LiF Thickness dependence of Electron Injection Models for Alq₃/LiF/Al Cathode Structure

We present the experimental evidences showing that three different electron injection models play roles in Alq₃ based organic light-emitting diodes in sequence when the thickness of LiF interlayer is changed. It is found that the device with a 0.2 nm LiF layer displays the largest current with declined luminescence. However, the one with a 0.6 nm LiF layer displays the second largest current and the highest luminescence of all. Combining with the photoluminescent test results, three models, namely chemical reaction at ternary interface, dipole effect at binary interface and tunneling enhancement effect, are expected to play roles in sequence when the LiF thickness is increased from 0 nm to 4 nm.