Highly Efficient and Spectrally Narrow Near‐Infrared Fluorescent OLEDs Using a TADF‐Sensitized Cyanine Dye

Abstract

Through various triplet‐harvesting approaches, fluorescent organic light‐emitting diodes (OLEDs) that emit in the visible spectrum can now be fabricated with efficiencies rivaling those of their phosphorescent counterparts. However, achieving high efficiencies in the near‐infrared (NIR) is considerably more challenging. This is in part due to the low quantum yield of most fluorescent NIR emitters and inefficient triplet exciton harvesting in such devices. Here, fluorescent NIR OLEDs with an external quantum efficiency of 5.4% and a peak emission wavelength of 790 nm are demonstrated. The OLEDs are fabricated by combining a deep‐red host that undergoes thermally assisted delayed fluorescence with a near‐infrared cyanine dye that emits with high efficiency. The devices show nearly pure NIR emission with a NIR cut‐on wavelength of 749 nm and >90% emitted power at wavelengths above 750 nm. It is also shown that the host polarity strongly affects the device performance.

Near‐Infrared Electroluminescence beyond 800 nm with High Efficiency and Radiance from Anthracene Cored Emitters

“…Remarkably,both absorption (Supporting Information, Figure S11) and PL spectra from doped to neat films suggest that the band gaps of DCPA-TPAand DCPA-BBPAare further decreased in neat films by increasing surrounding polarities.B esides,t he lifetimes of DCPA-TPAa nd DCPA-BBPAi na ggregate states (Supporting Information, Figure S12, both doped and non-doped) are changed to multi-order fitting type,w hich indicates the external channel for emission were formed due to the intermolecular interactions in aggregation states.And similar phenomena were also reported for red and NIR emitters. [18,21] TheP LQYs of neat films for DCPA-TPAa nd DCPA-BBPA are 8% and 3%,r espectively,w hich is comparable to reported NIR fluorescence and phosphorescence materials with similar PL spectra. [2d, 22] Whereas,t he PLQYs of doped films in CBP (Supporting Information, Table S3) are largely increased due to the lessened intermolecular interactions.The PLQYs of 10/20/30 wt %D CPA-TPAa nd DCPA-BBPAi n CBP are 49 %/41 %/33 %a nd 38 %/25 %/16 %, respectively.…”

Harvesting triplet excitons for near-infrared electroluminescence via thermally activated delayed fluorescence channel

“…The optimized sensitized device exhibited an EQE as high as 2.65% with a peak at 730 nm. In 2019, Brodeur et al reported a TADF-sensitized NIR device, which exhibited a relative pure NIR emission with an NIR cut-on wavelength of 749 nm and more than 90% spectra fall into the region above 750 nm (Brodeur et al, 2019). In 2020, Shahalizad et al reported a hyperfluorescent device ( Figure 5), in which the NIR TADF emitter named TPAM-BF2 serves as a sensitizer for the pyrrolopyrrole cyanine dyes corded as BPPC-Ph (Shahalizad et al, 2020).…”

“…In 2019, Brodeur et al. reported a TADF-sensitized NIR device, which exhibited a relative pure NIR emission with an NIR cut-on wavelength of 749 nm and more than 90% spectra fall into the region above 750 nm ( Brodeur et al., 2019 ). In 2020, Shahalizad et al.…”

“…(2017) 49.5/50/0.5 – 3.3 (at 10 mA cm -2 ) 780 1/−/− DMAC-PN/TPANSeD 98/2 – 2.36 722 -/7830/- Xue et al. (2017) 96/4 – 2.65 730 -/10,569/- 94/6 – 2.11 731 -/24,624/- B3PYMPM/TPA-DCPP/DCPP 79.2/20/0.8 22 5.4 790 −/−/- Brodeur et al. (2019) TPBi/TPA-DCPP/DCPP 79.2/20/0.8 10 2.2 790 −/−/- CBP/TPAF-BF2/BPPC-Ph 79.5/20/0.5 15.8 3.5 840.7 −/−/- Shahalizad et al.…”

Highly Efficient Near‐Infrared Electrofluorescence from a Thermally Activated Delayed Fluorescence Molecule

“…Among other light-sources, organic LEDs (OLEDs) [5] are considered to be a potential alternative because of their intrinsic advantages such as ultra-flexibility, ultra-lightweight, high uniformity of light emission, and the possibility for low-cost fabrication. Indeed, many organic [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] and organometallic [22][23][24][25] com-pounds have been developed and applied as emitters for NIR-OLEDs. However, NIR-OLEDs suffer from low external EL quantum efficiency (EQE) caused by unbalanced charge trapping, [25] aggregation-caused quenching, [15] and accelerated nonradiative deactivation of the excitons through a vibration coupling with a ground state, that is, energy-gap law.…”