Investigating the different conditions on solution processed MoOx thin film in long lifetime fluorescent polymer light emitting diodes

Transition metal oxides are being more frequently used as hole injection layer (HIL) in organic light emitting diodes (OLEDs), in place of polymer HILs such as PEDOT:PSS. The very thin films of the metal oxide HILs are usually deposited using vapor deposition, in order to create uniform films. Here, we report OLEDs fabricated using solution processed MoOx films as the HIL and super yellow as the emissive layer. The performance of the devices is comparable to PEDOT:PSS based devices, while the stability tests show the lifetime of MoOx-based devices is 4 x 106 h, about 40 times longer than PEDOT:PSS devices, at typical working condition. X-ray photoelectron spectroscopy (XPS) indicates both Mos(5+) and Mo6+ states in the film. The Oxygen vacant MoO3 film shows bandgap states close to valence band, as confirmed by ultraviolet photoelectron spectroscopy and optical absorption. The method show promise for all-solution processed LEDs utilizing metal oxide HILs. (C) 2017 Elsevier B.V. All rights reserved.