Abstract
In organic light-emitting diodes (OLEDs), horizontal orientation of the emissive transition dipole moment (TDM) can improve light outcoupling efficiency by up to 50% relative to random orientation. Therefore, there have been extensive efforts to identify drivers of horizontal orientation. The aspect ratio of the emitter molecule and the glass-transition temperature (Tg ) of the films are currently regarded as particularly important. However, there remains a paucity of systematic studies that establish the extent to which these and other parameters control orientation in the wide range of emitter systems relevant for state-of-the-art OLEDs. Here, recent work on molecular orientation of fluorescent and thermally activated delayed fluorescent emitters in vacuum-processed OLEDs is reviewed. Additionally, to identify parameters linked to TDM orientation, a meta-analysis of 203 published emitter systems is conducted and combined with density-functional theory calculations. Molecular weight (MW) and linearity are identified as key parameters in neat systems. In host-guest systems with low-MW emitters, orientation is mostly influenced by the host Tg , whereas the length and MW of the emitter become more relevant for systems involving higher-MW emitters. To close, a perspective of where the field must advance to establish a comprehensive model of molecular orientation is given.
Highlights
Organic light-emitting diodes (OLEDs) are electroluminescent solid-state light sources in which the active light-emitting materials consist of organic or organometallic molecules, dendrimers, or polymers are currently regarded as important
In the more than three decades since the first OLED was reported,[1] progress has been dramatic and these devices are finding numerous commercial applications: a substantial fraction of modern smartphone displays are based on OLEDs, large-area OLED TVs are rapidly gaining in popularity, and OLED-based luminaires may well provide
We provide an overview of the state of the art in emitter orientation studies for fluorescent and thermally activated delayed fluorescence (TADF) OLEDs, noting how the key parameters have been identified so far, and reviewing new, promising strategies for achieving horizontally oriented emitters
Summary
Organic light-emitting diodes (OLEDs) are electroluminescent solid-state light sources in which the active light-emitting materials consist of organic or organometallic molecules, dendrimers, or polymers are currently regarded as important. Paucity of systematic studies that establish the extent to which these and other parameters control orientation in the wide range of emitter systems relevant for state-of-the-art OLEDs. Here, recent work on molecular orientation of fluorescent and thermally activated delayed fluorescent emitters in. In host–guest systems with low-MW emitters, orientation is mostly influenced by the host Tg, whereas the length and MW of the emitter become ibility and an amorphous structure. These properties make them well suited for producing optoelectronic devices with an attractive combination of properties, such as mechanical flexibility, versatile more relevant for systems involving higher-MW emitters.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
