Fabrication And Application Of Nanostructured Flexible Substrates For Light Emitting Devices

Organic light emitting diodes(OLEDs)have attracted enormous attention due to their favorable properties,such as low cost,high brightness,broad viewing angle and implementability of flexible display.However,the energy extracted from the device is limited to 18%due to the existence of metal loss,surface plasmon loss,waveguide mode and substrate mode,according to the photon loss mechanism in planar oleds.In order to improve the light out-coupling efficiency of devices,people apply light extraction methods,for instance,using microlens,introducing nanostructures in functional layers.Nonetheless,when the same experiment conditions are applied in constructing flexible devices,there may be much difficulty and damage to device performance.In this paper,we put forward a method based on flexible PET substrates and polystyrene sphere arrays to get nanostructured curved substrates.We prepared polystyrene sphere arrays by self-assembly methods on PET substrates,which were then treated by reactive ion etching(RIE).During RIE process,PS spheres reacted with oxygen and turned smaller,letting PET substrate be exposed to oxygen plasma.Finally,we can get substrate with regular nanostructure by further reaction between oxygen and PET,and we can also control the depth of nanostructure by controlling etching time.Based on the flexible substrate mentioned above,we introduced MDCE electrodes and produced green fluorescent device.The results showed the effectiveness of external light out-coupling technology.The current efficiency and power efficiency of device have 1.30 fold and 1.38 fold improvement,respectively.Besides,we also try to fabricate efficient inverted quantum light emitting devices based on sol-gel zinc oxide films.In future plan,we want to fabricate highly efficient flexible QLED which is based on such substrates and transparent electrodes.The method to obtain flexible nanostructured substrates have advantages of easy fabrication,highly controllable,low cost and it is suitable for both internal and external out-coupling.It is hopeful for us to extend the application of this kind flexible nanostructured substrates to get high-efficiency light emitting devices in the future.