Abstract
Although solution-processible polymer-based light-emitting diode (PLED) is structurally simple and cost-effective, its efficiency is still far below small molecular light-emitting diode (OLED). The bottleneck to high efficiency is that solution processing itself causes intermixing between spin-coated polymer layers. Various techniques were developed to avoid intermixing and allowed for the fabrication of multilayered polymer structure. My research goal is to study how to design highly efficient blue and white PLEDs. My research is based on buffer layer technique previously developed in our Lab. We test the integrality of multilayer structure by checking the total film thickness and observing the performance of devices. We found that this buffer layer technique could be a general and reliable method to fabricate multilayer PLED. Then we introduce hole blocking-layer (electron- transporting layer), electron-blocking layer (hole-transporting layer) into double-layer and triple-layer structures. With our optimization by adding an electron-blocking layer, the external quantum efficiency (EQE) of blue PLED can be increased from 1.5% to 4.2% (from 2.7cd/A to 7.3cd/A) which is closed to the theoretical limit. The EQE of white PLED based on this highly efficient blue PLED reaches 2.4%, and the luminance is over 20000cd/m2.