Voltage-Enhancement Mechanisms of an Organic Dye in High Open-Circuit Voltage Solid-State Dye-Sensitized Solar Cells

Sensitization of solid-state dye-sensitized solar cells (SSDSSCs) with a new, organic donor-π-acceptor dye with a large molar absorption coefficient led to an open-circuit voltage of over 1 V at AM1.5 solar irradiance (100 mW/cm2). Recombination of electrons in the TiO2 film with the oxidized species in the hole-transfer material (HTM) was significantly slower with the organic dye than with a standard ruthenium complex dye. Density functional theory indicated that steric shielding of the electrons in the TiO2 by the organic dye was important in reducing recombination. Preventing the loss of photoelectrons resulted in a significant voltage gain. There was no evidence that the organic dye contributed to the high voltage by shifting the band edges to more negative electrode potentials. Compared with an iodide-based liquid electrolyte, however, the more positive redox potential of the solid-state HTM used in the SSDSSCs favored higher voltages.