Research On All Solution-Processed Flexible OLED And Its Device Performance

Organic light-emitting diode(OLED)is one of the most promising technologies for the next-generation high-performance displays,because of its large color gamut,thin and light structure,high efficiency and low energy consumption.The solution-processed method has attracted more and more attention in the academia and industry community of OLED,due to the characteristics of low cost,large area,high material utilization,and compatibility with roll-to-roll process.However,the solution-processed method faces the re-dissolving problem between adjacent layers,which makes it difficult to prepare multilayer device structures with small energy differences.In addition,high-resolution OLED display is mainly realized by the traditional photolithography technology,which is highly dependent on the expensive equipment.In this thesis,a facile electrode patterning method is developed,a high-performance light-emitting ink with three organic hosts is studied,and finally all solution-processed OLED is fabricated.The specific research content are as follows:(1)A rapid patterning method for highly conductive poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid)(PEDOT:PSS)electrodes.The conductive polymer PEDOT:PSS has the advantages of high transmission,adjustable conductivity,and good solution processability,which makes it a promising electrode material for optoelectronic device application.However,the low conductivity(0.16 S/cm)of the pristine PEDOT:PSS and its strongly acidic nature affect the performance of conventional photoresists,hence it is urgent to develop a new patterning method of PEDOT:PSS.In this chapter,hexa-2,4-diyne-1,6-diol(HDD)with a photopolymerization ability is used,and the modified PEDOT:PSS film obtains the photopattern ability after adding HDD.Meanwhile,it is found that the addition of HDD can promote the phase separation of PEDOT:PSS and the configuration transformation of PEDOT group from benzene to quinone,leading to an enhancement in the electrical conductivity(up to 627 S/cm).Finally,flexible OLEDs are fabricated based on the patterned PEDOT:PSS electrodes,obtaining a luminance of 34210cd/m~2 and a current efficiency of 28.90 cd/A.(2)Highly efficient organic light-emitting diodes based on three hosts and phosphorescent dopant.In order to avoid re-dissolving problem between adjacent layers in solution-processed OLEDs with a multilayer structure,we propose a three-host system with bipolar transport ability,including hole-transporting PVK with good film-forming ability,electron-transporting OXD-7 with good solubility,and PO-T2T with high electron mobility.It is found that PVK and PO-T2T can form a charge transfer state,which is beneficial to the carrier injection and host-guest energy transfer,resulting in the improved device efficiency.Finally,combined with the optimized Ca/Al cathode,the solution-processed OLED with a monolayer sandwich structure achieves a current efficiency of 49.16cd/A.(3)All solution-processed flexible OLEDs.In this chapter,the top electrodes of OLEDs are prepared by stamp transfer and direct spraying methods.Firstly,the AgNWs top electrodes are patterned owning to the surface energy difference of PDMS substrate caused by UVO treatment.The patterned AgNWs electrode has a thickness of 1μm and a low surface resistance of 46Ω/sq.However,the AgNWs top electrode could not be compactly bonded to the light-emitting layer,due to the large surface energy difference between the AgNWs electrode and the light-emitting layer,resulting in the failure of all solution-processed OLEDs.Further,the direct spraying method is explored to prepare AgNWs top electrode on the light-emitting layer.The effect of spraying distance and spraying time on the performance of AgNWs top electrode is studied.Subsequently,a translucent AgNWs top electrode with a thickness of 180 nm,a transmittance of 63%,and a surface resistance of 12Ω/sq is obtained.It was also found that the light-emitting layer would not be damaged during the rapid spraying process of AgNWs top electrode.Finally,the translucent flexible OLEDs are prepared by the all solution-processed method consisted of the patterned PEDOT:PSS bottom electrode,the organic light-emitting layer,and the sprayed AgNWs top electrode.In this thesis,HDD is used to enable the PEDOT:PSS electrode with patterning capability while the conductivity is significantly enhanced,the PVK:OXD-7:PO-T2T three-host system is developed to simplify the device structure and avoid the re-dissolving problem during multilayer preparing processing,and the spraying process of AgNWs top electrode is developed to realize the transparent flexible OLEDs.This study proposes a facile method of all solution-processed OLEDs with patterning electrodes,which will shed light on the future development of all solution-processed flexible OLEDs.