Hidden Confinement Induced by Charged Excitons: External Electric Field Adjustment to Achieve Highly Efficient Fluorescence in PLEDs

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• 作者：Renai Chen ; Weikang Chen ; Deyao Jiang ; Sheng Li ; Thomas F. George
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：September 3, 2015
• 年：2015
• 卷：119
• 期：35
• 页码：20312-20318
• 全文大小：404K
• ISSN：1932-7455

文摘

Experiments have shown that intensive charge injections are able to greatly enhance the efficiency of polymer light emitting diodes (PLEDs). Yet, under strong external electric filed/high voltages, there is a certain degree of efficiency roll-off. For this paradox, this article reveals the following underlying mechanism: Under a low electric field, a charged polaron is driven to the potential well created by an exciton, where they fuse together to form a 鈥渃harged exciton鈥? The carrier fusion induces the triplet state to fluoresce, which greatly enhances the performance of the device (ideally, the internal quantum efficiency can exceed 95%). As long as the external field continues to increase and surpasses 4.5 脳 10⁴ V/cm, the above confinement is broken, and the polaron also steps out of the potential well, which leads to a major setback of the overall device efficiency. Then, when the electric field reaches as high as 0.8 MV/cm, the original exciton is dissociated. For achieving highly efficient fluorescent PLEDs, it is seen that the appropriate electric field magnitude ranges from 5 脳 10² to 2 脳 10⁴ V/cm.