Dynamics of photoexcited charge carriers in pristine C/sub 60/ films: study of the time-resolved transient photoconductivity

Summary form only given. The intrinsic dynamics of photoexcited charge carriers in pristine C/sub 60/ films are investigated by the time-resolved transient photoconductivity (TPC) measurements. The transient photocurrent exhibits an initial short-lived component followed by a long-lived tail. The short- and long-lived components vary differently with temperature, light intensity, and photon energy. The fast short-lived component shows a linear or slightly superlinear intensity dependence, depending on the photon energy, whereas the long-lived component shows a sublinear dependence. The non-exponential, intensity-dependent decay rate of the TPC implies that non-geminate carrier recombination prevails. The peak TPC shows a maximum at about T/spl tilde/240 K, near the structural phase transition temperature, and becomes temperature independent below about 60 K. In contrast, the long-lived component exhibits a thermally activated behavior with an activation energy of about 18 meV, indicating that thermalized charge carriers undergo multiple trapping in shallow traps. Exposure of the pristine C/sub 60/ films to air creates deep traps which significantly decrease the carrier lifetime and quenches the long-lived tail.