Nonlocal effect of excited carriers on the bond strength of carbazole-based OLED host materials

Abstract

Despite the decades of development and successful implementations of organic light-emitting diodes (OLEDs) in various devices, the poor reliability mainly incurred by chemical degradations has remained a crucial issue. The overall mechanism of degradation has been outlined as an effect of excited carriers, and its microscopic details have yet to be understood. Here, using occupation-constrained density functional theory calculations, we investigate the role of excited carriers on the stability of OLED host materials. Unlike the electronic ground state, in which the chemical stability is mainly determined by the local atomic structure, the stability in the excited state is largely affected by the entire molecular structure, resulting in a nonlocal effect in the chemical degradation. Our results suggest the importance of this nonlocal effect in the excited state, represented by the excited carrier energy and potential energy landscape, to improve the reliability of the OLED device.