白色磷光电致发光器件效率提高的研究
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摘要
有机电致发光器件(OLED)具有视角宽、高亮度和高色稳定性等优势,故使之倍受瞩目。有机磷光电致发光器件与普通有机荧光器件相比具有更高的亮度和效率,是OLED的一个重要发展方向。近年来,由于白色有机电致发光器件(WOLED)可结合彩色滤色膜技术实现全色显示,同时也可作为液晶背光源和固态照明光源,其商业化前景非常诱人,已经引起人们的广泛兴趣。所以研究和发展白色磷光有机电致发光器件具有特殊的意义。
本文围绕白色磷光有机电致发光器件的制备及其性能的提高展开深入研究,做了如下几方面的工作:
1.以宽带隙的聚合物PVK为主体材料,分别掺入蓝色荧光染料N-BDAVBi,红色磷光染料Ir(piq)2(acac)和绿色磷光染料Ir(ppy)_3,制成多重掺杂单发射层WOLED。这里采用Ir(ppy)3作为磷光敏化剂,通过多组实验结果的对比,最终确定了最佳染料掺杂浓度和器件结构,得到最佳色坐标为(0.33,0.38),已位于CIE1931色度图的白色等能区之内,器件的亮度为4464cd/m~2 ,外量子效率为0.92% ,比无Ir(ppy)_3做敏化剂的器件外量子效率提高了很多。同样以聚合物PVK为主体材料,分别掺入蓝色荧光染料N-BDAVBi,红色磷光染料Ir(piq)_2(acac)和高效橙红色荧光染料(Rubrene),这里Rubrene用来调整其白光发光色度,从而制备出具有单一发光层结构且发纯白色光的OLED器件,并对这种掺杂型白光器件的发光及电学性能进行了深入的研究和探讨。
2.采用高效磷光染料Ir(piq)2(acac)作为发光掺杂剂,掺入空穴传输型主体材料NPB中,得到红色发光层,荧光材料TBPe掺入到主体CBP中作为蓝色发光层,制备了结构为ITO/NPB/NPB:Ir(piq)2(acac)/CBP/CBP:TBPe/BCP/ALq/Mg:Ag的双发光层WOLED。在这里一方面红色磷光染料的引入可明显提高器件效率,另一方面可避免利用磷光染料获得蓝光层的器件寿命短的缺陷,使器件的整体性能得以优化而且双层掺杂型WOLED由于两发光层均为高浓度掺杂,因此器件制备过程相对简单。实验中通过适当调节发光层的掺杂比例和厚度,可以得到性能良好的白光器件。8V工作电压下器件色坐标和最大外量子效率分别为(0.33,0.30)和1.24 %,亮度在15V下高达7500 cd/m~2。
3.为了进一步提高双发光层器件的发光性能,我们选用高效荧光染料N-BDAVBi代替荧光材料TBPe ,将其掺入到双极性传输型主体材料CBP中得到蓝色发光层,磷光染料Ir(piq)_2(acac)掺入到主体BALq中作为红色发光层,同时用LiF/Al作为器件阴极,以增加电子注入,制备了结构为ITO/PVK:TPD/CBP: N-BDAVBi /CBP/ BALq: Ir(piq)_2(acac)/BCP/Alq_3/LiF:Al的双发光层白色有机电致发光器件。器件在8.6 V工作电压下的量子效率为6.78%,亮度在22 V下达25350 cd/m~2,并且在高亮度时器件的色坐标和电致发光光谱均无明显变化,具有很好的色稳定性。
4.分析了目前尚存在的问题和今后改进的措施和进一步工作的展望。
Organic light-emitting devices (OLEDs) have been attracting worldwide interest for their high efficiency, brightness and good colour stability. The brightness and efficiency of the devices have increased markedly with the introduction of phosphorescent materials than fluorescent materials,so this is an important direction of the development of OLED. Recently white organic light-emitting devices (WOLEDs) have drawn much attention due to their potential applications in full color displays, in backlight for LCDs, and in solid state lighting sources. Therefore the research and the development of WOLED has the special significance.
