High performance OLEDs using deep red (DR) and near-infrared (NIR) TADF emitters

Descripción del proyecto

Nueva generación de OLED de alta eficiencia basados en emisores de radiación roja profunda e infrarroja cercana

La fluorescencia retardada activada térmicamente (TADF, por sus siglas en inglés) es un mecanismo que permite mejorar la eficiencia de los diodos orgánicos electroluminiscentes (OLED, por sus siglas en inglés). Los dispositivos que utilizan este mecanismo se conocen como OLED de tercera generación y tienen una eficiencia cuántica interna cercana al 100 %. Hasta ahora, se sabe muy poco sobre los materiales basados en la TADF que emiten luz en la frecuencia del rojo profundo o infrarrojo cercano. Dichos materiales podrían emplearse en dispositivos de visión nocturna, sensores y dispositivos de acceso seguro. El proyecto TADFNIR, financiado con fondos europeos, utilizará métodos racionales de síntesis orgánica de materiales para producir emisores de TADF en estas frecuencias. El objetivo del proyecto es resolver tres problemas principales relacionados con los emisores OLED TADF actuales, a saber: la reducción gradual de la eficiencia, su corta vida útil y la baja pureza del color de emisión.

Objetivo

First-generation fluorescent and second-generation phosphorescent organic light-emitting diodes (OLEDs) can achieve maximum internal quantum efficiency (IQE) of 25% and 100%, respectively. Phosphorescent OLEDs with complexes based on iridium and platinum realize 100% IQE due to the heavy atom effect. However, there are limitations, including but not limited to their scarcity and toxicity profile. The third generation OLEDs based on a thermally activated delayed fluorescence (TADF) process can be realized in purely organic materials and produce devices with 100% IQE. So far, there are examples of high-performance blue, green and red TADF OLEDs; however, limited attention has been paid to deep red (DR) and near-infrared (NIR) TADF emitters (650-750 nm). Such DR and NIR emitters find applications in night vision displays, sensors and information-secured displays etc. Current NIR OLEDs are associated with issues related to efficiency roll-off, lifetime and purity of emission color. Most importantly, the materials contain osmium, iridium, or platinum metals and therefore these OLEDs suffer from the same issues as visible light phosphorescent counterparts. This proposal seeks to address the above issues by rational design of purely organic novel DR and NIR TADF emitters. Our design comprises of yet unexplored rigid anthrone-based strong electron acceptor decorated with suitably substituted donor carbazoles. Emission color tunability can be achieved as a function of donor choice and position and varying the strengths of either the donor or acceptor. The rigidity of the molecular components, the strengths of the acceptor/donor, the twisted conformation, and the presence of tertiary butyl groups on the carbazoles altogether will work coherently to furnish good device stability, reduced efficiency roll-off, narrow emission spectra and an improved lifetime of the OLEDs. Overall, this proposal is anticipated to provide a major breakthrough in DR and NIR TADF emitters.