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Phase behaviors of NPB molecule under vacuum

Research paper by Seob Shim, Jin-Tae Kim, Eun-Jin Shin, Nak-Kwan Chung, Ohyun Kwon, Ju-Young Yun

Indexed on: 19 Mar '16Published on: 02 Feb '16Published in: Materials Research Bulletin



Abstract

Commercialization of organic light emitting diodes (OLEDs) with high stability and reproducibility remains challenging. Although many studies have evaluated the intrinsic (electrochemical, photochemical, and thermal degradation of the active layers) and extrinsic (encapsulation and layer adhesion) degradation mechanisms of OLED devices and have attempted to improve device stability, until recently little attention was paid to the phase behavior of the deposition materials used in OLEDs during evaporation. In addition to intrinsic and extrinsic factors, phase behaviors may also affect device efficiency and lifetime as they play key roles in optimizing the evaporation process under high vacuum and subsequently reducing manufacturing costs. In this study, the phase behavior of N,Nʹ-diphenyl-N,Nʹ-bis(1-naphthyl)-1,1ʹ-biphenyl-4,4ʺ-diamine (NPB: C44H32N2), a widely used as hole transporting material in OLEDs, was investigated under vacuum. The resulting phase diagram under vacuum will be useful to understand the nature of thermal evaporation for the NPB molecule for use in OLED manufacture.

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