Comparing spiro-OMeTAD and P3HT hole conductors in efficient solid state dye-sensitized solar cells

Two hole conductor materials, spiro-OMeTAD and poly(3-hexylthiophene) (P3HT), were compared in solid-state dye-sensitized solar cells. Two org. dyes contg. one anchor unit (D35) or two anchor units (M3) were used in the comparison. Absorbed photon-to-current conversion efficiency close to unity was obtained for the devices with spiro-OMeTAD. Energy conversion efficiencies of 4.7% and 4.9% were measured for the devices with spiro-OMeTAD and the dyes D35 and M3, resp. For the devices using the P3HT hole conductor the results were rather different comparing the two dye mols., with energy conversion efficiencies of 3.2% and 0.5% for D35 and M3, resp. Photoinduced absorption measurements suggest that the regeneration of the dyes, and the polymer infiltration, is not complete using P3HT, while spiro-OMeTAD regenerates the dyes efficiently. However, the TiO2/D35/P3HT system shows rather high energy conversion efficiency and electrochem. oxidn. of the dyes on TiO2 indicates that D35 has a more efficient dye-to-dye hole conduction than M3, which thereby might explain the higher performance. The dye hole conduction may therefore be of significant importance for optimizing the energy conversion in such hybrid TiO2/dye/polymer systems.