The enhanced electron injection by fluorinated tris-(8-hydroxy-quinolinato) aluminum derivatives in high efficient Si-anode OLEDs

Fabrication of organic light-emitting diodes (OLEDs) and lasers on silicon substrates is a feasible route to integrate microelectronic chips with optical devices for telecommunications. However, the efficiency of Si-anode based OLEDs is restricted by the imbalance of hole–electron injection because a p-type Si anode owns better hole injection ability than ITO. We have used fluorinated tris-(8-hydroxy-quinolinato) aluminum (FAlq3) derivatives to prepare Si-anode based OLEDs. We observed that, when tris-(5-fuloro-8-hydroxyquinolinato) aluminum (5FAlq3) is used as the electron-transporting material instead of Alq3, the cathode electron injection is enhanced due to its lower lowest unoccupied molecular orbital (LUMO) compared to the Alq3. The device can keep the relative carrier balance even when a Si anode capable of stronger hole injection was used. Further optimization of the device structure by introducing 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) as a hole blocking layer showed significant increase in the device power efficiency from 0.029 to 0.462 lm/W. This indicates that use of fluorinated Alq3 derivatives is an effective way to improve the performance of Si-anode based OLEDs.