基于MADN空穴传输层的双层结构高效率黄绿光OLED及其阻抗谱分析

Highly Efficient Bilayer-Structure Yellow-Green OLED with MADN Hole-Transport Layer and the Impedance Spectroscopy Analysis

以MADN为空穴传输层,主-客掺杂体系[Alq3∶0.7 Wt%rubrene]为发光兼电子传输层,构建了双层结构的高效率黄绿光OLED器件。该器件的黄绿光由主发光体Alq3通过不完全能量转移到客发光体rubrene实现,电致发光峰值位于560nm,1931CIE色坐标为(0.46,0.52),最大发光效率达到了7.63cd·A-1,比相应的NPB做空穴传输层的双层结构器件提高了30%。通过构建以MADN或NPB为空穴传输层的空穴单载流子器件并进行阻抗谱分析,结果表明MADN可以作为一种非常有效的空穴传输层,其空穴迁移性略低于NPB,这恰好弥补了OLED器件中空穴迁移比电子迁移快这一缺陷,为改善OLED发光层中载流子的平衡性创造了条件,从而提高了器件的发光效率。此外,MADN做空穴传输层的双层结构OLED的发光效率与传统三层结构器件(MADN和Alq3分别作为空穴传输层和电子传输层)基本相当,表明了这种双层结构器件在简化器件结构的同时并不以牺牲发光效率为代价,发光层[Alq3∶0.7 Wt%rubrene]兼具有优良的电子传输性能。

Highly efficient bilayer-structure yellow-green organic light-emitting device （OLED） has been demonstrated based on MADN as hole-transport layer （HTL） and host-guest coped system of [-Alq3 ： 0.7 Wt%rubrene＇] as emitting and electron-transport layer. The device gives yellow-green emission through incomplete energy transfer from the host of Alqa to the guest of rubrene. An electroluminescent peak of 560 nm, 1931 CIE color coordinates of （0. 46, 0.52） and a maximum current efficiency of 7.63 cd · A^-1 （which has been enhanced by 30% in comparison with the counterpart having conventional NPB HTL） are observed. The hole-transporting characteristics of MADN and NPB have been systematically investigated by constructing hole-only devices and employing impedance spectroscopy analysis. Our results indicate that MADN can be served as an effective hole-transport material and its hole-transporting ability is slightly inferior to NPB. This overcomes the shortcoming of hole transporting more quickly than electron in OLED and improves carrier balance in the emitting layer. Consequently, the device current efficiency is promoted. In addition, the current efficiency of bilayer-strueture OLED with MADN as HTL is comparable to that of conventinol trilayer-structure device with MADN as HTL and Alq3 as electron-transport layer. This indicates that the simplified bi- layer-structure device can be achieved without sacrificing current efficiency. The emitting layer of /-Alq3 ： 0.7 Wt% rubrene3 possesses superior elecron-transporting ability.