Effect of polar dopant on energetic and positional disorders in tris(8-hydroxyquinolinato) aluminum (Alq3)

The influence of polar dopant on the charge carrier transport in amorphous tris (8-hydroxyquinolinato) aluminum (Alq(3)) was studied by time-of-flight measurement. The 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) was doped into Alq3 with various concentration from 0.5 to 24 wt.%. The electron mobility was reduced by about one order by DCM doping in Alq3. The electric-field dependence electron mobility in Alq3: DCM films separated into two discrete regions of critical fields root E-c. The value of root E(c)ranged from 360 to 405 (V/cm)(1/2) depending on the DCM concentration in Alq3 films. The energetic disorder in Alq3: DCM films increased from 0.01 eV to 0.09 eV with DCM doping concentration. The positional disorder in Alq(3):DCM films also increased from 0.3 to 6.5 with DCM doping concentration up to 24 wt.%. These results indicated the strong Coulombic and dipole-dipole interactions between DCM and Alq(3) molecules. The interactions between randomly located DCM molecules, Alq(3) dipoles and oriented dipoles are the major caused of positional disorder.