Qiaoli Niu

Ultrathin nickel oxide film as a hole buffer layer to enhance the optoelectronic performance of a polymer light-emitting diode

In order to promote a polymer LED (PLED), we fabricated and introduced an ultrathin nickel oxide (NiO) buffer layer (<10 nm) between the indium tin oxide (ITO) anode and the poly (3, 4-ethylenedioxythiophene) hole injection layer in the PLED. The NiO buffer layer was easily formed on the ITO anode by electron-beam deposition of a nickel (Ni) metal source and an oxygen plasma treatment process. As a result, the PLED device with the NiO buffer layer on its ITO anode had the same turn-on voltage as conventional PLED devices without the NiO buffer layer, and the luminance of the PLED device with the NiO buffer layer was doubled, compared with the conventional PLED devices without the NiO buffer layer. Improvement of the optoelectronic performance of the PLED can be attributed to the increase of the current driven into the diode, resulting from the NiO buffer layer, which can enhance the hole injection and balance the injection of the two types of carriers (holes and electrons). Thus it is an excellent choice to introduce the NiO buffer layer onto the ITO anode of the PLED devices in order to enhance the optoelectronic performance of PLED devices.

Enhancing the performance of organic-inorganic hybrid light-emitting diodes by inserting a conjugated polyelectrolyte interlayer

Hybrid light-emitting diodes (HyLEDs) incorporating the advantages of organic and inorganic semiconductors, were promising to realise efficient electroluminescence with air-stable charge-injection interfaces. However, HyLEDs with only inorganic semiconductor such as zinc oxide (ZnO) as electron-injection layer suffered from low devices efficiencies due to large electron injection barrier. To improve the electron injection, conjugated polyelectrolyte poly[(9,9-bis(3’-(N,N-dimethylamino)propyl)-2,7-fluorene) -alt-2,7-(9,9-dioctylfluorene)] (PFN) was used together with ZnO as electron-injection layer by fabricating it on top of ZnO. Experimental data showed that the light efficiencies of HyLEDs were almost doubled after the insertion of PFN. The performances enhancement was attributed to the reduced energy barrier for electron injection from ZnO. The electron current increased. And therefore, the balance of electron and hole currents was improved.

High efficiency double-layer white polymer light-emitting diode

In this presentation, efficient white polymer-light-emitting diodes have been fabricated with double emissive layers. The device structure consists of ITO/poly(ehtlenedioxythiophene): poly(styrene sulfonic acid) (PEDOT: PSS) / poly(N-vinylcarbazole) (PVK) /phenyl-substituted PPV derivative (P-PPV)/poly(9,9-dioctylfluorene) (PFO)/Ba/Al. By tuning the thickness of the emissive layers, white light was obtained. In EL spectra of the white light, the full width at half maximum (FWHM ) of the green band from P-PPV increased from 79 nm to 110 nm. Therefore, the EL spectra can cover the whole visible area. The 1931 CIE coordinates of the white light emission obtained were (0.31, 0.36). The maximum luminous efficiency is 3.8cd/A.