Influences Of Different Function Layers On The Performance Of Quantum Dots Light-emitting Diodes

Quantum dots is excellent performance fluorescent material because of its wide range of excitation spectrum, narrow photoluminescence spectra, emitting light colors can be adjusted by the size of nanoparticle, good photochemical stability, high electron mobility, Quantum dots have great application potential in electroluminescent devices. QLED have been extensively studiedand developed for the next generation displays and solid-state lighting due to the facile solution processable materials, advantageous pure and saturated colors, tunable emissions, and feasibility of large scale synthesis of colloidal quantum dots. Such characteristics are much superior to the organic light emitting diodes (OLED).In this thesis, the enhancement of the electroluminescent performance of QLED by improving the injection and transporting of carrier is researched. (1) Poly-TPD and PVK are used as hole transport material, mixed solution spin coating and layer by layer spin coating are prepared for hole transport layer in the devices. Both the devices exhibit the superior performance in current and luminescence characteristics in comparison with normal device. In mixed hole transport layer devices, the blend ratio of Poly-TPD:PVK influence the device performance. When the blend ratio is 1:1, the device obtain optimum performance. In layer by layer hole transport layer devices, the PVK film thickness decides the carrier injection, when the PVK concentration is 4mg/mL, the luminance of the device is maximum. (2)In the inverted green quantum-dot light emitting diode, ZnO-NPs is used as electron transport material.PFN, which has excellent electron transport ability, is inserted as buffer layer between the hole transport layer and emitting layer in order to enhance the electron injection and transporting. When the PFN spin coating speed is 2500rpm, the device showed superior device performance,in particular significantly improved luminance. In the end, The composite components with a system in which core shell structure blue-emitting quantum dots(CdSe/ZnS) doped in the polymer of poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV)serves as the active layer have been fabricated. With a systematical investigation, we report the electroluminescent spectrum and the effect of different QDs doping concentration (mass fraction) in device luminescence performance. Besides, the non-doped devices are also fabricated. By comparing the analysis, the strength of carrier transporting in doped and non-doped devices are investigated.Studying enhance the injection and transporting of carrier in QLED can balance the positive and negative carrier,decrease leakage current, improve luminescence performance in the devices.lt provides important guidance for commercialization of QLED.