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

Abstract

The influence of polar dopant on the charge carrier transport in amorphous tris (8-hydroxyquinolinato) aluminum (Alq3) 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 Ec1/2. The value of Ec1/2ranged 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 Alq3: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 Alq3 molecules. The interactions between randomly located DCM molecules, Alq3 dipoles and oriented dipoles are the major caused of positional disorder.