Sublimable cationic iridium(iii) complexes for red-emitting diodes with high colour purity. Issue 42 (13th October 2020)

• Record Type: Journal Article
• Authors: Liu, Ruihuan; Ma, Dongxin; Duan, Lian
• Is Part Of: Journal of materials chemistry. Volume 8:Issue 42(2020)
• Page Start: 14766
• Page End: 14772
• Publication Date: 2020-10-13
• Subjects: Materials -- Periodicals; Chemistry, Analytic -- Periodicals; Optical materials -- Research -- Periodicals; Electronics -- Materials -- Research -- Periodicals; 543.0284
• DOI: 10.1039/d0tc04126b
• Languages: English
• ISSNs: 2050-7526

Abstract

Abstract : Cationic iridium(iii ) complexes show great promise as phosphorescent materials due to their superior photophysical properties and electrochemical stabilities. Abstract : Cationic iridium(iii ) complexes show great promise as phosphorescent materials due to their superior photophysical properties and electrochemical stabilities. However, the previously reported red-emitting cationic iridium(iii ) complexes suffered from low photoluminescence quantum yields (PLQYs) of less than 35% and colour coordinates deviating from (0.67, 0.33) of the standard red emission, due to which the resulting organic light-emitting diodes (OLEDs) exhibited low external quantum efficiencies (EQEs) with undesirable colour purity. Here we report a cationic iridium(iii ) complex with diphenylquinoxaline-type cyclometalated ligands, achieving pure red emission with PLQYs over 80%. We investigate the photophysical properties both experimentally and theoretically, and find that there is a high MLCT (metal-to-ligand charge transfer) percentage in the excited states, leading to strong spin–orbit coupling and configuration interaction. We fabricate OLEDs based on this complex, achieving a high EQE of 10.3% with small efficiency roll-off at high luminance, and pure red emission with colour coordinates of (0.67, 0.33), close to the National Television System Committee (NTSC)-recommended standard. Our study demonstrates a strategy to tune the nature of excited states to develop sublimable cationic iridium(iii ) complexes with MLCT predominant mixing states, thereby realizing OLEDs with high efficiency and colour purity, which sheds light on their application in lighting and displays.