Hole injection and transport in tris-(8-hydroxyquinolinato) aluminum

Time-resolved measurements of the passage of holes through thin layers of tris-(8-hydroxyquinolinato) aluminum (Alq) sandwiched between two hole-transporting layers give an effective mobility of order ${10}^{\text{−6}}{\text{–10}}^{\text{−5}}\hspace{0.17em}{\mathrm{cm}}^2/\mathrm{V\hspace{0.17em}s},$ hole range of 10–30 Å, and effective activation energy of 0.12 eV. Phenomenological mobilities, hole ranges, and overall transmission probabilities through the Alq depend strongly on electric field strength and temperature. These hole injection and transport characteristics of Alq affect the behavior of electroluminescent devices based on these materials and, in particular, the location of the recombination zone.