Effects of Charge Dynamics in the Emission Layer on the Operational Lifetimes of Blue Phosphorescent Organic Light‐Emitting Diodes. (31st January 2022)

• Record Type: Journal Article
• Authors: Yang, Kwangmo; Nam, Sungho; Kim, Joonghyuk; Kwon, Eun Suk; Jung, Yongsik; Choi, Hyeonho; Kim, Ji Whan; Lee, Jaesang
• Is Part Of: Advanced functional materials. Volume 32:Number 19(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-01-31
• Subjects: defects -- degradation -- dopant carriers -- phosphorescent organic light‐emitting diodes -- triplet‐polaron annihilation; Materials -- Periodicals; Chemical vapor deposition -- Periodicals; 620.11
• DOI: 10.1002/adfm.202108595
• Languages: English
• ISSNs: 1616-301X

Abstract

Abstract: Despite more than 20 years of research, the root cause of the impractically short lifetimes of blue phosphorescent organic light‐emitting diodes (PHOLEDs) has remained unclear. To overcome this, the authors investigate how the electrical properties of the emission layer (EML) of blue PHOLEDs affect degradation of the devices. It is found that a large density of dopant carriers is the dominant factor triggering triplet‐polaron annihilation (TPA), which is a major defect‐generation and hence lifetime‐reduction mechanism. In order to reduce the generation of the TPA‐induced defects to ensure long device lifetimes, the dopant carrier density should be minimized by suppressing the spontaneous charge transfer from the host to the dopant initially and by supplying sufficient charges with opposite polarity into the EML. However, there exists another critical factor that offsets the low overall density of defects against device lifetimes—that is, the non‐uniform distribution of defects leading to intense exciton quenching. These two degradation factors are predetermined, and hence can be controlled, by the charge mobilities of the PHOLED EML. Given these considerations, it is demonstrated that the long‐lifetime blue PHOLEDs can be realized. Abstract : A high density of dopant carriers is found to be the primary cause of the degradation of blue phosphorescent organic light‐emitting diodes (PHOLEDs) by inducing defect‐generation process. Accordingly, the authors demonstrate that the lifetimes of blue PHOLEDs can be enhanced by minimizing the dopant carrier density and by alleviating the detrimental interactions between charges, excitons and defects.