Ultrafast and long-lived photoinduced charge separation in MEH-PPV/nanoporous semiconductor thin film composites

Photoinduced charge separation and recombination dynamics were investigated in composite materials of conjugated polymer deposited on nanocrystalline metal oxide thin film. Using femtosecond IR transient absorption spectroscopy, the electron transfer from the excited state of poly[2-methoxy-5-(2-ethyl-hexyloxy)-(phenylene vinylene)] (MEH-PPV) to SnO2 and TiO2 nanoporous thin films is shown to occur with timescales of 800 and <100 fs, respectively. Negligible carrier recombination is observed for MEH-PPV/SnO2 within 1 ns. Microsecond charge recombination dynamics were measured using step-scan FTIR. Long-lived charge separation is observed in both systems, persisting for microseconds to seconds.