This paper revolved the fabrication and performance enhancement of WOLEDs and we have done the following work:
Firstly, by employing a polymer PVK as host material doped with fluorescent N-BDAVBi and phosphoresecent Ir(piq)2(acac)and Ir(ppy)_3 , the WOLED with a single light-emitting layer was fabricated successfully. Ir(ppy)_3 was used as a sensitizer. Its brightness reaches 4464cd/m~2 . CIE coordinates is (0.33, 0.38) .The devices show a maximum external efficiency of 0.92%which is higher than the device without Ir(ppy)_3.Then we made another type of single layer WOLED by using PVK: Rubrene:Ir(piq)_2(acac) :N-BDAVBi as light-emitting layer. The CIE coordinate of the device could be well controlled by Rubrene .
Secondly, by using a phosphorescent dye Ir(piq)_2(acac) as a red emitter and TBPe as blue emitter, We fabricated a double light-emitting layers WOLED . Its structure is ITO/NPB/NPB:Ir(piq)_2(acac)/CBP /CBP:TBPe/BCP/ALq/Mg:Ag. On one hand, the introduction of red phosphorescent enhance the efficiency, on the other hand, the blue fluorescent dye employed as blue emitting dye avoided the flaw of the short lifetime for blue phosphorescen and double doping layer devices have simple facture process because of their high doping concentration comparing with single doping layer .By adjusting the proportion and thickness of the dopants,We can get admirable white light. The devices show a maximum external efficiency of 1.24% with the CIE coordinates is (0.33, 0.30) at 8 V. The brightness reaches 7500 cd/m~2 at 15V.
Lastly,In order to improve the performance of double light-emitting device, we employ a high efficiency fluorescent dye N-BDAVBi instead of TBPe and LiF/Al is used as the cathode to enhance electrons injection.The bright and steady light emitting has been obtained.This OLED presents a maximum luminance of 25350cd/m~2 with CIE coordinates of (0.35, 0.35) at 22V and a maximum external quantum efficiency of 6.78% at 8.6V. The CIE coordinates vary slightly as the applied voltage changes from 6V to 22V.
本文围绕白色磷光有机电致发光器件的制备及其性能的提高展开深入研究,做了如下几方面的工作:
1.以宽带隙的聚合物PVK为主体材料,分别掺入蓝色荧光染料N-BDAVBi,红色磷光染料Ir(piq)2(acac)和绿色磷光染料Ir(ppy)_3,制成多重掺杂单发射层WOLED。这里采用Ir(ppy)3作为磷光敏化剂,通过多组实验结果的对比,最终确定了最佳染料掺杂浓度和器件结构,得到最佳色坐标为(0.33,0.38),已位于CIE1931色度图的白色等能区之内,器件的亮度为4464cd/m~2 ,外量子效率为0.92% ,比无Ir(ppy)_3做敏化剂的器件外量子效率提高了很多。同样以聚合物PVK为主体材料,分别掺入蓝色荧光染料N-BDAVBi,红色磷光染料Ir(piq)_2(acac)和高效橙红色荧光染料(Rubrene),这里Rubrene用来调整其白光发光色度,从而制备出具有单一发光层结构且发纯白色光的OLED器件,并对这种掺杂型白光器件的发光及电学性能进行了深入的研究和探讨。
2.采用高效磷光染料Ir(piq)2(acac)作为发光掺杂剂,掺入空穴传输型主体材料NPB中,得到红色发光层,荧光材料TBPe掺入到主体CBP中作为蓝色发光层,制备了结构为ITO/NPB/NPB:Ir(piq)2(acac)/CBP/CBP:TBPe/BCP/ALq/Mg:Ag的双发光层WOLED。在这里一方面红色磷光染料的引入可明显提高器件效率,另一方面可避免利用磷光染料获得蓝光层的器件寿命短的缺陷,使器件的整体性能得以优化而且双层掺杂型WOLED由于两发光层均为高浓度掺杂,因此器件制备过程相对简单。实验中通过适当调节发光层的掺杂比例和厚度,可以得到性能良好的白光器件。8V工作电压下器件色坐标和最大外量子效率分别为(0.33,0.30)和1.24 %,亮度在15V下高达7500 cd/m~2。
