使用复合色转换膜结合蓝绿有机发光器件实现高质量白光发射

High-quality White Light Emission by Blue-green Organic Light Emitting Devices with Hybrid Color-conversion Layer

采用(E)-4-二腈亚甲基-2-叔丁基-6-(1,1,7,7-四甲基久洛尼定乙烯基)吡喃(4-(Dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidin-4-yl-vinyl)-4H-pyran,DCJTB)分散到PMMA中作为色转换膜(CCL),分别结合纯蓝光和蓝绿光器件为激发光源制备得到了白光有机发光器件(WOLED)。研究结果表明,使用发光层结构为mCP∶Firpic(10 nm)/mCP(1 nm)/mCP∶4CzIPN(1.5 nm)的蓝绿光器件作为激发光源时,制备得到的WOLED性能明显优于使用纯蓝光进行激发的WOLED性能,其最大电流效率(CE)为15.44 cd/A、显色指数(CRI)77、色坐标(0.3206,0.3695)、色转换效率(CCE)52%。为了进一步展宽电致发光(EL)光谱并提高CRI,将DCJTB和无机荧光粉Sr_(2)Si_(5)N_(8)∶Eu^(2+)按一定比例混合后分散到PMMA中,制备得到复合CCL并将其以不同的速率旋涂到蓝绿光器件背面。结果表明,掺入Sr_(2)Si_(5)N_(8)∶Eu^(2+)后白光OLED的CRI获得明显改善,这是由于通过对CCL厚度的调控,使得掺杂后CCL的红光峰逐渐红移从而引起EL光谱更进一步地展宽;并且当旋涂速率为750 r/min时,获得的WOLED具备最佳的CCL厚度及EL性能,其最大CE、CRI、色坐标、CCE分别达到11.29 cd/A、82、(0.3206,0.3695)和34%。

The white organic light emitting diodes(OLEDs)were fabricated by employing DCJTB dispersed in PMMA as a color conversion layer(CCL)and pure blue and blue-green OLEDs as excitation sources.The results showed that the electroluminescence(EL)performance of the white OLED(WOLED)employing the blue-green OLEDs as the excitation source with the emitting layer structure of mCP∶Firpic(10 nm)/mCP(1 nm)/mCP∶4CzIPN(1.5 nm)was significantly better than that of the WOLEDs with the pure blue excitation OLEDs,which demonstrated maximum current efficiency(CE)and color rendering index(CRI),CIE coordinate and color conversion efficiency(CCE)of 15.44 cd/A and 77,(0.3206,0.3695)and 52%,respectively.In order to further broaden the EL spectrum and increase the CRI,DCJTB and inorganic phosphor Sr_(2)Si_(5)N_(8)∶Eu^(2+) were mixed in a certain ratio and dispersed in PMMA to fabricate a hybrid material for CCL,which was spin-coated on the backsides of the blue-green OLEDs at various speed.The results showed that the dopant Sr_(2)Si_(5)N_(8)∶Eu^(2+) in the CCL will dramatically improve the CRI of the WOLED due to the broadening of the EL spectrum resulted from the red-shifting of the PL spectrum of doped CCL via the modulation of the CCL thickness.The WOLEDs with the optimal doped CCL thickness reveal optimal EL performance with the respective maximum CE,CRI,CIE coordinate and CCE of 11.29 cd/A,82,(0.3206,0.3695)and 34%,respectively,at the spin speed of 750 r/min.