Electron-only devices with different structures were prepared by doping Liq (8-hydroxyquinolinato-lithium) into the electron transport layer Alq (tris(8-hydroxyquinolinato)aluminum). The experimental results show that the electrical properties of doped devices are inferior to those of non-doped devices with Liq/Al composite cathodes and superior to those of non-doped devices with Al only cathodes, implying that Liq’s doping in Alq exhibits dual roles without causing a significant “n-doping” effect: Liq molecules dispersed in Alq near Alq/Al cathode interfaces display as electron injection layers, which enhances the device currents by enhancing electron injection; those in the bulk of Alq after doping have a detrimental effect on electron transport due to their own poor conductivity, consequently decrease the device currents. In the tests of electroluminescent devices, the doping of Liq shows a similar behavior, the performance of Liq-doped device is between the non-doped devices with Liq/Al cathode and Al cathode structures, with maximum current efficiencies of 3.96, 4.27 and 2.27 cd/A for the three devices, respectively, and no charge transfer is observed in the absorption and photoluminescence spectras.