3.为了进一步提高双发光层器件的发光性能,我们选用高效荧光染料N-BDAVBi代替荧光材料TBPe ,将其掺入到双极性传输型主体材料CBP中得到蓝色发光层,磷光染料Ir(piq)_2(acac)掺入到主体BALq中作为红色发光层,同时用LiF/Al作为器件阴极,以增加电子注入,制备了结构为ITO/PVK:TPD/CBP: N-BDAVBi /CBP/ BALq: Ir(piq)_2(acac)/BCP/Alq_3/LiF:Al的双发光层白色有机电致发光器件。器件在8.6 V工作电压下的量子效率为6.78%,亮度在22 V下达25350 cd/m~2,并且在高亮度时器件的色坐标和电致发光光谱均无明显变化,具有很好的色稳定性。
4.分析了目前尚存在的问题和今后改进的措施和进一步工作的展望。
Organic light-emitting devices (OLEDs) have been attracting worldwide interest for their high efficiency, brightness and good colour stability. The brightness and efficiency of the devices have increased markedly with the introduction of phosphorescent materials than fluorescent materials,so this is an important direction of the development of OLED. Recently white organic light-emitting devices (WOLEDs) have drawn much attention due to their potential applications in full color displays, in backlight for LCDs, and in solid state lighting sources. Therefore the research and the development of WOLED has the special significance.
This paper revolved the fabrication and performance enhancement of WOLEDs and we have done the following work:
Firstly, by employing a polymer PVK as host material doped with fluorescent N-BDAVBi and phosphoresecent Ir(piq)2(acac)and Ir(ppy)_3 , the WOLED with a single light-emitting layer was fabricated successfully. Ir(ppy)_3 was used as a sensitizer. Its brightness reaches 4464cd/m~2 . CIE coordinates is (0.33, 0.38) .The devices show a maximum external efficiency of 0.92%which is higher than the device without Ir(ppy)_3.Then we made another type of single layer WOLED by using PVK: Rubrene:Ir(piq)_2(acac) :N-BDAVBi as light-emitting layer. The CIE coordinate of the device could be well controlled by Rubrene .
Secondly, by using a phosphorescent dye Ir(piq)_2(acac) as a red emitter and TBPe as blue emitter, We fabricated a double light-emitting layers WOLED . Its structure is ITO/NPB/NPB:Ir(piq)_2(acac)/CBP /CBP:TBPe/BCP/ALq/Mg:Ag. On one hand, the introduction of red phosphorescent enhance the efficiency, on the other hand, the blue fluorescent dye employed as blue emitting dye avoided the flaw of the short lifetime for blue phosphorescen and double doping layer devices have simple facture process because of their high doping concentration comparing with single doping layer .By adjusting the proportion and thickness of the dopants,We can get admirable white light. The devices show a maximum external efficiency of 1.24% with the CIE coordinates is (0.33, 0.30) at 8 V. The brightness reaches 7500 cd/m~2 at 15V.
Lastly,In order to improve the performance of double light-emitting device, we employ a high efficiency fluorescent dye N-BDAVBi instead of TBPe and LiF/Al is used as the cathode to enhance electrons injection.The bright and steady light emitting has been obtained.This OLED presents a maximum luminance of 25350cd/m~2 with CIE coordinates of (0.35, 0.35) at 22V and a maximum external quantum efficiency of 6.78% at 8.6V. The CIE coordinates vary slightly as the applied voltage changes from 6V to 22V.
引文
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