Intrinsic degradation, which leads to the long-term decrease in the electroluminescence (EL) efficiency of the devices, has been a major limitation facing the new technology of organic light emitting devices (OLED). Recently we investigated degradation in OLEDs based on tris(8-hydroxyquinoline) aluminum (AlQ₃), a widely used electroluminescent small molecule. These studies showed that injection of holes in AlQ₃ is the main factor responsible for device degradation. Devices in which predominantly holes were transported through a 5 nm thick AlQ₃ layer showed a significant decrease in the photoluminescence (PL) efficiency upon prolonged current flow. In the present work we will also show that similar devices constructed in such a way to allow only electron flow through AlQ₃ did not show any decrease in PL efficiency under similar current driving conditions. This demonstrates that AlQ₃ cations are unstable and their degradation products lead to device degradation, while AlQ₃ anions are stable. Further studies of time resolved fluorescence show that the AlQ₃ degradation products are fluorescence quenchers, which cause decrease in device efficiency during prolonged operation. Comparison between fluorescence and electroluminescence decay of AlQ₃ shows that PL decay is consistently smaller than EL decay indicating that decrease of PL efficiency is not the only mechanism leading to EL degradation of AlQ₃.