| AVS 54th International Symposium | |
| Electronic Materials and Processing | Monday Sessions |
| Session EM-MoM |
| Session: | Organic Materials and Devices |
| Presenter: | C.-T. Lin, National Taiwan University |
| Authors: | C.-T. Lin, National Taiwan University G.-R. Lee, National Taiwan University C.-I. Wu, National Taiwan University T.-Y. Cho, National Taiwan University C.-C. Wu, National Taiwan University T.-W. Pi, National Synchrotron Radiation Research Center, Taiwan |
| Correspondent: | Click to Email |
Two high efficient devices will be discussed in this paper. The first is ITO/MoO3/N,N -diphenyl-N,N -bis(1-naphthyl)-1,1 -biphenyl-4,4 -diamine (NPB) based organic light emitting diodes (OLEDS). Current-voltage characteristics (I-V) and quantum-efficiency (?-J) measurements show the improvement of device performance with insertion of thin MoO3 between ITO and NPB. Ultraviolet photoemission spectra (UPS) and core-level x-ray photoemission spectra (XPS) data show that MoO3 would catch electrons from NPB and results in p-type doping in NPB. In addition, there is a significant structure transition from insulating MoO3 to metallic MoO2. As a result of high work function MoO2 in anode structure and p-type doping NPB, holes can easily be injected from ITO to NPB. The second efficient devices relate to MoO3/metal structures in tandem OLEDS. Non-stoichiometric MoO3 films consist of defect states due to O defects which pins the Fermi level in the forbidden gap. I-V characteristics show that with the MoO3 hole injection layer between anode and NPB, the current efficiency is almost identical, regardless the choice of anodes. We further investigation the interaction between low work function metals and MoO3. According to UPS and XPS results, low work function metals would easily get O atoms from MoO3, resulting in the transition to MoO2 and the increase in conductivity at the same time. The high work function of MoO3 can be tuned to relatively low work function of MoO3/Al, Mg anode. These results show that MoO3 can act as a effective hole injection layer in OLEDS, a charge generation layer in tandem OLEDS, and a high ohmic contact of metal/MoO3 in top-emitting OLEDS.