Uv Photoemission Study of 8-Hydroxyquinoline Aluminum (ALQ₃) / Metal Interfaces

Electronic structures of organic molecular materials for organic electroluminescent devices studied by ultraviolet photoemission spectroscopy

“…This value is probably more accurate than our preliminary value of 5.9 eV obtained by an electrostatic deflector-type analyzer. 12 The present value agrees with the value of 5.66 eV reported by Hamada et al 5 from the photon energy dependence of quantum yield of photoemission under atmospheric condition using an apparatus AC-1, while it is smaller than the reported value of 5.93Ϯ0.15 eV determined by an electrostatic analyzer. 9 For comparison with the observed spectrum, in Fig.…”

“…However, our recent direct UPS study of this interface by UPS measurements revealed a large shift of the vacuum level at the interface by 1.0 eV. Thus the barrier height becomes 0.3 eV, 12 which is consistent with the high electron-injecting efficiency at the Al/Alq 3 interface. This clearly demonstrates the necessity of the direct examination of the interface for deducing the real interfacial electronic structure.…”

“…The observed ionization threshold energies of these materials and their correlation with the carrier-injecting properties are also discussed. The electronic structures of interfaces including these materials have also been studied by UPS, 12,13 and will be reported elsewhere. 14…”

Energy Level Alignment and Interfacial Electronic Structures at Organic/Metal and Organic/Organic Interfaces

“…5d and 6b). We see that the injection barrier is modified from the simple expectation of Equations 1 and 2 by D. This modification is critically important for applications using carrier injection, such as EL devices [42,43] and spectral sensitization in photography.…”

“…[78] The injection gap F n B of more than 1 eV in Figure 12b between E F and the LUMO is clearly reduced in the case of Figure 12a, although the LUMO energy of Alq 3 cannot be precisely determined from only the optical bandgap of 2.9 eV. The system of Alq 3 on Au was studied by three groups, [39,70,84] and comparison of the results gives an idea of the consistency among different groups (Fig. 13), with another study by scanning tunneling microscopy (STM)related technique [95,96] to be discussed in Section 3.2.1.…”