Fabrication And Properties Of CdSe/ZnS Quantum Dots-based Flexible Quantum-dot Light-emitting Devices

Quantum-dot Light-emitting Devices(QLEDs)have attracted much attention due to their unique advantages such as narrow emission linewidth,tunable color emission spectral window across the visible to near-infrared range,cost-effective fabrication techniques compatible with solution processed methods,and so on.And QLEDs can avoid the disadvantages of Organic Light Emitting Device(OLED)which have wide full width at half maximum,poor luminescence stability and complicated preparation process.Meanwhile,QD is an inorganic material,so the encapsulation of QLEDs is more simple.Therefore,the flexible QLEDs are highly promising for the next generation of lighting and displays.However,the preparation of QLEDs can be further optimized.In addition,there are very few studies on the white QLEDs with flexible substrates.So the investigations of this article are as follows:Firstly,the effect of different preparation parameters for poly-TPD films and CdSe/ZnS QDs films was studied.Then the orange QLEDs based on glass substates were fabricated.The results indicate that the device has a better performance when the concentration of poly-TPD is 2 mg/mL,the annealing temperature is 110 ? and the layer of QDs with a concentration of 7.5 mg/mL is spin-coated at 2000 rpm,dried at 80 ?.The device can produce orange light and the CIE color space for the QLEDs is(0.61,0.35).The device emits pure orange light with a narrow FWHM bandwidth of 30 nm and high brightness up to 1607 cd/m2.The QLED has a low EL turn-on voltage of about 3 V.The maximal current efficiency of the device is 1.71 cd/A.Subsequently,the orange QLEDs based on flexible ITO substrate were fabricated.The PEDOT:PSS layer was spin-coated on the flexible substrate to increase its conductivity after plasma treatment.2%ratio of dimethyl sulfoxide(DMSO)were added into the PEDOT:PSS solvent to enhance its conductivity.The results indicate that the device has a better performance with the device structure based on hybrid layer of HTL:QDs.The argon(Ar)plasma treatment was utilized to improve the performance of QLEDs.It is indicated that the device can produce the best performance after plasma treatment for 20 s at Ar gas flow rate of 26 sccm.The maximal current efficiency of the flexible device is 1.38 cd/A.Finally,a flexible white QLEDs was constructed.The device structure of the white device was PET/ITO/PEDOT:PSS/poly-TPD/DPVBi:QDs/Bphen/DPVBi/Bphen/Alq3/LiF/Al.And when the ratio of QDs:DPVBi is 1:2,the color coordinates is(0.35,0.31)which is close to the standard white point.The PVK was added in the emitting layer to adjust quantum dots distribution in polymer matrix.The flexible white QLEDs exhibited an efficiency of 1.04 cd/A at a CIE 1931 chromaticity of(0.33,0.30)when the concentration of PVK was 20 mg/ml.In conclusion,high quality orange and white flexible QLEDs were fabricated successfully.This study suggested that flexible QLEDs may find potential applications in displays and lighting.