Thermally activated delayed fluorescence materials for organic light-emitting diodes

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Abstract

Recently, the remarkable advances in thermally activated delayed fluorescence (TADF) materials have attracted much attention due to their 100% exciton utilization efficiency in organic light-emitting diodes (OLEDs). Although the commercialization of TADF materials is at an early stage, they exhibit enormous potential for next-generation OLEDs due to the comparable electroluminescence performance to metal of their phosphorescent complex counterparts, but without the presence of precious metal elements. This review summarizes the different types of TADF small molecules with various photophysical properties and the state-of-the-art molecular design strategies. Furthermore, the device engineering is discussed, and emerging optoelectronic applications, such as organic light-emitting electrochemical cells, organic lasing, and organic scintillators, are introduced. It is anticipated that this review can clarify the design of efficient TADF emitters and point out the direction of future development.

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Highly efficient organic light-emitting diodes from delayed fluorescence.

Hiroki Uoyama, Kenichi Goushi, Katsuyuki Shizu … (2012)

The inherent flexibility afforded by molecular design has accelerated the development of a wide variety of organic semiconductors over the past two decades. In particular, great advances have been made in the development of materials for organic light-emitting diodes (OLEDs), from early devices based on fluorescent molecules to those using phosphorescent molecules. In OLEDs, electrically injected charge carriers recombine to form singlet and triplet excitons in a 1:3 ratio; the use of phosphorescent metal-organic complexes exploits the normally non-radiative triplet excitons and so enhances the overall electroluminescence efficiency. Here we report a class of metal-free organic electroluminescent molecules in which the energy gap between the singlet and triplet excited states is minimized by design, thereby promoting highly efficient spin up-conversion from non-radiative triplet states to radiative singlet states while maintaining high radiative decay rates, of more than 10(6) decays per second. In other words, these molecules harness both singlet and triplet excitons for light emission through fluorescence decay channels, leading to an intrinsic fluorescence efficiency in excess of 90 per cent and a very high external electroluminescence efficiency, of more than 19 per cent, which is comparable to that achieved in high-efficiency phosphorescence-based OLEDs.