Heavily Doped, Charge-Balanced Fluorescent Organic Light-Emitting Diodes from Direct Charge Trapping of Dopants in Emission Layer

详细信息    查看全文

• 作者：Sang Ho Rhee ; Sung Hyun Kim ; Hwang Sik Kim ; Jun Young Shin ; Jeeban Bastola ; Seung Yoon Ryu
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2015
• 出版时间：August 5, 2015
• 年：2015
• 卷：7
• 期：30
• 页码：16750-16759
• 全文大小：565K
• ISSN：1944-8252

文摘

We studied the effect of direct charge trapping at different doping concentrations on the device performance in tris(8-hydroxyquinoline) aluminum (Alq₃):10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-(1)-benzopyropyrano(6,7鈥?-i,j)quinolizin-11-one (C545T) as a host鈥揹opant system of a fluorescent organic light-emitting diode. With increasing C545T doping concentration, trap sites could lead to the promotion of hole injection and the suppression of electron injection due to the electron-transport character of Alq₃ host for each carriers, as confirmed by hole- and electron-only devices. Direct charge injection of hole carriers from the hole transport layer into C545T dopants and the charge trapping of electron carriers are the dominant processes to improve the charge balance and the corresponding efficiency. The shift of the electroluminescence (EL) spectra from 519 nm to 530 nm was confirmed the exciton formation route from F枚rster energy transfer of host鈥揹opant system to direct charge trapping of dopant-only emitting systems. Variation in the doping concentration dictates the role of the dopant in the fluorescent host鈥揹opant system. Even though concentration quenching in fluorescent dopants is unavoidable, relatively heavy doping is necessary to improve the charge balance and efficiency and to investigate the relationship between direct charge trapping and device performance. Heavy doping at a doping ratio of 6% also generates heavy exciton quenching and excimer exciton, because of the excitons being close enough and dipole鈥揹ipole interactions. The optimum device performance was achieved with a 4%-doped device, retaining the high efficiency of 12.5 cd/A from 100 cd/m² up to 15鈥?00 cd/m².