Efficient Triplet–Triplet Annihilation Upconversion in an Electroluminescence Device with a Fluorescent Sensitizer and a Triplet‐Diffusion Singlet‐Blocking Layer

Abstract

energy transfer (TET) populates the triplet state of the TTA emitter. When two triplet excitons encounter each other, the TTA process puts the emitter into its singlet excited state to emit fluorescence. One criterion for the sensitizer is efficient ISC to convert the singlet to the triplet, and sensitizers like phosphors, thermally activated delay fluorescence emitters, inorganic quantum dots, and perovskites have been used. [5][6][7] Charge transfer states between electron donor and acceptor materials can also act as sensitizers, resulting in efficient sub-bandgap emission (i.e., the driving voltage is ≈1/2 of the emitted photon energy) for organic light-emitting diode (OLED) applications. [8] For electrical excitation, 75% of the electron-hole pairs recombine as triplets without any ISC. By harnessing these triplet excitons to generate luminescence, TTAUC provides a path to higher efficiency devices.In this Communication, we show that a new device architecture can significantly improve TTAUC blue emission efficiencies, which is one of the important issues for OLED development. [9] The basic idea is to separate the triplet sensitization and upconversion layers while still allowing triplet energy migration. To demonstrate this concept, tris-(8-hydroxyquinoline)aluminum (Alq 3 ) was used as the sensitizer. This molecule has been used as an electron-transporting layer (ETL) and emitting layer material in one of the first OLED Solid-state triplet-triplet annihilation upconversion (TTAUC) blue emission in an electroluminescence device (i.e., an organic light-emitting diode (OLED)) is demonstrated. A conventional green fluorophore, tris-(8-hydroxyquinoline)aluminum (Alq 3 ), is employed as the sensitizer that generates 75% triplet under electrical pumping for the blue triplet-triplet annihilation emitter, 9,10-bis(2′-naphthyl) anthracene (ADN), with the heterojunction bilayer structure. The operation lifetime is elongated both for ADN blue (4.1x) and Alq 3 green (34.8%) emission due to efficient use of excitons and separation of recombination and emission zone. To reduce the singlet quenching (SQ) of blue TTAUC signal by the Alq 3 sensitizer with lower bandgap, 1-(2,5-dimethyl-4-(1-pyrenyl)phenyl)pyrene (DMPPP) is inserted between the Alq 3 and ADN as a triplet-diffusion-and-singlet-blocking layer. DMPPP exhibits triplet energy close to Alq 3 and higher than ADN, as well as higher singlet energy than both Alq 3 and ADN. It allows triplet diffusion from Alq 3 to ADN, but blocks the SQ of the blue TTAUC signal by Alq 3 . 86.1% intrinsic efficiency of TTAUC is demonstrated in this trilayer (Alq 3 /DMPPP/ADN) OLED. Organic Light-Emitting DiodesThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.

Strategies for High‐Performance Solid‐State Triplet–Triplet‐Annihilation‐Based Photon Upconversion

“…Therefore, we insert 1-[2,5,-dimethyl-4-(1-pyrenyl)phenyl]pyrene (DMPPP), which has higher singlet energy than MADN and BDAVBi, between PtOEP and MADN:BDAVBi to reduce direct Förster resonance energy transfer (FRET) from the annihilator to the sensitizer. [24] To ensure that DMPPP does not block triplet transfer This article is protected by copyright. All rights reserved.…”

Precise Regulation of Distance between Associated Pyrene Units and Control of Emission Energy and Kinetics in Solid State

“…In addition, combined with the triplet-triplet annihilation (TTA) process, there are also long-lived excited states. [42][43][44][45] Actually, the control of emission energy and lifetime is a distinct advantage for designing materials with special optoelectronic properties in the solid state. [46][47][48] However, it is still unclear what the influence of distances between π-conjugated planes in pyrene excimers is on their photophysical properties in solid state, let alone the qualitative and quantitative analysis of their π-π interactions in the solid state.…”

Realization of high-efficiency fluorescent organic light-emitting diodes with low driving voltage

“…Figure 1 presents a schematic diagram of the energy transfer and up-conversion emission mechanism in CT-assisted OLEDs with EL at sub-bandgap voltages. Although these CT-assisted devices can have EL at sub-bandgap voltages corresponding to the energy of the CT state, they are inherently inefficient due to the energy down-flow (quenching) from the emitter back to the CT-state, and therefore the EL quantum efficiency is typically low, and high efficiency sub-bandgap OLEDs remain out of reach 15–19 . In this work, we demonstrate that organic molecules with a large singlet-triplet splitting which also exhibit P-type delayed fluorescence can form triplet excitons via direct charge injection, and result in efficient EL at sub-bandgap voltages close to their triplet energy without the presence of any exciplex states.…”