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Highlights: [•] The doping effects of cesium compounds on device characteristics of OLEDs are studied. [•] The charge transport property is highly dependent on doping constituent materials. [•] The operational stability of OLEDs replies on the doping mechanism. [Copyright &y& Elsevier]

Abstract: We report on the role of cesium fluoride (CsF) doping on the enhanced electron transport properties of tris-(8-hydroxyquinolin) aluminum (Alq3) for organic light-emitting diodes. The electronic structures of CsF-doped Alq3 layers with various doping concentration are characterized by in situ ultraviolet and X-ray photoelectron spectroscopies, showing an n-type electrical doping effect with Fermi level shift towards unoccupied molecular orbital and the formation of chemistry-induced gap-states. The increase in conductivity and reduction in electron injection barrier in CsF-doped Alq3 layer with optimal doping concentration lead to the enhanced electron injection and transport, which are consistent with the improved electrical characteristics of OLEDs. [Copyright &y& Elsevier]