![]() ![]() In this system, triplet excitons are efficiently upconverted from a lowest triplet state (T 1) to the lowest excited singlet state (S 1) by a reverse intersystem crossing (RISC) process, governed by a small energy gap (Δ E ST) between the S 1 and T 1 states, resulting in a maximum η int of close to 100%. As an alternative approach, highly efficient thermally activated delayed fluorescence (TADF)-based OLEDs have recently been realized using simple aromatic compounds as an emitter 8. However, the weak metal–ligand coordination bonds result in a limited device lifetime in blue OLEDs 5, 6, 7. On the other hand, the utilization of phosphorescent emitters containing heavy metals such as Ir, Pt, Os, and Au enhanced intersystem crossing by the strong spin–orbit coupling (SOC), and these phosphorescent emitters can harvest not only singlet excitons but also triplet excitons, leading to an ideal η int of nearly 100% in OLEDs 3, 4. In OLEDs, the most important parameter is the internal quantum efficiency ( η int), which is theoretically limited to 25% in traditional fluorescence-based OLEDs, as only singlet excitons can be harvested under electrical excitation 1, 2. Organic light-emitting diodes (OLEDs) have been commercialized in flat panel displays and solid-state lighting applications, and significant efforts are still devoted to enhancing OLED performance. Further, the high maximum efficiency were retained to be 20.2% and 17.4% even at high luminance. An OLED utilizing this TADF emitter displayed deep-blue electroluminescence (EL) with CIE chromaticity coordinates of (0.14, 0.18) and a high maximum EL quantum efficiency of 20.7%. An extremely fast exciton lifetime of 750 ns was realized in a donor–acceptor-type molecular structure without heavy metal elements. Here, we report a deep-blue TADF emitter employing simple molecular design, in which an activation energy as well as spin–orbit coupling between excited states with different spin multiplicities, were simultaneously controlled. However, blue TADF emitters generally have long exciton lifetimes, leading to severe efficiency decrease, i.e., rolloff, at high current density and luminance by exciton annihilations in organic light-emitting diodes (OLEDs). Provisions of Child Labour and Adolescent Prohibition and Regulation Act.Aromatic organic deep-blue emitters that exhibit thermally activated delayed fluorescence (TADF) can harvest all excitons in electrically generated singlets and triplets as light emission. ![]() PM Modi Launches CHAMPIONS: Technology Platform to empower MSMEs.For MSME Udyam Registration, the official site is ![]()
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