The electron mobilities of 4, 7-diphenyl-1, 10-phenanthroline （BPhen） doped 8-hydroxyquinolinatolithium （Liq） at various thicknesses （50-300 nm） have been estimated by using space-charge-limited current measurements. It is observed that the electron mobility of 33 wt% Liq doped BPhen approaches its true value when the thickness is more than 200 rim. The electron mobility of 33 wt% Liq doped BPhen at 300 nm is found to be -5.2 × 10^-3 cm^2/（V.s） （at 0.3 MV/cm） with weak dependence on electric field, which is about one order of magnitude higher than that of pristine BPhen （3.4 × 10^-4 cm^2/（V.s）） measured by SCLC. For the typical thickness of organic light-emitting devices, the electron mobility of doped BPhen is also investigated.
