We present the systematic study of charge carrier mobility in 4,4'-N,N'-dicarbazole-biphenyl (CBP) films doped
with a triplet-emitter material tris(2-phenylpyridine) iridium (Ir(ppy)<sub>3</sub>) - 1 wt% and 10 wt%. The hole mobility
was investigated with the time-of-flight (TOF) technique, as a function of electric field in the range 10<sup>5</sup> - 2 × 10<sup>6</sup> V/cm. For a CBP film doped with 1% of Ir(ppy)3 the hole mobility was also measured as a function of
temperature from 20° C to 70° C. The obtained hole mobilities in CBP film doped with 1% of Ir(ppy)<sub>3</sub> are in
the range 5 × 10-10 - 3 × 10-7 cm<sup>2</sup>/Vs. The measured dependence of the hole mobility on temperature and
electric field is explained in the framework of the Gaussian disorder model of Bassler. Calculated values for the
effective energetic and the positional disorder are 162 meV and 4.2, respectively. The activation energy at zero
field is 0.58 eV. The mobility extrapolated to zero field and infinite temperature amounts to 6 × 10-4 cm<sup>2</sup>/Vs.
In CBP film doped with 10% of Ir(ppy)<sub>3</sub> the hole mobilities are in the range 2 × 10-8 - 3 × 10-7 cm<sup>2</sup>/Vs. The observed increase of the hole mobility in Ir(ppy)<sub>3</sub>-doped CBP films with increasing doping concentration can be
attributed to hopping transport of charge carries via dopant molecules.