Sky-blue-emitting cationic iridium complexes with oxadiazole/triazine-type counter-anions and their use for efficient solution-processed organic light-emitting diodes

Counter-anion control has emerged as a facile approach to tune the properties of cationic iridium complexes for optoelectronic applications. Here we report sky-blue-emitting cationic iridium complexes with electron-deficient oxadiazole/triazine-type counter-anions and their use for highly efficient solution-processed organic light-emitting diodes (OLEDs). A sky-blue-emitting complex [Ir(meoppy)(2)(dmapzpy)](+) (meoppy is 4-methoxy-2-phenylpyridine and dmapzpy is 4-dimethylamino-2-(1H-pyrazol-1-yl)pyridine) has been developed as the phosphorescent cation. Hexafluorophosphate (PF6-), 3,5-bis(5-(4-(tert-butyl)phenyl)-1,3,4-oxadiazol-2-yl) benzenesulfonate (OXD-7-SO3-), 4-(4,6-diphenyl-1,3,5-triazin-2-yl)benzenesulfonate (TRZ-p-SO3-) and 3-(4,6-diphenyl-1,3,5-triazin-2-yl)benzenesulfonate (TRZ-m-SO3-) have been developed as the counter-anions in complexes R, 1, 2 and 3, respectively. In doped films, the complexes afford similar sky-blue emission peaked at around 472 nm with high phosphorescent efficiencies of around 0.80. Solution-processed, double-layer OLEDs using the complexes as dopants afford sky-blue electroluminescence peaked at around 476 nm. The devices using complexes 1-3 show largely enhanced performances compared to the device using the reference complex R, owing to the improved carrier-recombination balance imparted by the electron-trapping effects of the oxadiazole/triazine type counter-anions. The devices based on complexes 2 and 3 exhibit higher performances than that based on complex 1, because of the stronger electron-trapping effects of TRZ-p-SO3- and TRZ-m-SO3- compared to OXD-7-SO3-. The double-layer device using complex 3 shows a peak current efficiency of 29.4 cd A(-1) and an external quantum efficiency of 12.4%, which are the highest for blue OLEDs using cationic iridium complexes reported so far.

Automated summary

By controlling the oxadiazole/triazine type counter-anions, sky-blue-emitting cationic iridium complexes with electron-trapping effects have been developed for highly efficient solution-processed organic light-emitting diodes (OLEDs). These complexes exhibit significant enhancement in device performance compared to the reference complex, with the highest peak current efficiency and external quantum efficiency reported for blue OLEDs using cationic iridium complexes.