Chapter 27 Fabrication, physics, and chemistry toward organic nanophotonics

The complex and coupled mechanisms of charge transfer and oxidative damage in organic electronic devices have been elucidated by a new technique that combines single molecule spectroscopy with charge injection device. The experiments employed a sandwich device architecture (Au/TPD/MEH-PPV:PMMA/SiO₂/ITO), essentially a modified OLED with a charge-blocking layer (SiO₂) to suppress electroluminescence operation. The fluorescence of isolated MEH-PPV conjugated polymer molecules incorporated in the device was observed to exhibit diverse environment and electrical bias effects: (1) fluorescence quenching due to electron transfer between MEH-PPV and holes in the TPD hole-transport layer; (2) fluorescence quenching due to chemical defects at MEH-PPV generated by photooxidation; and (3) reductive "repair" of the photooxidation induced quenching by carrier injection. These results suggest a close relationship among photobleaching, charge transport, and persistent photoconductivity in organic materials. The F-V SMS is ideally suited to sort out the complex mechanism of charge transport, interface charging and actual electron transfer on a molecule by molecule, and location by location basis in a device. Furthermore, it can be applied to study other type of nanoscale materials in addition to the conjugated polymers described here.