In Situ Photoconductive Study of C60 and Phthalocyanine Thin Films

Abstract

ABSTRACTThe in situ measurement of lateral photoconductivity has been carried out on vacuum vapor deposited C60 and phthalocyanine thin films. From the photo-current increase curve during the deposition and the SEM observation of copper phthalocyanine (CuPc) thin films, it has been revealed that, at an early stage of deposition, they consist of small clusters scattered on substrate. As the thickness Increases, the clusters coalesce to eventually form continuous film. We also show that C60 thin film has considerable photoconductivity. The photo-current spectrum agrees well with the absorption one with the exception that a peak at 600 nm appears only in the former. This wavelength region corresponds to a theoretically predicted forbidden transition. An onset of photocurrent at 760 nm is assigned to the absorption edge of solid C60. The photoconductivity of C60 thin films shows a rather unusual temperature dependence In that a small drop of temperature (e.g. from 25° C to 15° C) causes a dramatic increase In photocurrent by more than two orders of magnitude.