Near‐Infrared Light‐Emitting Diodes from Organic Radicals with Charge Control. Issue 21 (21st August 2022)

• Record Type: Journal Article
• Authors: Cho, Hwan‐Hee; Kimura, Shun; Greenham, Neil C.; Tani, Yuki; Matsuoka, Ryota; Nishihara, Hiroshi; Friend, Richard H.; Kusamoto, Tetsuro; Evans, Emrys W.
• Is Part Of: Advanced optical materials. Volume 10:Issue 21(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-08-21
• Subjects: energy transfer -- mixed hosts -- near‐infrared organic light‐emitting diodes -- organic radicals; Optical materials -- Periodicals; Photonics -- Periodicals; 620.11295
• DOI: 10.1002/adom.202200628
• Languages: English
• ISSNs: 2195-1071

Abstract

Abstract: Organic radicals with fluorescence from doublet‐spin energy manifolds circumvent efficiency limits from singlet–triplet photophysics in organic light‐emitting diodes (OLEDs). The singly occupied molecular orbital (SOMO) in radicals enables the higher potential performance. The SOMO also presents substantially lower energy frontier orbitals compared to conventional fluorescent emitters for device operation, which can cause severe electron trapping that limits the performance of radical OLEDs. To improve optoelectronic performance, electron donor–acceptor‐mixed hosts are used to control charge transport for enhanced radical electroluminescence by charge recombination on SOMO and frontier orbitals. The (2‐chloro‐3‐pyridyl)bis(2, 4, 6‐trichlorophenyl)methyl‐based radical is designed to test the charge‐controlled device architectures in OLEDs by transient analysis and device characterization studies. Efficient radical OLEDs with 4.7% maximum external quantum efficiency are reported—showing substantial advances in performance for OLEDs with peak emission beyond 800 nm. In addition, substantially improved performance at higher current density operation and more than two orders of higher lifetime stability are achieved with mixed hosts. These results enable pathways to infrared‐emitting devices with applications ranging from communications to bioimaging. Abstract : Unpaired electrons in radical emitters are shown to enable high electroluminescence efficiency in organic light‐emitting diodes (OLEDs), while also leading to severe charge trapping that limits overall performance. Here, electron donor–acceptor‐mixed hosts are employed with a novel radical emitter (TPA‐PyBTM′) to test charge transport‐controlled architectures that result in OLEDs with over 5% external quantum efficiency for 820 nm emission.