The hole injection in hole-only devices with the structures of Al/N,N′-bis(1-naphthyle)-N,N′-diphenyl-1,1′-biphenyl-4, 4′-diamine (NPB)/ITO and Al/NPB/cobalt phthalocyanine (CoPc)/ITO were analyzed. With the combined analysis of current density-voltage and impedance measurement, the charge injection mechanism based on the injection limited current model was investigated. The NPB single layer device shows Richardson-Schottky type thermionic emission in the entire applied bias range. On the other hand, the device with the CoPc hole injection layer shows thermionic emission until the applied bias reaches 3.7 V. Increasing the bias further, Fowler-Nordheim tunneling dominates the charge injection. The changes of hole injection mechanism were discussed by evaluating the energy level changes with internal field distributions.
Bibliographical noteFunding Information:
This work was supported by a research project of the National Research Foundation of Korea ( 2013R1A1A1004778 and 2012M3A7B4049801 ) and Samsung Display Company .
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Physics and Astronomy(all)