A set of novel lithium Schiff base cluster compounds has been synthesised and characterised for the first time and tested as electron injectors in OLED devices. Their electrical, electronic, thermal and optical properties have been investigated and compared with the industry standards LiF and lithium quinolinolate (LiQ). Amongst the compounds tested, lithium 2-((o-tolylimino)methyl) phenolate was found to enhance the efficiency of OLEDs by 69% compared to LiF and 15% compared to LiQ. The same electron injector was found to extend the lifetimes of OLEDs by six-fold compared to LiF and 4.3-fold compared to LiQ respectively. The crystal structure of the parent compound, lithium 2-((phenylamino)methyl)phenolate reveals that the compound is tetrameric in contrast to hexameric LiQ. Substituting the methyl group with fluorine causes a remarkable depression of the HOMO and LUMO levels by up to 1.2 eV. Analysis of current density vs. voltage characteristics of single-layer devices for Li–Al/electron injector/Li–Al and Al/electron injector/Al reveals that both sets of devices are operating as electron-only devices indicating that the formation of free lithium is the cause of enhanced electron injection, but either the energetic aluminium atoms (as proposed previously by other workers) or energetic lithium complexes on an aluminium surface (as we have demonstrated in this paper) are all that is required for efficient electron injection.
首次合成并表征了一组新型的
锂席夫碱簇合物,并将其作为电子注入剂在OLED器件中进行了测试。研究了这些化合物的电学、电子学、热学和光学性质,并与工业标准物
LiF和
锂喹啉酸盐(LiQ)进行了比较。在测试的化合物中,
锂2-((邻
甲苯基亚
氨基)甲基)
苯酚盐被发现能使OLED的效率比
LiF提高69%,比LiQ提高15%。同样的电子注入剂被发现能使OLED的寿命比
LiF延长六倍,比LiQ延长4.3倍。母体化合物
锂2-((
苯胺基)甲基)
苯酚盐的晶体结构表明,该化合物是四聚体,与六聚体的LiQ不同。用
氟原子替换甲基会导致HOMO和LUMO能级显著降低,高达1.2 eV。对Li–Al/电子注入剂/Li–Al和Al/电子注入剂/Al的单层器件的电流密度与电压特性的分析表明,两组器件都在作为纯电子器件运行,表明自由
锂的形成是提高电子注入的原因,但无论是能量化的铝原子(如其他工作者之前所提出的)还是铝表面上的能量化的
锂复合物(如我们在本文中所展示的),都是实现高效电子注入所需的全部条件。