Efficient Near‐Infrared Electroluminescence at 840 nm with “Metal‐Free” Small‐Molecule:Polymer Blends

Abstract

The development of efficient and biocompatible organic near-infrared emitters is attractive for many applications, spanning from photodynamic therapy [1] to light fidelity (Li-Fi) all-optical networking systems. [2][3][4] In particular, the range 700-1000 nm is interesting for medical applications, given the semitransparency of biological tissue in this spectral interval, [5] and we will specifically refer to this range as near-infrared (NIR) in the following text. Compared to conventional inorganic materials, organic NIR emitters are interesting also for their mechanical conformability, which makes them appealing for the integration in flexible and stretchable devices. [6] Furthermore, the metal-free organic light-emitting materials can be a cheap and biocompatible alternative to inorganic ones for application in wearable, implantable, or in vivo medical applications, such as for sensing of body temperature, heart and respiration rates, blood pressure, glucose level, and oxygenation. [7] In the search for ever-higher efficiencies, several classes of materials have been investigated, such as perovskite-structured methylammonium lead halides, [8][9][10] quantum dots, [11] and organometallic phosphorescent complexes. [12][13][14][15][16][17][18][19] However, although such hybrid materials afford substantial electroluminescence (EL) external quantum efficiency (EQE) in the NIR, in some cases exceeding 10% [8,10] or even 20% or so, [13] their use of heavy, toxic, and/or costly metals is not ideal for manufacturing, sustainability, environmental impact, and, in perspective, biocompatibility. Furthermore, in such hybrid systems, and in general in materials that leverage triplet excitons to boost the EQE, [20,21] exciton recombination dynamics typically fall in the hundreds of nanoseconds or even in the microsecond (or longer) range, which intrinsically limits the bandwidth when integrated in devices for telecommunications. For Li-Fi applications, [2][3][4] fluorescent molecular and polymeric materials are preferred, given that the typical fluorescence lifetime of these materials is of the order of few nanoseconds or less, thereby ideally allowing data transmission rates up to the Gb s −1 regime.In the last decade, scientists have attempted different strategies to develop heavy-metal-free NIR fluorescent organic light-emitting diodes (OLEDs), with chemical design essentially revolving around the careful combination of donor and acceptor groups to both tune the spectral range (up to 1000 nm) and maximize the EQE. [22][23][24][25][26][27][28][29][30][31][32][33] Very recently, we have, for Due to the so-called energy-gap law and aggregation quenching, the efficiency of organic light-emitting diodes (OLEDs) emitting above 800 nm is significantly lower than that of visible ones. Successful exploitation of triplet emission in phosphorescent materials containing heavy metals has been reported, with OLEDs achieving remarkable external quantum efficiencies (EQEs) up to 3.8% (peak wavelength > 800 nm). For OLEDs incorporating f...

Visible light communication with efficient far-red/near-infrared polymer light-emitting diodes

“…Narrow-gap hybrid organic-inorganic materials and organometallic phosphorescent complexes 26,29,30 , even those characterised by external quantum efficiencies (EQEs) exceeding 10%, are thus less appealing. Interestingly, EQEs in the 1-10% range have also been reported for devices incorporating heavy-metal-free (purely organic) NIR fluorescent dyes 26,[31][32][33] . However, the most efficient of these approaches leverage, to a significant extent, triplet-tosinglet conversion (so-called triplet-triplet annihilation (TTA) or reverse inter-system crossing (rISC)) to obtain high efficiency, with a concomitant intrinsic limitation of the bandwidth even when the problems of the RC time constant can be overcome by reducing the device area 13 .…”

“…However, the most efficient of these approaches leverage, to a significant extent, triplet-tosinglet conversion (so-called triplet-triplet annihilation (TTA) or reverse inter-system crossing (rISC)) to obtain high efficiency, with a concomitant intrinsic limitation of the bandwidth even when the problems of the RC time constant can be overcome by reducing the device area 13 . The maximum EQEs for NIR-emitting devices in which triplet leveraging plays a minor or no role have been limited to 1.2% 32,33 .…”

Dopant‐Free, Donor–Acceptor‐Type Polymeric Hole‐Transporting Materials for the Perovskite Solar Cells with Power Conversion Efficiencies over 20%

“…Fused-ring ladder-type units such as indacenodithiophene (IDT) [37][38][39][40][41] and indacenodithieno [3,2-b]thiophene (IDTT) [38,[41][42][43][44][45][46][47] are classic building blocks of D-A polymers. The coplanar backbones of such polymers enhance both the interchain interactions and hole mobility.…”

Combining Benzotriazole and Benzodithiophene Host Units in Host–Guest Polymers for Efficient and Stable Near‐Infrared Emission from Light‐Emitting Electrochemical Cells

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growing interest for applications in, for example, bioimaging, [1][2][3][4][5] telecommunication, [6][7][8][9][10][11][12] and as chemical sensors, [13][14][15][16][17] due to important advantages such as light weight, flexibility, areal emission, and low power consumption. [18][19][20][21][22] Accordingly, there is currently an intense development of NIR-emitting organic semiconductors, including lanthanide complexes, [23,24] organic small molecules (SMs), [25,26] conjugated polymers, [27][28][29][30] and transition-metal complexes, [11,31] which are implemented in NIR-emissive devices, primarily organic light-emitting diodes (OLEDs). However, a general drawback with efficient OLEDs is that they depend upon a sophisticated multilayer active-material structure and a low-work-function cathode.Compared with conventional OLEDs, the light-emitting electrochemical cell (LEC) exhibits several important advantages.

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