IN-SITU PHOTOCONDUCTIVITY BEHAVIOR OF C-60 THIN-FILMS - WAVELENGTH, TEMPERATURE, OXYGEN EFFECT

Uv-visible absorption, luminescence (excitation, emission), photoconductivity and conductivity measurements have been performed on polycrystalline C60 thin films, in situ or exposed to oxygen. The shape of the emission spectrum is irrespective of the excitation energy, indicating that internal conversion takes place to the lowest localized electronic state. Sigma(d) and sigma(ph) in the high temperature regime (T>270K) are thermally activated Ea(sigma(d))=0.50+/-0.05 and Ea(sigma(ph))=0.20+/-0.05eV whereas at low temperature regime (T<270K) they are almost temperature independent, for all excitation wavelength above the photoconductivity edge (Eg(el) almost-equal-to 1.7eV or lambda almost-equal-to 730nm). Carrier photogeneration and transport processes are invoked in the context of localized electronic states. Oxygen effects on sigma(d) and sigma(ph) are interpreted.