Inverted polymer LEDs with solution-processed nano-hybrid electron buffer layers

Abstract

We fabricated multilayered inverted polymer-based LEDs (iPLEDs) consisting of several types of solution-processed electron injection layer (EIL)/F8BT [green light emitting polymer (LEP)] or polyfluorene-based blue LEP (PFO)/TFB (hole-transporting layer)/MoO3/Ag structures. We compared the electrical properties of hybrid iPLEDs with solution-processed hybrid EILs deposited at low temperature (<120 °C) consisting of ZnO/polyethyleneimine (PEI), PEI/tantalum oxide nanosheet (TaO-NS), and PEI/TaO-NS/TmPyPB multilayers. The combination of PEI dipole and ultra-thin TaO-NS (∼1 nm) layers improved the EL efficiency and operating voltages owing to the energy level shift of ∼1 eV and the effective hole blocking at the ITO/TaO-NS/LEP interface. However, a considerable barrier height of >0.5 eV still existed at the TaO-NS/PFO interface. The insertion of electron-transporting small molecules between the TaO-NS and PFO layer effectively reduced the electron injection barrier height and electron transport properties of the multilayered iPLEDs resulting in improved EQE and operating voltage for the blue-light iPLEDs.