Ultrahigh Polarization of Emitted Light by Quenched Emissive Material

Abstract

AbstractThe emission of highly polarized light by organic light‐emitting diodes (OLEDs) is crucial for various applications; however, achieving such emission requires the use of polarizers, which reduce the device efficiency and durability. In this study, ultrahigh‐polarized light with a polarization ratio (PR) of 407:1 is achieved via the rapid thermal quenching (RTQ) of OLEDs. Poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) films, molybdenum disulfide (MoS2) nanosheets, and tungsten disulfide (WS2) nanosheets are applied as hole transport layers and surface‐alignment layers through surface treatment, including rubbing and/or ion‐beam exposure to align the molecules of the emissive materials, namely, {poly(9,9‐dioctylfluorene‐alt‐benzothiadiazole) (F8BT). Quenching is performed at 240 °C, at which F8BT has a nematic liquid crystal (NLC) phase with high molecular ordering. Upon quenching, the high molecular ordering of the NLC‐phased emissive layer instantaneously froze via RTQ, leading to the emission of highly polarized light. Consequently, the PEDOT:PSS‐, MoS2‐, and WS2‐based OLEDs exhibit ultrahigh PRs of 407:1, 349:1, and 328:1, respectively, for photoluminescence at a 540 nm peak wavelength. In contrast, for electroluminescence, the PEDOT:PSS‐based OLED exhibits a high PR of 395:1. This result is the best reported to date and is comparable to the PRs generated by polarizers, indicating that quenching can be utilized for the development of ultrahigh‐polarized light‐emitting devices.