环境湿度对有机电致发光二极管功能材料的影响∗

摘要

随着有机电致发光二极管(OLED)市场化进程加快,有机光电功能材料的应用日趋广泛,但环境湿度对 OLED功能材料影响的研究鲜有报道.以典型的空穴传输材料 N,N′-bis-(1-naphthyl)-N,N′-biphenyl-1,1′-biphenyl-4,4′-diamine(NPB)为例,将其分别置于环境湿度为5％,20％,35％和50％,环境温度均为25℃的条件下24 h,以其为空穴传输层构建绿色荧光 OLED器件；系统调查了NPB材料不同存储环境湿度对 OLED器件性能的影响.结果表明,随着NPB存储环境湿度不断增加(5％~50％),器件性能逐渐降低,其中最大电流效率由3．96 cd/A降低到3．31 cd/A.进一步地,单载流子器件的电流-电压特性表明,随着环境湿度的增加,NPB空穴传输性能逐渐增强,这加剧了 OLED器件中空穴和电子传输性能的不平衡,导致器件效率较低.此外,分析了 NPB薄膜光致发光(PL)光谱随着材料存储湿度的增加逐渐红移的现象,这可能是由于水分子的侵入,使得 NPB分子的局域激发态转换为具有强烈电荷转移特征的激发态的结果.%With accelerated marketization process of the organic light-emitting diode (OLED),organic optoelec-tric functional materials were more widely applied.However,the research results about the effect of environ-mental humidity on OLED functional materials were rarely reported.A typical hole-transporting material,N, N′-bis-(1-naphthyl)-N,N′-biphenyl-1,1′-biphenyl-4,4′-diamine (NPB)was taken as an example to investigate the humidity effect on the photoluminescent properties of organic materials and electroluminescent performance of and OLED devices.The NPB material was stored in various controlled relative humidity (RH)values at 5%, 20%,35% and 50% at 25 ℃ for 24 h.OLED devices were fabricated with the NPB as hole-transporting layers and tris(8-hydroxyquinoline)aluminium (Alq3 )as light emitting layer.The effect of environmental humidity on the performance of OLED was studied.The results indicated that the performance of OLED was progressively decreased with increasing humidity ranging from 5% to 50%,and the maximum current efficiency reduced from 3 .9 6 to 3 .3 1 cd/A.Furthermore,current density-voltage characteristics of the hole-only devices presented that the hole mobility of NPB was increased with increasing humidity,which resulted in poor charge balance.The photoluminance spectra of the NPB film exhibited obvious red-shift with increasing the material storage humidi-ty,which may due to the excited states from the locally excited state to an excited state with the strong charge transfer character.