High-efficiency organic light-emitting diodes with exciplex hosts

Author(s): Qiang Wang ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Qi-Sheng Tian ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Yuan-Lan Zhang ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Xun Tang ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Liang-Sheng Liao ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵

Publication date (Electronic): 2019

Journal: Journal of Materials Chemistry C

Publisher: Royal Society of Chemistry (RSC)

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Abstract

Exciplex forming co-hosts have been applied to fabricate high-efficiency organic light-emitting diodes (OLEDs) due to the merits of bipolarity, 100% exciton harvesting, preferred dipole alignment, and sensitizing effects. We review the discovery and development of the exciplex mechanism framework, from its discovery to successful application as hosts for phosphorescent OLEDs (PhOLEDs), thermally activated delayed fluorescence (TADF) OLEDs, and hyperfluorescent OLEDs, as well as in white OLEDs (WOLEDs). Exciplex forming co-hosts utilize the TADF effect to guarantee high exciton utilization efficiency. The charge-injection-free energy level configuration decreases the driving voltages and brings about improved power efficiency. The increased transitional dipole moment of emitters in exciplex forming co-hosts adds outcoupling efficiency to beat the efficiency limit. Exciplexes with the TADF effect also show sensitizing effects, making high-efficiency fluorescent OLEDs possible. This review introduces the progressive achievements of exciplex forming co-hosts, aimed at forming a summary of the present research on exciplex based OLEDs, and hopefully helping researchers grasp the future developing trend of exciplex forming co-hosts.

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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.