Photoinjection of High Potential Holes into Cu₅Ta₁₁O₃₀ Nanoparticles by Porphyrin Dyes

Excited-state hole injection into the valence band of Cu₅Ta₁₁O₃₀ nanoparticles (NP-Cu₅Ta₁₁O₃₀) was investigated through sensitization with zinc porphyrin dyes using simulated solar irradiance. The Cu₅Ta₁₁O₃₀ nanoparticles were prepared by a flux-mediated synthesis and found to have an average particle size of ∼10-15 nm by DLS and TEM. The zinc 4-(10,15,20-tris(4-pyridinyl)-porphin-5-yl)phenylphosphonic acid (D1) and its analogue, in which the pyridine groups are methylated (D2), were synthesized and found to have excited-state reduction potentials appropriate for p-type dye sensitization of the nanoparticles. The dye-sensitized NP-Cu₅Ta₁₁O₃₀ exhibited fluorescence quenching consistent with electron transfer from the NP-Cu₅Ta₁₁O₃₀ to the dye; forward and recombination rates were obtained by transient absorption measurements. Hole injection times of 8 ps and <100 fs were observed for D1 and D2, respectively. Nanoparticulate films of Cu₅Ta₁₁O₃₀ were prepared and evaluated in dye-sensitized solar cells under simulated solar irradiance (AM 1.5 G, 100 mW/cm²). Measurable photocurrents and open-circuit potentials (V_oc) of 200 and 110 mV were observed using D1 and D2, respectively.