Chemical transformations of common hole transport materials in operating OLED devices

Denis Kondakov

doi:10.1117/12.796824

2 September 2008 Chemical transformations of common hole transport materials in operating OLED devices

Denis Kondakov

Author Affiliations +

Proceedings Volume 7051, Organic Light Emitting Materials and Devices XII; 70510I (2008) https://doi.org/10.1117/12.796824
Event: Photonic Devices + Applications, 2008, San Diego, California, United States

Abstract

Despite active scientific research and substantial business interest, the nature of the operational degradation of OLEDs remains only partly understood. From the perspective of device physics, there are numerous studies indicating that operational degradation, i.e., monotonic loss of luminance efficiency and increase of drive voltage, is caused primarily by the accumulation of traps-nonradiative recombination centers and luminescence quenchers in the vicinity of the recombination zone. However, chemistries underlying the formation of those species remain elusive. In this work, we focused on two representative hole transport materials, NPB and TAPC, to study their chemical transformations in operating OLED devices. We found that the presence of these hole transport materials in several representative fluorescent and phosphorescent devices may result in the formation of new chemical materials, corresponding to homolytic dissociation of weak C-N bonds of NPB, and C-N/C-C bonds of TAPC. Qualitatively similar to luminance efficiency loss in operating devices, the accumulation of the degradation products is monotonic and nonlinear. Using bilayer hole transport layers, we established that the chemistries of NPB and TAPC are strongly confined to the immediate vicinity of the main recombination interfaces and are likely to be initiated by singlet excited states of these arylamines. It is concluded that the differences in singlet excited state energies and bond dissociation energies are responsible for dramatic differences in the degradation rates of OLED devices using NPB- and TAPC-based hole transport layers.

Citation Download Citation

Denis Kondakov "Chemical transformations of common hole transport materials in operating OLED devices", Proc. SPIE 7051, Organic Light Emitting Materials and Devices XII, 70510I (2 September 2008); https://doi.org/10.1117/12.796824

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