Application Of Nickel Oxide As Hole Injection Layer In Green QLEDs Device

In both academia and industry,quantum light-emitting diodes(QLEDs)have been recognized as an emerging display technology due to their competitive device performance.Because it can change their electroluminescence peak by adjusting the size of the quantum dots(QDs),QLEDs have a lower production cost,wider color gamut,and high color purity,compared to organic light-emitting diodes(OLEDs).So it has a good application prospect as the next generation solid state lighting source.But the conventional QLEDs device uses organic PEDOT:PSS as the hole transport layer,when QLEDs device was exposed in air,it will absorb water and oxygen so as to decrease their lifetime.However,as a metal oxide,nickel oxide(NiO)has a deep energy level,a high stability in air,high transmittance and hole mobility.Therefore,we chose NiO as the hole injection layer(HIL)and CdSe@ZnS quantum dots as the luminescent layer to construct the green QLEDs devices.This paper will introduces our work from three aspects.(1)Fabrication and investigation of green CdSe@ZnS QDsThe advantages and disadvantages of fluorescent QDs directly affected the performance of QLEDs devices.So we used the hot injection method and synthetized CdSe@ZnS QDs.Then we characterized the CdSe@ZnS QDs by transmission electron microscope,which showed that CdSe@ZnS QDs have good dispersity,uniform size.At the same time,CdSe@ZnS QDs were characterized by fluorescence,we obtained CdSe@ZnS QDs with a fluorescence wave of 516 nm and 83.58%of quantum yield.With the increase of nucleation time,fluorescence peak have a 15 nm red shift.Subsequently,CdSe@ZnS QDs were characterized by ultraviolet electron spectrum(UPS)and discovered that the valence band of CdSe@ZnS QDs is about 5.47 eV.So when CdSe@ZnS QDs are used as the luminescent layer of QLEDs can effectively improve devices performances.(2)Fabrication and investigation of NiO nanocrystallineWe prepared high quality NiO nanocrystal by solution method and found NiO can decrease their size by add lithium stearate(Li St).When LiSt is adjusted from 0 mmol to 0.4 mmol,the size of NiO can change from 5.7 nm to 2.4 nm.Then we characterized NiO by X-ray diffraction(XRD),we obtained NiO with five diffraction peaks.XPS results show that the O1s spectra and Ni 2p3/2 spectra are more or less deviated from the NiO standard spectra.At the same time,we have carried on the ultraviolet electron spectrum(UPS)of the NiO and discovered that the valence band of NiO is about 5.85 eV.Subsequently,the transmittance and hole mobility of NiO films was measured and reached 91.17%and 30.56 cm~2/Vs.These results indicate that NiO are suitable as hole injection materials.(3)NiO nanocrystalline were used as hole injection layers and Cd Se@ZnS QDs were used as luminescent layers to assembling green QLEDs devicesWe firstly constructed the QLEDs device with Cd Se@ZnS green QDs.Compared with red and blue QLEDs devices,Green QDs has a smaller red shift between electroluminescence spectra(EL)and the photoluminescence(PL)spectrum.At the same time,green QLEDs devices obtained the maximum luminance of 54760 cd/m~2.Subsequently,we put NiO film as the HIL by adjusting various parameters,we finally obtained a green QLEDs device with a maximum luminance value of 59188 cd/m~2 and lifetime of58356 s.Their brightness is 10%higher than that of PEDOT:PSS-based devices and lifetime is almost9-folds compared with PEDOT:PSS-based devices in air.We believe that Ni O of HIL can improve the stability of the QLEDs in air,which is more promising to the mass production of QLEDs in commercial applications.