Photocurrent Spectra and Fast Kinetic Studies of P3HT/PCBM Mixed with a Dye for Photoconversion in the Near-IR Region

Photoconversion properties are demonstrated for a device based on a small dye molecule, absorbing light in the near-IR region, mixed with two organic charge transport materials and together forming a dye-sensitized organic bulk heterojunction. The organic dye molecule, phthalocyanine (1,4,8,11,15,18,22,25-octabutoxy-29H,31H-phthalocyanine), mixed with a blend of poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C-61 (PCBM), shows a photoconversion spectrum extended more than 150 nm toward longer wavelengths, as compared to a device without such dye sensitization. In the dye-sensitized region of the photoconversion spectrum the maximum infernal quantum efficiency was estimated to 40%. With higher dye concentrations the internal quantum efficiency decreases. Transient laser spectroscopy measurements show that after excitation of the dye there is an electron transfer from the dye to PCBM and a subsequent hole transfer from the dye to P3HT, which results in a long-lived (P3HT(+)/dye/PCBM-) charge-separated state.