Doubly β‐Functionalized Zinc(II) Porphyrin‐sensitized TiO2 Solar Cells

Functionalized porphyrin at β‐positions with carboxylic acid groups was prepared to investigate the photovoltaic function as dye‐sensitized nanocrystalline‐TiO2 solar cells. The electronic structures of the porphyrin macrocyclic core are strongly coupled with olefinic side chains so that the absorption spectrum exhibits broad and red‐shifted Soret and Q‐bands. 2b‐Zn, which is a metallated porphyrin with 2‐propenoic acid groups at two β‐positions, exhibits the power conversion efficiency of 5.18%. From such photovoltaic performance, we can suggest that multiple pathways through olefinic side chains at two β‐positions enhance the electron injection efficiency. For improvement of the solar cell efficiency, we have employed empirical surface modification which is a post‐treatment of the TiO2 film by aqueous TiCl4. As a result, post‐TiCl4 treated cell exhibits the power conversion efficiency of 5.37% and the maximum incident photon to current efficiency of 67.2% in the Soret band region.