Research On Flexible Organic Light-emitting Diodes Based On Modified PEDOT?PSS Electrode

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid)(PEDOT:PSS)electrode has excellent photoelectric and mechanical properties,and it is often used as a flexible transparent electrode in the photoelectric field.However,when the PEDOT:PSS electrode is applied to a flexible organic light-emitting diode(OLED),the PEDOT:PSS electrode has a low adhesion to the flexible substrate,which makes the flexible OLED device poor in bending resistance.In addition,due to the presence of sulfonic acid groups in the PEDOT:PSS electrode,the PEDOT:PSS(p H:1.5-2.5)electrode is acidic and hygroscopic,which will adversely affect the efficiency and life of the device.In this thesis,modified PEDOT:PSS electrodes are applied to flexible OLEDs to explore the application potential,existing problems and development prospects of PEDOT:PSS electrodes in them.We use doping to improve the adhesion of the PEDOT:PSS electrode to the flexible substrate,and use surface modification and doping to reduce the acidity of the PEDOT:PSS electrode,which improves the air stability and adhesion of the PEDOT:PSS electrode and alleviates the damage caused by acidic PEDOT:PSS electrodes to the efficiency and lifetime of flexible OLEDs.The specific research content is as follows:(1)The preparation of highly conductive PEDOT:PSS film and D-sorbitol modification enhance the flexibility of the film.In order to improve the conductivity and quality of the PEDOT:PSS transparent conductive electrode(TCE),we added 2-(2-[4-(1,1,3,3-Tetramethylbutyl)phenoxy]ethoxy)ethanol(Triton X-100)to the PEDOT:PSS solution and prepared it on a flexible substrate by spin coating.In addition,we used dimethyl sulfoxide(DMSO)doping and ethyleneglycol(EG)post-treatment to reduce the sheet resistance of the PEDOT:PSS film to 74.6?/?.Based on the above work,we added D-sorbitol to the modified PEDOT:PSS solution to improve the adhesion of the PEDOT:PSS film to the flexible substrate.After 3000 bends(radius of curvature r=4 mm),the sheet resistance of modified PEDOT:PSS film had increased by only 20%.Finally,we prepared a flexible green OLED device based on the modified PEDOT:PSS film.The performance of the device showed that the current efficiency and power efficiency of the flexible OLED device doped with D-sorbitol were from20.5 cd/A and 6.4 lm/W to 38.9 cd/A and 14.3 lm/W,respectively.Compared with the reference device,the D-sorbitol doped device still maintained 50%of the initial brightness after 300 bends(r=4 mm)(reference device L/L_o was 20%).(2)Polyethyleneimine ethoxylated(PEIE)surface modification improves the air stability of PEDOT:PSS film.In order to reduce the acidity of the PEDOT:PSS electrode,we used PEIE to modify the surface of the modified PEDOT:PSS film on the base of the first part of the research work.The cross-linking reaction occurred between them,which reduced the acidity of the PEDOT:PSS electrode surface and improved the flexibility and air stability of the PEDOT:PSS electrode.Finally,we prepared a flexible green light OELD device based on PEIE modified PEDOT:PSS electrode.Because PEIE improved the carrier balance,the current efficiency and power efficiency of the device were increased from 20.5 cd/A and 6.4 lm/W to 76.4 cd/A and 21.8 lm/W,respectively,which were 3.7 times and 3.4 times higher than those of the unmodified device.(3)Basic amino acids regulate the p H value of PEDOT:PSS.In order to improve the life of flexible OLED devices,we further added basic amino acids(arginine,lysine,histidine)to the PEDOT:PSS solution on the base of the first and second part of the work.By adjusting the solution near the neutral(p H=7),the damage of PSS to the efficiency and lifetime of OLED devices in PEDOT:PSS solution can be alleviated,which made PEDOT:PSS film can be used as a hole injection layer.On this basis,we prepared a flexible green OLED.It is found that the lifetime of the corresponding OLED was improved after the PEDOT:PSS solution was doped with arginine and lysine,and the lifetime of the lysine-doped flexible OLED device was doubled from 28 min to57 min.Finally,DMSO was added to the lysine-doped PEDOT:PSS solution to improve its conductivity,whicn was used as a hole injection layer.Compared with the standard device,the current efficiency and power efficiency of the device were increased from42.6 cd/A and 19.7 lm/W to 70.4 cd/A and 36.8 lm/W,respectively.In this thesis,the doping of D-sorbitol effectively improved the flexibility and surface wettability of PEDOT:PSS film,which improved the device efficiency of OLED.At the same time,through the use of PEIE surface modification and basic amino acid doping,the damage caused by the sulfonic acid group in the PSS to the efficiency and life of the flexible OLED device was effectively alleviated.Our work has developed some new methods for optimizing PEDOT:PSS electrodes,which provides some references for the commercial application of organic light-emitting devices based on PEDOT:PSS electrodes.