Properties Research Of Quantum Dots-light Emitting Diode Based On Graphene Electrode

Perfect graphene is an ideal two-dimensional nanomaterial of sp2-hybridized carbonatoms in a honeycomb lattice, which has excellent electronic conductivity, high opticaltransmittance, outstanding mechanical strength and good stability. As transparent conductiveelectrodes, graphene has been applied in areas ranging from solar cells, light emitting diodesto LCD panel, touch screens. ITO has been conventionally used as an anode material, but itsraw materials are becoming increasingly expensive, with high surface roughness, workfunction instability under different processing conditions, and brittleness in flexible deviceapplications. Because of these factors, researchers have to find new alternative materials,such as ZnO, PEDOT: PSS and carbon nanotubes. All the transparent conductive electrodematerials have other week points, which restrict their application. As an emerging material,graphene has received considerable attention stem from its advantages, such as low-cost,chemical stability and high optical transmittance. Colloidal quantum dots (QD) have uniqueoptical properties including good lighting stability, high photoluminescence quantum yieldand narrow emission bandwidth. There are plenty of researches on quantum dots-lightemitting diode (QD-LED) that based on ITO electrode, not graphene. This paper tries doingsome study about QD-LED based on graphene transparent conductive electrode.The chemical vapor deposition is used to prepare graphene films by comparing threetypical graphene synthesis methods. For graphene film, the transmittance is around97%across the visible spectral range, and it is monolayer under Raman spectrum, with lowdisorder and high quality. Using an AFM, it shows that graphene has a surfaceroot-mean-squares roughness of0.8nm.According to the synthesis method of Yu, CdSe core nanocrystals are firstly synthesized.Then, quantum dots of core/shell structure are synthesized using the method of SILAR. X-raydiffraction spcctra demonstrates that the preparation process has no problems. The absorptionand photoluminescence spectra of quantum dots indicate good dispersion, highphotoluminescence quantum yield of50%. The transmission electron microscopy imageshows the well-resolved regular lattice fringes, which explains good quality of quantum dots.Using OA-doped graphene film as anode, quantum dots as emissive layer, and thedevice A consists of layers in the following order, graphene/PEDPT: PSS/poly-TPD/ quantum dots/ZnO/Al. Another device B changes ITO for graphene under the sameprocessing conditions. As a result of the comparison with device based on ITO in currentdensity-voltage-luminance, current density-current efficiency-power efficiency, graphenebased QD-LED produces higher current efficiency and power efficiency, though the ITOcontrol sample exhibits higher maximum brightness and lower turn-on voltage. In a word,graphene as transparent electrode is a promising material in application.