6‐4: Late‐News Paper: Realizing Deep Blue Emission in Blue Phosphorescent Organic Light‐Emitting Diodes

The origin of spectrum broadening in blue phosphorescent organic light‐emitting diodes (OLEDs) was investigated in order to improve color purity of the OLED device aiming to realize efficient blue phosphorescent OLED with deep blue emission. Assuming the formation of exciplex between host and guest (H‐G) material from intermolecular charge transfer (CT) state of the two, the experiment was performed controlling the distance between H‐G for the verification. The exciplex formation was observed dependent on the distance of H‐G, indicating that the spectrum broadening occurred due to H‐G CT state. The critical distance to avoid H‐G CT state was found which can be further utilized in designing host and dopant materials for blue phosphorescent OLEDs. The EL efficiency and the stability of the blue phosphorescent device were enhanced by 1.2 and 5 times, respectively, by minimizing H‐G CT state.