New Insights into Tunable Volatility of Ionic Materials through Counter‐Ion Control

Recent development in the field of small molecular materials has led to great advances in the performance of vacuum‐evaporated organic light‐emitting diodes. However, as a significant class of phosphorescent emitters, ionic transition metal complexes are seldom sublimable due to the inherent ionic nature and low vapor pressure, restricting their applications in state‐of‐the‐art devices fabricated by vacuum evaporation deposition. Here a facile, feasible and versatile strategy is shown to tune the volatility of ionic transition metal complexes through counter‐ion control. By introducing counter‐ions with large steric hindrance and well‐dispersed charges, a series of evaporable ionic iridium complexes are developed, and efficient vapor‐processed devices with a high brightness, small efficiency roll‐off, and polychromic emission ranging from deep‐blue to red‐orange are achieved. Our findings unlock the utilization of ionic functional materials in vacuum‐evaporated devices, and may open new doors for modern electronic materials technology.