Homoleptic Tris-Cyclometalated Iridium Complexes with Substituted <i>o</i>‑Carboranes: Green Phosphorescent Emitters for Highly Efficient Solution-Processed Organic Light-Emitting Diodes KimYejin ParkSunghee LeeYoung Hoon JungJaehoon YooSeunghyup LeeMin Hyung 2016 Homoleptic tris-cyclometalated iridium complexes, <i>fac</i>-Ir­[5-(2-RCB)­ppy]<sub>3</sub> (<b>3a</b>–<b>3c</b>; CB = <i>o</i>-carboran-1-yl; ppy = 2-phenylpyridinato-C<sup>2</sup>,N; R = H (<b>3a</b>), Me (<b>3b</b>), <sup><i>i</i></sup>Bu (<b>3c</b>)) with 2-R-substituted <i>o</i>-carboranes at the 5-position of the ppy ligand, were prepared and characterized. X-ray diffraction analysis of <b>3a</b> and <b>3c</b> revealed that the three C^N ligands adopt a <i>fac</i>-arrangement around the Ir atom and that the carboranyl C–C bond distance increases with increasing steric effects of the 2-R substituent. The phosphorescence wavelengths of the complexes were apparently blue-shifted by ca. 20 nm (λ<sub>em</sub> = 487–493 nm) compared to that of the parent <i>fac</i>-Ir­(ppy)<sub>3</sub> (<b>4</b>; λ<sub>em</sub> = 508 nm). In particular, <b>3a</b>–<b>3c</b> were highly emissive in toluene, and the phosphorescence quantum efficiencies of <b>3a</b> and <b>3b</b> (Φ<sub>PL</sub> = 0.95–0.98) were comparable to that of <b>4</b>. Solution-processed electroluminescent devices incorporating <b>3a</b>–<b>3c</b> as emitters displayed green light with high performance, and devices based on the <b>3c</b> dopant showed the highest performance. In particular, the devices based on <b>3c</b> exhibited performance more than double of that of the device based on <b>4</b> in terms of current efficiency (29.6 cd/A for <b>3c</b> vs 15.8 cd/A for <b>4</b> at 4 wt % Ir and 1000 cd/m<sup>2</sup>), power efficiency (11.0 lm/W for <b>3c</b> vs 6.3 lm/W for <b>4</b>), and external quantum efficiency (10.2% for <b>3c</b> vs 4.7% for <b>4</b>) over a wide range of luminance. The higher PL quantum yields of doped host films with <b>3c</b> than those with <b>4</b> at high dopant concentrations above 8 wt % suggested that along with high phosphorescence quantum efficiency, the steric bulkiness of the 2-<sup><i>i</i></sup>Bu-substituted <i>o</i>-carborane in <b>3c</b> plays a crucial role in improving device performance.