Zinc oxide nanorods/polymer hybrid heterojunctions for white light emitting diodes

Abstract

Abstract Zinc oxide (ZnO) with its deep level defect emission covering the whole visible spectrum holds promise for the development of intrinsic white lighting sources with no need of using phosphors for light conversion. ZnO nanorods grown on flexible plastic as substrate using a low temperature approach (down to 50 o C) were combined with different organic semiconductors to form hybrid junction. White electroluminescence (EL) was observed from these hybrid junctions. The configuration used for the hybrid white light emitting diodes (LEDs) consists of two-layers of polymers on the flexible plastic with ZnO nanorods (NRs) on the top. The inorganic/organic hybrid heterojunction has been fabricated by spin coating the p-type polymer Poly (3, 4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) for hole injection with an ionization potential of 5.1 eV and Poly(9, 9-dioctylfluorene) (PFO) is used as blue emitting material with a bandgap of 3.3 eV. ZnO nanorods (NRs) are grown on top of the organic layers. Two other configurations were also fabricated ; these are using a single MEH PPV (red emitting polymer) instead of the PFO and the third configuration was obtained from a blend of the PFO and the MEH PPV. The white LEDs were characterized by scanning electron microscope (SEM), x-ray diffraction (XRD), currentvoltage (I–V) characteristics, room temperature photoluminescence (PL) and electroluminescence (EL). The EL spectrum reveals a broad emission band covering the range from 420 to 800 nm, and the emissions causing this white luminescence were identified.