基于器件结构提高TADF-OLED器件的发光性能

为了提高以TADF材料作为主体、天蓝色荧光材料作为客体的混合薄膜的OLED器件光电性能,我们调整了器件结构,使主体材料发挥其优势。制备了基本结构为ITO/NPB(40 nm)/DMAC-DPS∶x%BUBD-1(40 nm)/Bphen(30 nm)/LiF(0.5 nm)/Al的OLED器件。研究了主-客体材料在不同掺杂浓度下的OLED器件的光电特性。为了提高主体材料的利用率,在空穴传输层和发光层之间加入10 nm的DMAC-DPS作为间隔层;然后,在阳极和空穴传输层之间加入HAT-CN作为空穴注入层,形成HAT-CN/NPB结构的PN结,有效降低了器件的启亮电压(2.7 V)。测量了有无HAT-CN的单空穴器件的阻抗谱。结果表明,在最佳掺杂比例(2%)下,器件的外量子效率(EQE)达到4.92%,接近荧光OLED的EQE理论极限值;加入10 nm的DMAC-DPS作为间隔层,使得器件的EQE达到5.37%;HAT-CN/NPB结构的PN结有效地降低了器件的启亮电压(2.7 V),将OLED器件的EQE提高到5.76%;HAT-CN的加入提高了器件的空穴迁移率,降低了单空穴器件的阻抗。TADF材料作为主体材料在提高OLED器件的光电性能方面具有很大的潜力。

Enhanced Luminescent Properties of TADF-OLEDs Based on Device Structures

In order to improve the optoelectronic properties of organic light emitting diodes(OLEDs)with a hybrid film as the light emitting layer,which included the thermally activated delayed fluorescent(TADF)as host matrix and the sky-blue fluorescent material guest,we adjusted the device structures properly to improve the utilization rate of the host material.The basic structure of OLED is ITO/NPB(40 nm)/DMAC-DPS∶x%BUBD-1(40 nm)/Bphen(30 nm)/LiF(0.5 nm)/Al.First,the optoelectronic properties of host-guest OLED devices was studied with different doping ratio.Then,the DMAC-DPS(10 nm)was evaporated between the hole transport layer and the emission layer,it improved the utilization rate of the host material.Moreover,an organic material HAT-CN was added as the hole injection layer between the anode and the hole transport layer with the method of vacuum evaporation.Finally,the hole-only devices with or without HAT-CN were fabricated for the impedance spectra.The results indicated that the external quantum efficiency(EQE)of 4.92%was acquired at the optimal doping ratio(2%),it approached the theoretical EQE limit of the fluorescent OLEDs.The DMAC-DPS(10 nm)between the hole transport layer and the emission layer improved the utilization rate of the host material,led to a higher EQE of 5.37%,and breaked the limit of 5%of the EQE of traditional fluorescent OLEDs.The HAT-CN/NPB heterojunction units effectively reduced the driving voltage of OLEDs(2.7 V),and the maximum EQE increased to 5.76%at the same time.Additionally,From the lg J-lg V curves and the impedance spectrum analysis,the hole-only devices with HAT-CN improved the hole mobility and reduced the impedance of the devices.This study shows that TADF materials have great potential in enhancing the optoelectronic performance of OLEDs.