Elucidation of the electron injection mechanism of evaporated cesium carbonate cathode interlayer for organic light-emitting diodes

Vacuum evaporated ${\mathrm{Cs}}_2\mathrm{C}{\mathrm{O}}_3$ has been proven to be an efficient electron injection material for organic light-emitting diodes. In our study, an improved quartz crystal microbalance method has been adopted to investigate the electron injection mechanism of evaporated ${\mathrm{Cs}}_2\mathrm{C}{\mathrm{O}}_3$ . It is concluded that ${\mathrm{Cs}}_2\mathrm{C}{\mathrm{O}}_3$ decomposes to metallic cesium during thermal evaporation and the thin layer of metallic cesium that is deposited onto the organic layer is responsible for the enhanced electron injection. The metallic cesium mechanism reveals that the function of the ${\mathrm{Cs}}_2\mathrm{C}{\mathrm{O}}_3$ interlayer is independent of the cathode metal, which has also been verified by our experiments.