Orange-red- and white-emitting diodes fabricated by vacuum evaporation deposition of sublimable cationic iridium complexes

Abstract

Two novel red-emitting cationic iridium complexes, [Ir(ppy)₂(pop)][B(5fph)₄] (1) and [Ir(ppy)₂(pop)][BArF₂₄] (2), have been developed, where ppy is 2-phenylpyridine, pop is 2-(5-phenyl-1-1,3,4-oxadiazol-2-yl)pyridine, [B(5fph)₄]⁻ is tetrakis(pentafluorophenyl)borate and [BArF₂₄]⁻ is tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, respectively. Photophysical properties of 1 and 2 in both solution and neat film were fully investigated, along with their photochemical, thermal and electrochemical stability. Interestingly, by introducing bulky tetraphenylborate derivatives as negative counter-ions, the volatility of 1 and 2 has been extremely improved, enabling fabrication of organic light-emitting diodes (OLEDs) by vacuum evaporation deposition. By doping these two sublimable cationic emitters into a DIC-TRZ (2,4-diphenyl-6-bis(12-phenylindolo[2,3-a]carbazole-11-yl)-1,3,5-triazine) host, we succeeded in the preparation of orange-red-emitting devices with a peak wavelength of 596 nm. 1-Based OLEDs showed a current efficiency of 4.5 cd A⁻¹ and maximum brightness of 19.4 × 10³ cd m⁻², whereas 2-based OLEDs furnished a higher efficiency of 5.1 cd A⁻¹. Then, we attained a white emission by doping 1 or 2 into a TCTA (4,4′,4′′-tris(carbazol-9-yl)triphenylamine) host at low concentrations. The 1-based white device featured a high colour rendering index (CRI) of 86 and good Commission International de L'EClairage (CIE) coordinates of (0.33, 0.34), quite close to the equal-energy-white-point (i.e., CIE_x,y = 0.33, 0.33), and the 2-based white device showed a rather higher CRI of 89. To the best of our knowledge, this is the first report of white OLEDs fabricated by vacuum evaporation deposition of sublimable cationic iridium complexes, indicating their great potential for use in full-colour flat-panel display and lighting applications.