Effects of Oxygen on the Photocarrier Dynamics in a C60 Film: Studies of Transient and Steady-State Photoconductivity

Abstract

The intrinsic dynamics of photoexcited carriers in an oxygen-free C60 film and their remarkable evolution as the film is exposed to oxygen are revealed by transient and steady-state photoconductivity (PC) measurements at various temperatures, light intensities, and photon energies. Exposure of C60 film to oxygen creates deep traps that reduce drastically the carrier lifetime and, consequently, the room-temperature steady-state photoconductivity by three to six orders of magnitude. Oxygen affects the steady-state photoconductivity excitation spectrum in a qualitatively similar way, as does decreasing the ambient temperature; in both cases, the photoconductivity decreases faster when carriers are photoexcited into the band edges. The transient and steady-state PC of a C60 film fully exposed to oxygen becomes temperature independent.