Research On Problems And Solutions Of Electrochemical Polymerization Films In Organic Electroluminescence Display Application

Recently,organic light emitting diodes(OLEDs)based display has attracted much attention due to its broad application prospects in flexible display field.OLEDs usually require light-emitting diodes to be fabricated on a patterned electrode substrate.Electrochemical polymerization is an effective method to prepare electroactive conductive polymer films.The electrochemical deposition of the organic layer on the electrode is spontaneously selected,which effectively reduces the position error.Electropolymerized films are usually chemically cross-linked and are insoluble in common solvents,which is conducive to the preparation of multilayer optoelectronic devices.Our research group has developed an electrochemical cross-linking polymerization technology based on carbazole,and successfully fabricated double-layer electropolymerized films based electroluminescent device on an ultra-high resolution substrate.The introduction of an electrochemically cross-linked hole transport layer is beneficial to improve the hole transport capacity of the device and the film quality of the electropolymerized light-emitting layer,thereby improving the performance of the light-emitting device.However,there are still some problems in the application of electropolymerized technology in OLEDs,including how to improve the quality of electropolymerized films and how is it compatible with metal electrode substrates.The thesis focuses on the problems and solutions in the application of electrochemical polymer films in organic electroluminescence displays.It mainly includes the following three aspects:Firstly,adjustment of carbazole polymerization activity and film quality.The effect of electrolyte viscosity on the electrochemical reaction kinetics and electropolymerized mechanism of precursor molecules was studied.An electropolymerized mechanism was proposed,which was different from that of carbazole derivatives such as monocarbazole and alkyl carbazole,that is,TCTA monomer preferred to polymerize at 3 and 6 positions of carbazole group in higher viscosity solution.It is beneficial to obtain high cross-linking degree and density of TCTA electropolymerized films.The TCTA electropolymerized film was applied as the hole transport layer in the array pixel light-emitting device to prepare the PM monochromatic display device with uniform light and clear boundary.The introduction of the hole transport layer not only improves the hole mobility and conductivity of the light-emitting device,but also improves the redox reversibility during the electrochemical polymerization of the OCBz C light-emitting layer.The unreacted suspended carbazole of TCTA electropolymerized film can be used as the nucleation site of OCBz C.Secondly,the electrochemical polymerization top-emitting device.The redox behavior and electrochemical stability of the common metal full-emitting layer during the electropolymerized process were studied.The Al/ITO with better stability was selected as the anode of the top-emitting OLED device,and the TCTA electropolymerized film was used as the hole transport layer.The thickness of the anode layer and the electropolymerized film was optimized,and the electrochemical top-emitting OLED device was successfully prepared.The maximum brightness of the electrochemical top-emitting OLED device based on the P-PPV light-emitting layer was 3312 cd m^-2,and the maximum current efficiency was 3.32 cd A^-1.Different emission colors can be obtained by adjusting the thickness of the electropolymerized organic layer.When the thickness of the TCTA electropolymerized film changed from 20 nm to 68 nm,the peak position of the electroluminescence spectrum of the top-emitting OLED device was red-shifted from 550 nm to 602 nm,the emission color changed from yellow-green light to orange-red light.Thirdly,electrochemical doping and film quality.Potentiostatic doping technology was used to improve the hole mobility and electrical conductivity of electropolymerized films.Compared with the undoped film,the conductivity of the doped film increased,and the hole mobility was 2 orders of magnitude higher than that before doping.Different doping potentials will also cause changes in the hole mobility of the doped film.The highest mobility was 4.15×10^-4 cm² V^-1 s^-1 when the doping potential was 0.9 V,which was 273 times that of the film before doping.The doped TCTA electropolymerized film was applied to the hole transport layer of the light-emitting device.Compared with the undoped film device,the doped film device had a lower turn-on voltage,an increase in brightness,and a current efficiency level close to that of the undoped film device.And when the thickness of the electropolymerized film increased,the brightness of the doped film device decreased slowly(the brightness was reduced by 38.3%,and the brightness of the undoped thin film device was reduced by 73.2%),which was more suitable for the preparation of high-thickness film devices.