Thienopyrroledione-Based Photosensitizers as Strong Photoinduced Oxidants: Oxidation of Fe(bpy)₃²⁺ in a >1.3 V Dye-Sensitized Solar Cell

The design of visible light absorbing organic dyes as strong photoinduced oxidants is needed for many potential applications in energy production and storage. To access more positive potentials, the electron deficient thienopyrroledione building block is promising as a π-bridge combined with weak aryl-ether donor groups and the phenyl-cyanoacetic acid acceptor group. The thienopyrroledione (TPD) building block is compared to the ubiquitous benzothiadiazole (BTD) building block, which was recently used in a dye-sensitized solar cell (DSC) device with >1.4 V photovoltage output. The variation in dye donor group is studied through UV–vis absorption spectroscopy and electrochemical methods both in solution and on TiO2 films. The TPD building block resulted in a more positive ground state and excited state oxidation potential, a higher photocurrent (up to 3.5 mA/cm2), and a higher power conversion efficiency (up to 2.9%) than a BTD analogue while retaining comparable photovoltages (∼1.3 versus ∼1.4 V). Computational analysis was used to better understand the optical properties of the thienopyrroledione-based dyes showing overlap of orbitals at the TPD bridge in the S0 and S1 states. The dyes were analyzed in high voltage-DSC devices with a challenging to oxidize redox shuttle, Fe(bpy)32+, at 1.37 V versus NHE.