Abstract
During the past decades, the development of emissive materials for organic light-emitting diodes (OLEDs) in infrared region has focused the interest of numerous research groups as these devices can find interest in applications ranging from optical communication to defense. To date, metal complexes have been most widely studied to elaborate near-infrared (NIR) emitters due to their low energy emissive triplet states and their facile access. In this review, an overview of the different metal complexes used in OLEDs and enabling to get an infrared emission is provided.
Highlights
During the past decades, a great deal of efforts has been devoted to improving the device-stacking as well as the materials used to fabricate organic light-emitting diodes (OLEDs)
Concerning phthalocyanine, of the results reported in this review reveals platinum complexes to be abandoned for the design of the metal cation introduced in the macrocycle can drastically impact the emission wavelength
Interest for iridium complexes is notably sustained by the remarkable performances obtained with visible LEDs
Summary
A great deal of efforts has been devoted to improving the device-stacking as well as the materials used to fabricate organic light-emitting diodes (OLEDs). In 2012, a breakthrough was achieved by Chihaya Adachi who evidenced the benefits of the third generation of emitters, that is, the Thermally Activated Delayed Fluorescence (TADF) emitters which could compete with the metal-based phosphorescent light-emitting materials while being metal-free [4] This evolution of structure is the result of the observation that the elongation of the excited state lifetime of emitters and the possibility to harvest both singlet and triplet excitons with phosphorescent and TADF materials can greatly improve the overall electroluminescence efficiencies of electroluminescent devices, an internal quantum efficiency (IQE) close to the unit being achievable. Due to their low energy gaps, device performances remain limited, and platinum complexes have been the most widely studied complexes for producing a deep red/NIR emission [25] Their square planar structures, their long-living excited-state lifetimes favorable to triplet-triplet annihilation have adversely impacted their practical use in OLEDs [26]. It has to be noticed that according to the Commission Internationale de l’Eclairage (CIE), the NIR emission extends from 700 to 1400 nm, the first value (700 nm) corresponding to the end of the response of the human eye [39]
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