Extrinsic electron traps in tris(8-hydroxyquinoline) aluminium

Optical time-of-flight (TOF) technique was used to measure the electron mobility of tris(8-hydroxyquinoline) aluminium (Alq(3)) exposed to different gases. When freshly prepared Alq3 sample was exposed to air, the TOF signal vas observed to be highly dispersive. After annealing the sample to 370 K for 12 h, the signal became non-dispersive. The field dependence of the electron mobility was found to exhibit Poole-Frenkel form between 250-380 K. The effects of various ambient gases (N-2, O-2, H2O) to the electron mobility were examined. It is found that O-2 acts as an extrinsic dopant and induces electron traps in bulk Alq(3).