White-light electroluminescence from ZnO nanorods/polyfluorene by solution-based growth

Abstract

We report bright white-light electroluminescence (EL) from a diode structure consisting of a ZnO nanorod (NR) and a p-type conducting polymer of poly(fluorine) (PF) fabricated using a hydrothermal method. ZnO NRs are successfully grown on an organic layer of PF using a modified seeding layer. The EL spectrum shows a broad emission band covering the entire visible range from 400 to 800 nm. White-light emission is possible because the ZnO-defect-related emission from the ZnO NR/PF heterostructure is enhanced to become over thousand times stronger than that from the usual ZnO NR structure. This strong green-yellow emission associated with the ZnO defects, combined with the blue PF-related emission, results in the white-light emission. Enhancement of the ZnO-defect emission is caused by the presence of Zn(OH)(2) at the interface between the ZnO NRs and PF. Fourier transform infrared spectroscopy reveals that the absorption peaks at 3441, 3502, and 3574 cm(-1) corresponding to the OH group are formed at the ZnO NR/PF heterostructure, which confirms the enhancement of defect emission from the ZnO NR/PF heterostructure. The processing procedure revealed in this work is a convenient and low-cost way to fabricate ZnO-based white-light-emitting devices.

ZnO Nanorod Arrays as Electron Injection Layers for Efficient Organic Light Emitting Diodes

“…Finally, we note the differences in electroluminescence of the Device B architecture (figure 4d) compared with that reported elsewhere for ZnO NRA HyLEDs, most notably the lack of an emission peak at ~380 nm associated with ZnO band-edge emission [29,30,48] . In NRA based devices this is usually the most intense emission peak with weak contributions, attributed to emission from defect states, also reported in the 500-600 nm range.…”

“…For example Yang et al only recently first reported efficiencies for a UVemitting diode based on a ZnO NRA/poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) structure [27] -almost a decade after Könenkamp et al first reported UV emission from a diode based on the same materials [28] . Reports of visible light emission from devices of ZnO NRAs and light-emitting polymers such as polyfluorene (PFO) [29] or poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) [30] , are given by only electroluminescent (EL) emission spectra [31][32][33] .…”

Influence of the polymer concentration on the electroluminescence of ZnO nanorod/polymer hybrid light emitting diodes

“…The interaction between the ZnO NR surfaces and the PFO thin films makes the PFO link up with the ZnO, which in turn leads to ZnO NR/PFO interfaces containing strong defect emissions. 24 The PFO defect emission is attributed to the formation of on-chain defects in the presence of oxygen or fluorenone. 25 The fluorenone defects are generated through the incorporation of oxygen as O¼C bonds in the polymer backbone, which can easily be formed by electro-(or photo-) oxidation of the polymer.…”

“…26 This is ascribed to the fact that the electron mobility in ZnO NRs is higher than the hole mobility in PFO. 24 Electrons at high injection currents directly traverse at the PFO/ZnO interface and because the PFO layer is sufficiently thin (29.1 nm), the probability of an electron recombining with a hole at the PFO side becomes a minimum. This will favor an accumulation of electrons at the PFO/PEDOT:PSS interface, which may shift the recombination zone towards this interface.…”

Bicolor Light-Emitting Diode Based on Zinc Oxide Nanorod Arrays and Poly(2-methoxy,5-octoxy)-1,4-phenylenevinylene

“…14 Combining both polymers and n-type ZnO nanorods in hybrid-configuration LEDs is a novel method that makes use of the advantageous properties of both materials to provide LEDs with wide emission range. Fabrication of ZnO nanorods and polymer p-n junctions, 15 which provides an approach for the balance of the hole and electron mobility to construct high-performance LEDs, is necessary to realize practical LED applications. 16 In the current study, we designed LED based on 1D ZnO nanorods and poly(2-methoxy,5-octoxy)-1,4-phenylenevinylene (MOPPV).…”