Research And Preparation Of Efficient Inverted Organic Electroluminescent Devices

Organic light emitting diodes(OLED)have been considered to be the next generation flat panel display technology due to the advantages of high efficiency,high luminance,low power consumption,wide view angle,fast swift,ultra-light weight and flexibility which shows tremendous application prospect.Compared with traditional OLED structure,inverted OLEDs can directly connect with mainstream n-channel thin film transistor backplane,which is beneficial to achieve high resolution and large size display panel.However,there are some challenges to achieve high performance in inverted OLEDs,such as electron injection and light out-coupling of the devices.In this thesis,we mainly investigated the interface modification of electron injection layer and the influence of quasi-periodic nanostructures in inverted OLEDs.This thesis includes the following aspects:(1)The sol-gel ZnO was chosen as electron injection layer in inverted OLEDs,PEI solution was used to preliminary modify the ZnO thin films,and then a n-doped Cs2CO3:Alq3 layer was used for further modification.Eventually,the work function of ZnO was reduced from 4.0 eV to 2.7 eV,the barrier between ZnO and organic electron transporting layer was largely reduced which can achieve high efficient electron injection.(2)Quasi-periodic nanostructures can largely enhance light extraction efficiency in OLEDs.By using soft nanoimprinting technology,we fabricated dual-imprinted ITO-Glass substrate by combining quasi-periodic nanostructure with ZnO thin film.Eventually,the total transmittance was enhanced from 86%to 93%and responded at broad light spectrum at the same time.(3)The surface modification in electron injection layer and light extraction technology have been applied in phosphorescent green OLEDs.Through surface modification,the open voltage of green OLEDs was reduced from 8 eV to 3.5 eV,and device performance was significantly enhanced.Furthermore,the nanostructured phosphorescent green OLEDs was fabricated,and yielding external quantum efficiency(EQE)of 31.7%and current efficiency of 121.3 cd A-1 which reached 2.23 times and 2.24 times compared to the conventional flat devices.(4)We fabricated inverted white OLEDs with quasi-periodic nanostructures,and studied their optical and electrical characteristics,yielding highest external quantum efficiency(EQE)of 42.4%,current efficiency of 118.4 cd A-1 and power efficiency of 85.4 lm W-1,which is 2.15 times,2,22 times and 2.1 times to the flat device.Lastly,the FDTD optical simulation was conducted to analysis energy flux distribution in white OLEDs after using quasi-periodic nanostructures and elaborated light manipulation mechanism in detail.