The Research Of Novel Quantum Dot Electroluminescent Devices And Carrier Transport Regulation

Quantum dots?QDs?has attracted tremendous interest owing to their outstanding properties of low cost,high color saturation,tunable band gap,good photo-and thermal-stability,etc.,showing great application value in electroluminescent devices.As novel quantum dot electroluminescent devices,the light-emitting diodes based on perovskite quantum dots and the light-emitting field-effect transistors?LEFETs?based on quantum dots have many advantages over the traditional quantum dot light-emitting diodes?QLEDs?,and have good application prospects in the field of solid state lighting and flat panel display.This dissertation aims to regulate the carrier transport of novel quantum dot electroluminescent devices.By changing doping concentration of the electron transport layer and inserting the insulation layers,we can improve the carrier injection and transport balance of perovskite light-emitting diodes?Pe LEDs?and quantum dot light-emitting field-effect transistors?QLETs?,respectively,thus improving the performance of novel quantum dot electroluminescent devices.The main contents are as follows:?1?The nickel oxide?NiO_x?film prepared by solution method is adopted as hole injection layer of the formamidinium lead halide perovskite?FAPb Br₃?Pe LEDs to substitute detrimental PEDOT:PSS.Compared to the control device with PEDOT:PSS hole injection layer,the resulting device based on NiO_x film shows more than twofold operating lifetime enhancement.For further enhancing the performance of FAPb Br₃QLEDs,two metal dopants?Cs and Li?are introduced to improve the hole injection capability of NiO_x film and the charge carriers balance of device.With Hall measurements,both NiO_x and Cs/Li-doped NiO_x demonstrate a fully p-type semiconductor characteristic.Increased concentration of doping in the film would result in an increase in carrier concentration and a decrease in carrier mobility.This decreased carrier mobility results from the increased scattering due to grain boundaries and impurity phases,seriously at high Cs/Li concentrations.As a result,the device,based on the NiO_x film?doping 2 mol%Cs?,shows the best performance with maximum brightness of 2970 cd/m² and external quantum efficiency?EQE?of 11.0%,which is nearly 2-fold enhancement in efficiency compared to the PEDOT:PSS-based device.The results pave the way for highly efficient and stability perovskite QLEDs based on FAPb Br₃ QDs.?2?The high performance Hf doped Zn O?Hf-Zn O?flexible thin film transistors?TFTs?were fabricated using Ag nanowires?NWs?as gate electrode and high-k Hf O₂as dielectric.The field effect mobility of Hf-Zn O is 14.7 cm²/?V·s?,on/off ratio is more than 10⁶,and the subthreshold swing is about 0.26 V/dec.Furthermore,after 5000bending cycles test,the TFTs with Ag NWs still maintain a superior performance,such as the high mobility of 12.6 cm²/?V·s?and the small subthreshold swing of 0.33 V/dec.The operating voltage of Hf-Zn O is only 5 V,showing the great potential of application in low-powered devices.We also fabricated the resistor-loaded inverter based on the flexible TFTs.The shift of input voltage is negligible with different supplied voltages,indicating the highly-stable property of the inverter.As a result,the low consumption optoelectronics provide great inspiration for researchers to construct the next generation high performance wearable and flexible devices.?3?The interface between QDs emitting layer?EML?and hole transport layer?HTL?is modified by the use of polyethylenimine ethoxylated?PEIE?,which acts as a buffer layer to optimize the bandgap alignment between HTL and EML,and passivate the QDs.In addition,the modification of the interface between EML and electron transport layer?ETL?by using methylammonium bromine?MABr?for better carrier transport balance.The interface engineering in the device results a peak EQE of 21.0%and a high brightness of 12240 cd/m².These findings regarding the carrier transport in the multilayered devices suggest that energy level management and interface modification is extremely important for the performance of electronic devices.