Charge carrier mobility in poly(p-phenylenevinylene)

Abstract

The charge carrier mobility in unsubstituted poly(p- phenylenevinylene) (PPV) is investigated by the time-of-flight (TOF) method and by the space-charge limited current transient (SCLCT) technique. Both methods are performed on devices with the configuration indium-tin-oxide/PPV/Al, which is typically used in light-emitting didoes. Hole mobilities in the range of 10 -5 cm 2 /Vs at room temperature for an electric field of about 10 5 V/cm are obtained. Field and temperature dependent TOF measurements yield an exponential increase of the mobility with the applied field and thermally activated behavior with activation energies between 0.4 and 0.7 eV on different samples. The values of the mobility at room temperature are consistent with stead-state space-charge limited currents, but considerably larger than the data from transient electroluminescence measurements. This indicates that the transit times obtained by the latter method are dominated by the much lower electron mobility rather than by the hole mobility. Assuming luminescence quenching within a distance of 20 nm to the Al contact, an electron mobility of some 10 -9 cm 2 /Vs can be estimated at room temperature and fields in the range of 10 5 V/cm.