which is much higher than that with the reference AuCor. The transient absorption spectroscopies clearly demonstrated that fast electron transfer from the TAA moiety to the corrole radical cation in TAA-AuCor competes with the undesirable charge recombination to generate long-lived charge separated state TAA⋅ + -Cor/TiO 2 ⋅ - efficiently. Consequently, the introduction of the TAA moiety enhanced the η-value remarkably, demonstrating the usefulness of our new concept to manipulate charge-separated states toward highly efficient DSSCs.