Study On Optical Manipulation Of Micro And Nanostructures In Flexible Organic Light-emitting Diodes(FOLEDs)

Recently, the products of wearable electronics have been into the market one by one, such as smart watches and wrinkles, also including bendable OLED displays and lightings, mainly represented by LG Display and LG Chemistry. So it is very clear that FOLEDs are gradually gaining popularity among consumers. FOLEDs are defined by fabricating OLED devices on plastic substrates, like PET, PC and PEN to replace traditional glass-based devices. Compared with liquid crystal displays(LCDs) and LEDs, FOLEDs/OLEDs are highlighted due to the flexibility of the organic materials apart from other advantages, self-lighting, broadband emission and light weight. However, instead of output yield, there still exists some bottlenecks for promoting FOLEDs/OLEDs market, mainly focusing on increasing device efficiency and stability. Therefore, there is much space left for us to expand for FOLED research and manufacturing, how to incorporate out-coupling nanostructures more simply, how to prolong operational life of OLED etc. Here our work put the attention into induction of nanostructures and modification for hole injection layer(HIL), respectively, and finally get a remarkable increase in the light extraction efficiency and device stability.My work is as detailed follows,1. Solution-processed MoOx:Au NPs inter-layer is incorporated into OLED device as a composite HIL by spin-coating. MoOx:Au NPs inter-layer is composed of the mixture of solution-processed precursor of MoOx and Gold nanoparticle(Diameter of 20 nm), which is made by citric acid method. The OLED structure is simple sandwich of ITO/MoOx:Au NPs/NPB/Alq3/LiF/Al, which utilizes reliable work function(WF) of MoOx and surface plasmonic effect of Au nanoparticles, realizing low turn-on voltage, high efficiency and good stability in our OLED devices.2. By utilizing soft imprinting(SIP) technique, we have successfully incorporated quasi-random moth-eye nanostructure into HIL of PEDOT:PSS of FOLED devices. Compared with 1-D grating and 2-D grating, also fabricated by SIP method, the quasi-random nanostructure can bring remarkable increase in efficiency and emission & spectra stability from varying viewing angles, while periodic gratings usually have wavelength limitation and lead to angle-dependent in EL spectra, due to their bragg diffraction effect.3. Based on our previous work, which is about modification on HIL of PEDOT:PSS in FOLEDs, here we consider using high conductive PEDOT:PSS(H-PEDOT:PSS) as anode to realize ITO-free FOLEDs. And nanostructured UV/PET is consider as our FOLED device substrate. According to paper reports, the conductivity of H-PEDOT:PSS can be further increased by adding crosslink additives and conducting post-treatment. And the conductivity can go as high as 2500 S cm-1, reported by Ouyang’s group. However, due to the wettability of PEDOT:PSS, its stability affects the conductivity seriously and then affect the device performances. In our experiments, the nanostructured UV based FOLED device is compared with the flat one, and we find that there is obvious increase in device efficiency with out-coupling UV nanostructures. But it is still a problem for the device stability and we will optimize the experiment condition in our further work.