Regulating energy gap in Ir-based ionic complexes to generate near-infrared emissions: Application in solid-state light-emitting electrochemical cells

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Vol. 469; p. 144055
• Main Authors: Lin, Yan-Ding, Hsiao, Pei-Wan, Chen, Wun-Yu, Wu, Sih-Yu, Zhang, Wei-Min, Lu, Chin-Wei, Su, Hai-Ching
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.08.2023
• ISSN: 1385-8947
• DOI: 10.1016/j.cej.2023.144055

[Display omitted] •Investigate a series of cationic iridium complexes with extremely small energy gaps, with 2,2'-bibenzo[d]thiazole fixed as N^N ligand moiety mainly controlling the LUMO energy level, changing a series of C^N ligands.•All targeted complexes exhibited deep red/NIR phosphorescence, and these combined devices provided emission peaks at 690–730 nm and were applied as components in LECs, exhibiting a maximum EQE of 1.78% in electroluminescence devices.•Using a host-guest emission system with the iridium complex YIr as the host and complex TBBI as the guest, the highest EQE of LECs could be further enhanced to more than 2.34%, which is the highest value reported for NIR LECs. Solid-state light-emitting electrochemical cells (LECs) exhibit high potential for commercial electronics owing to their simple solution-processable device architectures, low-voltage operation, and compatibility with inert metal electrodes. However, the low device efficiency of most deep-red and near-infrared (NIR) LECs hinders their application (external quantum efficiency (EQE) < 1.00%). In this study, we demonstrate a simple method to tune the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of iridium-based ionic transition metal complexes (iTMCs) to generate NIR emissions. We investigate a series of cationic iridium complexes with small energy gaps, with 2,2′-bibenzo[d]thiazole fixed as N^N ligand moiety mainly controlling the LUMO energy level, changing a series of C^N ligands. All complexes exhibited deep red/NIR phosphorescence, and these combined devices provided emission peaks at 690–730 nm and were applied as components in LECs, exhibiting a maximum EQE of 1.78% in electroluminescence devices. Using a host–guest emission system with the iridium complex YIr as the host and complex TBBI as the guest, the highest EQE of LECs could be further enhanced to>2.34%, which is the highest value reported for NIR LECs.