Investigation Of Charge Injection Characteristics And Luminescence In Inverted Organic Light-emitting Diodes

Organic light-emitting diodes (OLEDs) have attracted broad attention due to their great promise to be the solid-state lighting and full-color displays of the future. Compared with the conventional OLEDs, inverted OLEDs should be more preferable for the active-matrix OLEDs (AM-OLEDs) displays based on the n-channel TFT backplane. In this thesis, we have investigated charge injection characteristics and luminescence of inverted OLEDs. The details are as follows:1. A series inverted OLEDs were successfully fabricated using Al/DPSF (2,7-bis(diphenylphosphoryl)-9,9’-spirobi[fluorene]) as the electron-injection layer. It is found that the electron injection barrier between ITO and the light-emitting layer can be significantly reduced at present of Al/DPSF. The performance of the inverted OLEDs can be comparable with the conventional OLEDs.2. Inverted OLEDs fabricated by thermal evaporation using Li2CO3(Cs2CO3) doped polyethylenimine(PEI) as the electron-injection layer exhibited a maximum current efficiency of45.7cd A-1and40cd A-1at the luminance of1000cd m-2,indicates Li2CO3(Cs2CO3) doped PEI is a good electron injection layer for inverted OLEDs.3. Based on solution-processed, we fabricated blue, green, red and white inverted OLEDs by using Li2CO3doped PEI as the electron-injection layer. A high external quantum efficiency (EQE) of15.2%at the luminance of158cd m-2was obtained in the blue inverted OLEDs. The maximum current efficiency of34.3cd A-1was achieved, and rolls off slightly to30.8cd A-1at the luminance of1000cd m-2.The white inverted OLEDs with CIE (0.360.44) and showed a maximum current efficiency of38.0cd A-1.Further study indicating that reaction between ITO and PEI, which would lower the injection barrier between ITO and the organic layer.