Recent Progress in Emerging Near-Infrared Emitting Materials for Light-Emitting Diode Applications

Abstract

In view of the wide applications of near-infrared (NIR) light in night vision, security, medicine, sensors, telecommunications, and military applications, and the scarcity of high-efficiency NIR-emitting materials, development of alternative NIR-emitting materials is urgently required. In this review, we focus on three kinds of emerging NIR-emitting materials used in light-emitting diodes (LEDs), namely organic materials, inorganic quantum dot (QD) materials, and organic–inorganic hybrid perovskite materials; the corresponding devices are organic LEDs, QD LEDs, and perovskite LEDs. The advantages and disadvantages of the three kinds of materials are discussed, some representative works are reviewed, and a brief outlook for these materials is provided.

Bright short-wavelength infrared organic light-emitting devices

“…However, unlike the success in the visible 1 and NIR region [3][4][5]13,15,16 , bright OLEDs in the SWIR range have not been demonstrated so far. The main reason for this could be ascribed to the limitation subject to the energy-gap law [3][4][5] , which predicts an exponentially increased non-radiative decay rate with decreasing energy gap in organic solids, as a result of the increased electron-phonon coupling between the excited and ground states. This limitation indicates, if the energy-gap law is strictly valid, long wavelength emission from organic solids is extremely weak and there is a major bottleneck for extending the emission to longer wavelengths.…”

“…Organic semiconductors with advantageous electronic and optoelectronic properties have enabled demonstration of high-performance organic light-emitting devices (OLEDs) with emission covering the visible, near-ultraviolet and near-infrared parts of the electromagnetic spectrum [1][2][3][4][5] . There has been long-standing demand for the development of electrically driven short-wavelength infrared (SWIR, 1000-2000 nm) 6,7 light sources in view of their broad range of applications, including optical communications [3][4][5] , night-vision surveillance 3,4,6 and remote sensing 8 .…”

“…Organic semiconductors with advantageous electronic and optoelectronic properties have enabled demonstration of high-performance organic light-emitting devices (OLEDs) with emission covering the visible, near-ultraviolet and near-infrared parts of the electromagnetic spectrum [1][2][3][4][5] . There has been long-standing demand for the development of electrically driven short-wavelength infrared (SWIR, 1000-2000 nm) 6,7 light sources in view of their broad range of applications, including optical communications [3][4][5] , night-vision surveillance 3,4,6 and remote sensing 8 . Recent emerging applications in biological imaging [9][10][11] , medical analyses 12 and infrared spectroscopy 9 for health, food and environmental monitoring require the development of bright, biocompatible SWIR emitters, as longer imaging wavelengths promise lower light scattering, deeper tissue penetration depth and superior spatiotemporal resolution [9][10][11] compared to the visible and near infrared (NIR, 700-1000 nm) counterparts.…”

“…Despite such major fundamental hurdle, extensive research efforts have been dedicated to narrowing the energy gap and realizing electroluminescence beyond the visible region, i.e., 700-1000 nm near-infrared emission in organic solids by adopting rational strategies used for visible emitters. These strategies generally involve several key considerations [3][4][5] , such as extending conjugation length, reducing bond length alternation (corresponding to greater π-electron delocalization), introduction of appropriate donor-acceptor charge transfer units and use of triplet 17 or doublet excitons 18 . As a result, nowadays organic emitters available for NIR OLEDs includes mainly organometallic phosphorescent complex 19,20 , organic ionic dyes 21 , conjugated polymers 22 , organic compounds containing donor-acceptor charge transfer chromophores 3,5,18,[23][24][25] , thermally activated delayed fluorescent (TADF) materials 26 and doublet emitters 18 .…”

Red to NIR-emissive anthracene-conjugated PMI dyes with dual functions: singlet-oxygen response and lipid-droplet imaging

“…In recent years, deep red and near-infrared (NIR) emitting materials have captured the immense adoration of a large scientific community because of their multifaceted applications, including organic light-emitting diodes (OLEDs), organic photovoltaics, night vision, optical telecommunication, and also in biolabelling and bioimaging. [1][2][3][4][5][6][7] In reality, the earth absorbs more than 50% of solar energy in the red and NIR-regime; 8 hence the invention of pure red and NIR-emitting chromophores with desirable properties has emerged as a promising research area in material chemistry. Primarily, the idea behind the design of NIR-emitting materials originated from rare-earth metals and transition metal complexes which also faced long-term problems in applicability because of their low availability, high cost, and fabrication issue.…”