Study On The Modification Of Carrier Injection To Improve The Performance Of Organic Electroluminescent Devices

Organic light-emitting devices（OLEDs）have been the intensive investigation subject in recent years due to their applications in lighting and displays.The typical OLED structure usually consists of a transparent indium-tin-oxide bottom anode,a top metal cathode,and some organic layers sandwiched between electrodes.After 30years of unremitting efforts,the performance of OLEDs has been close to the level of inorganic semiconductor light-emitting devices.However,in order to achieve the final application goal of dynamic panchromatic HD display,the luminous efficiency and stability of the device need to be further improved.Especially because organic materials are not resistant to high temperature,improving the luminous efficiency of the device and reducing the heat loss become the key to improving the stability and service life of the device.One of the important reasons that affect the luminous efficiency of OLEDs is the carrier imbalance injection.Therefore,in this thesis,the following three tasks have been done from the carrier injection capability to improve the device performance:PEDOT:PSS was spin-coated on the functional layer of the device by spin coating,and the structure was successfully prepared as ITO/PEDOT:PSS（15nm）/PFO（80nm）/PEDOT:PSS（40nm）/PFO（80nm）/Al（70nm）stacked organic electroluminescent device.By studying the current-voltage（I-V）characteristics,voltage-luminance（V-L）characteristics,and current-efficiency（I-E）characteristics of the stacked device,it is found that the stack has not been optimized in anyway.The device has a lighting voltage of 12.3 V and a lighting current of 1.39u A.The current efficiency（3.97 cd/A）is 8 times the current efficiency of the single-layer comparison device.More importantly,this new PEDOT:PSS new multilayer device connection layer requires neither high temperature evaporation coating nor doping.Molybdenum oxide（MoO₃）,which is inexpensive,was used as the hole injection layer of the device,and a structure of ITO/MoO₃（y nm）/NPB（60nm）/Alq₃（80nm）/CsCl（0.5nm）/Al（120nm）was prepared by a vacuum thermal evaporation method)organic electroluminescent device.By comparing（y=1,3,5,7nm）the performance of devices fabricated with four thicknesses of MoO₃thin film,analyzing the device's J-V and L-V data,it is found that when the thickness of the MoO₃thin film is 5nm,the device lighting voltage is only 2.5V;When the device voltage is 9.25V,the maximum brightness is 43580cd/m².When the current density is647.92m A/cm²,the maximum current efficiency of the device is 6.73cd/A.The device's brightness and lighting voltage performance are optimized at the same time.Compared with ordinary standard devices,the luminous brightness and current efficiency are increased by 4 times and 3.3 times,respectively.Fe was vapor-deposited into a film by vacuum evaporation to realize spin injection of holes,and a device structure of ITO/Fe（y=0 1 2 3nm）/MoO₃（5nm）/NPB（60nm）/Alq₃（80nm）/Cs Cl（0.5nm）/Al（120nm）organic spin electroluminescent devices have played a significant positive role in improving device performance.In the absence of a magnetic field,when the thickness of the Fe film is1 nm and the bias voltage is 9 V,the light emission brightness of the device reaches 48650cd/m².Compared to the undoped device,the brightness is improved by 25%.Under the modulationof the magnetic field,the magnetic conductance（MC）and magnetoluminescence（MEL）of the undoped device increase rapidly and then become saturated,while the MC and MEL of the doped device have been increasing as the magnetic field increases.Out of saturation state,and the MC value of the doped device is nearly 5 times higher than undoped device.The difference between the doped device and the undoped device can be attributed to the spin polarization of the holes by the ferromagnetic metal.The spin-orbit coupling results in the quenching of triplet excitons and the increase in the rate of singlet excitons.This makes the device performance improved.