A comparative study on the performances of organic light-emitting diodes with C60 and C70 cathode buffer layer

Organic light-emitting diodes based on Alq(3) (8-hydroxyquinoline aluminum) were fabricated using C-60 and C-70 as cathode buffer layer, respectively. The results showed that EL performances of OLEDs using C-70- buffer-layer were better than that of C-60- buffer-layer. The mechanisms of enhancement were systemically discussed on the energy level difference of the heterojunction, conductivity of the materials and electron transport and quantum current distribution in the two kinds of fullerene molecules. The degradation of the two kinds of OLEDs exposed in air without encapsulation was also studied. It was found that OLEDs using C-70 as cathode buffer layer showed a better stability. This is because C-60 can be easily destroyed by oxygen than C-70. Thus, C-70 cathode buffer layer can not only increase the EL characteristics, but also dramatically improve the stability of OLEDs.