Heavy Metal Effects on the Photovoltaic Properties of Metallocorroles in Dye-Sensitized Solar Cells

Finding strategies for effective charge separation is a prerequisite for realizing efficient solar energy conversion in photovoltaic and photocatalytic devices. Porphyrinoids, including porphyrins and related macrocycles such as phthalocyanines and corroles, are versatile ligands that can accommodate a single metal atom for most metal ions, and their photophysical and electrochemical properties can be tuned by the metal atom in the cavity. Herein, we evaluated the photovoltaic properties of the dye-sensitized solar cells (DSSCs) based on AuIII-, ReVO-, and OsVIN-corroles with COOH anchoring groups at the para- and meta-positions of the meso-phenyl groups. The DSSCs based on AuIII-corroles exhibited a power conversion efficiency (PCE) of 4.2%, which is remarkably higher than those for the ReVO- and OsVIN-corroles. Femtosecond time-resolved transient absorption measurements have shown that the electron injection from the excited singlet state competes with intersystem crossing, and that intersystem crossing for AuIII-corroles is slower than those for ReVO- and OsVIN-corroles. Consequently, the high incident photon-to-current efficiencies and resultant short-circuit current densities and PCEs for AuIII-corroles are attributed to the high electron injection efficiencies owing to the slower intersystem crossing than ReVO- and OsVIN-corroles. In addition, the higher PCE for a AuIII-corrole with a meta-COOH group (4.2%) as opposed to a para-COOH group (3.4%) is explained by the stronger Au-TiO2 interactions supported by XPS measurements and theoretical calculations. These results imply that both the substituents and the metal ion have a large influence on the photovoltaic performances. Overall, DSSCs based on the AuIII-corroles were found to exhibit the highest photovoltaic performance among corrole-based DSSCs.