Low-Molecular-Weight Materials: Hole Injection Materials
Low-molecular-weight hole injection materials (HIMs) are categorized as small molecules with a strong acceptor and metal oxides, and halogen derivatives. Since the relationship between the substrate work function and the ionization energy of an organic layer is important for considering the hole injection barrier, not only the HIM-dependent OLED characteristics but also the energy diagram between the anode and HIM has been extensively studied using a Kelvin probe and by ultraviolet photoelectron spectroscopy. The hole injection barrier is defined as the energy difference between the Fermi level of the anode and the highest occupied molecular orbital level of the organic layer on the anode. In this chapter, both the improvement of device characteristics using HIMs and the detailed hole injection mechanisms are summarized.
KeywordsHole injection Electron transfer Surface work function
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