Fabrication And Investigation Of OLED Devices Based On ESIPT Luminescent Materials With High Exciton Utilization And Their Properties

White Organic Light Emitting Diodes(WOLEDs)have a wide range of applications in modern industrial scenarios and daily life,with great prospects in full color displays,solid-state lighting,and large-scale applications,due to many advantages such as low energy consumption,light weight,flexibility,and ultra-thin thickness.Therefore,WOLEDs have received widespread attention from both academic and scientific communities.Among them,conventional WOLEDs based on energy transfer(ET)mechanism simplify the device manufacturing process.However,due to the difficulty in accurate control of the ET process,the device fabrication lacks the spectrum stability and manufacturing repeatability.This greatly limits large-scale production of WOLEDs.Thus,it is anticipated that non-energy transferred WOLED has great potential to overcome these issues,due to their precise and controllable fabrication procedure.In addition,WOLEDs device efficiency has made great progress in recent years.The "hot exciton" OLED light-emitting materials can well balance the high device performance and efficiency roll-off well through the rapid reverse intersystem crossing(RISC)from the high-lying triplet state.In this thesis,we have developed the excited state intramolecular proton transfer(ESIPT)fluorophore Py HBT with typical "hot exciton" characteristics.Its single-emitter yellow OLED exhibits a high external quantum efficiency(EQE)of 5.64%,a max current efficiency(CE)of 16.81cd/A and a max power efficiency(PE)of 17.29 lm/W.To date,this is among the highest performance of yellow emitting ESIPT fluorophores.Through deep study of electroluminescence mechanism,we find that the ESIPT material has a typical "hot exciton" characteristic and the efficient utilization of high-energy triplet state excitons by fast RISC from high triplet state state to singlet state accounts for the high device performance.On this basis,the traditional thermally activated delayed fluorescence(TADF)blue emitters are mixed with the yellow ESIPT material with a large Stokes shift to form non-energy-transfered white-emitting thin films with complementary color.Without interference of energy transfer,high-performance WOLEDs have been demonstrated to exhibit high repeatability,high device efficiency,and good color stability.By independent use of nearly 100% of excitons in both emitters and expanding the exciton recombination region,the complementary-color WOLED based on Py HBT and DMAc-MPM showed a maximum EQE of 14.30%.These results indicate that the blue and yellow light materials in this type of WOLED device can independently utilize low energy level and high energy level reverse intersystem crossing in TADF and ESIPT hot exciton emitters without being affected by energy transfer,which achieves highly efficient utilization of singlet excitons and thereby high device efficiency.More importantly,these non-energy-transfered WOLEDs also present high reproducibility and good color stability.This paves way for high-yield and large-scale production of low-cost and efficient WOLEDs.