Solution-processed bipolar small molecular host materials for single-layer blue phosphorescent organic light-emitting diodes
作者:Yi-Ting Lee、Yung-Ting Chang、Meng-Ting Lee、Po-Hsuan Chiang、Chin-Ti Chen、Chao-Tsen Chen
DOI:10.1039/c3tc31641f
日期:——
Three new solution processable small molecular host materials based on the bis-[3,5-di(9H-carbazol-9-yl)phenyl] structural moiety have been developed for blue phosphorescent (FIrpic dopant) organic light-emitting diodes. All three host materials have been characterized as having high glass transition temperatures (Tgs), 155–175 °C, indicative of good morphological stability of their amorphous thin films prepared from the solution process. Whereas N,N-bis-[3,5-di(9H-carbazol-9-yl)phenyl]methylamine (CzPAMe) has the highest solid state triplet energy gap (ET) of 2.73 eV, tetrakis-[3,3′,5,5′-(9H-carbazol-9-yl)]triphenylphosphine oxide (CzPPO) and N,N-bis-[3,5-di(9H-carbazol-9-yl)phenyl]pyrimidin-2-amine (CzPAPm) are two host materials which are potentially bipolar for charge transport due to the electron deficient units of phenylphosphine oxide and pyrimidine, respectively. Due to the insufficient ET (2.56 eV) of CzPAPm, CzPPO or CzPAMe devices are significantly better than CzPAPm devices with or without a 1,3-bis[(4-tert-butylphenyl)-1,3,4-oxadiazolyl]phenylene (OXD-7) co-host. Particularly, having no OXD-7 co-host and no vacuum thermal-deposited extra electron transporting layer, single-layer devices of CzPPO surpass CzPAMe devices and reach current efficiencies as high as 9.32 cd A−1 (or power efficiency of 4.97 lm W−1), one of the highest efficiencies among small molecular devices with the same fabrication process and same device configuration.
基于双[3,5-二(9H-咔唑-9-基)苯基]结构分子,为蓝色磷光(FIrpic 掺杂)有机发光二极管开发了三种新型可溶液加工的小分子主材料。这三种主材料都具有较高的玻璃化转变温度(Tgs)(155-175 °C),表明溶液法制备的无定形薄膜具有良好的形态稳定性。N,N-双[3,5-二(9H-咔唑-9-基)苯基]甲胺(CzPAMe)的固态三重能隙(ET)最高,为 2.73 eV,四-[3,3′,5,5′-(9H-咔唑-9-基)]三苯基氧化膦(CzPPO)和 N,N-双-[3、5-二(9H-咔唑-9-基)苯基]嘧啶-2-胺(CzPAPm)是两种宿主材料,它们分别由于苯基氧化膦和嘧啶的缺电子单元而具有潜在的电荷传输双极性。由于 CzPAPm 的 ET(2.56 eV)不足,CzPPO 或 CzPAMe 器件明显优于含有或不含 1,3-双[(4-叔丁基苯基)-1,3,4-恶二唑基]亚苯基(OXD-7)共宿主的 CzPAPm 器件。特别是在没有 OXD-7 共基和真空热沉积额外电子传输层的情况下,CzPPO 的单层器件超过了 CzPAMe 器件,电流效率高达 9.32 cd A-1(或功率效率为 4.97 lm W-1),是具有相同制造工艺和相同器件配置的小分子器件中效率最高的器件之一。