以BAlq为主体的高效高色纯度的红色有机电致磷光器件

以铱配合物红色磷光体Ir(piq)₂(acac)为掺杂剂,制备了基于BAlq材料的红色电致磷光器件,其结构为ITO/NPB(30nm)/Ir(piq)₂(acac):BAlq(25nm)/BCP(13nm)/Alq₃(35nm)/LiF(1nm)/Al(1000nm),当掺杂浓度为8%的时候,器件发光的色坐标为(x=0.67,y=0.32),基本满足了全色显示对红色发光的要求。在电压为16V时,器件达到最高亮度9380cd/m²。在电流密度为5.45mA/cm²时,外量子效率达到最大5.7%。由于磷光体Ir(piq)₂(acac)的磷光寿命较短,所以器件在高电流密度下,仍然保持较高的外量子效率。电流密度为100mA/cm²时,外量子效率仍然维持在4.7%。进一步研究表明在器件中短程的Dexter能量传递以及红光染料对空穴的直接捕获两种机制同时存在。

High Efficiency and High Color Purify Red Organic Electrophosphrescent Devices Using BALq as Host Material

Intense research activities are currently being undertaken on organic light-emitting devices.Because of their potential applications in flat panel displays and solid state lightening.Light-emitting materials for these devices can be divided into two general classes,those are fluorescent and phosphorescent materials. Phosphorescent light emitting devices are particularly interesting for being able to utilize all the injected charges for emission.Heavy-metal complexes in which strong spin-orbit coupling leads to singlet-triplet state mixing can result in high efficiency electrophosphorescence in organic light-emitting devices(OLEDs).In this report, devices using red phosphorescent dye Ir(pig)2(acac) as dopant and BAlq as host are fabricated.The structure of the device is ITO/NPB(30 nm)/Ir(piq)₂(acac):BAlq(25 nm)/BCP(13 nm)/Alq₃(35 nm)/LiF(1 nm)/Al(1000 nm). All of the films are fabricated by thermal deposition way onto a precleaned ITO-coated glass substrate (sheet resistance 50 Ω/□) at a background pressure <2×10^-4 Pa. The deposition appartus is Edward Auto-500 Thermal Evaporation Coating System.The thinkness of the deposited films is monitored by an oscillating quartz thickness monitor.The electroluminescence(EL) spectra, brightness and CIE coordinates of the devices are recorded with Spectra Scan PR-650(Photo Research).The brightness-current density,voltage versus current density are measured by a OLEDs testing system,comprosing of a 2400 Sourcemeter(Keithley) and a 485 Picoammeter(Keithley).All the measurements are carried out at room temperature.We change the doping concentration in the host material.When the doping concentration reaches 8%, the commission internationale de’Eclairage (CIE) coordinates of the device are (x=0.67,y=0.32), which are close to meet video display standards.The device reaches the highest brightness 9 380 cd/m² at voltage 16 V. The external quantum efficiency reaches 5.7% at the current density 5.45 mA/cm².Because of the short phosphorescent life of the Ir(piq)₂(acac),the external quautum efficiency is still as high as 4.7% at the current density of 100 mA/cm².Futher study shows that both the short range Dexter energy transfer mechanism and the direct dopant dye trap exist simultaneously.