Premixed Exciplex Co‐Host for Constructing High‐Performance Organic Light‐Emitting Diodes

Abstract Exciplex, characterized by intermolecular charge transfer and thermally activated delayed fluorescence (TADF) properties, plays a significant role in organic light‐emitting diodes (OLEDs), particularly as co‐hosts. The rapid rate of reverse intersystem crossing (RISC) and balanced carrier mobility contribute to improved efficiency and suppressive efficiency roll‐off at high current density. Despite these advantages, the fabrication of devices using two‐component exciplexes is challenging, especially when the emitting layers require the simultaneous evaporation of three or four materials from separate crucibles. To address this issue, a pair of premixed exciplex co‐hosts is developed and utilized as the co‐host for Ir(ppy) 3 . The consistent performance of continuous parallelly fabricated devices with the same premixed co‐host sample indicates the long‐term stability of the premixed exciplex co‐host and the stable evaporation ratio of the electron donor and electron acceptor molecules. The devices achieve maximum luminance over 250 000 cd m −2 , a maximum external quantum efficiency of 21.9%, a regardless efficiency roll‐off of 4.6% at 10 000 cd m −2 , along with a prolonged operational LT 95 (lifetime to 95% of the initial luminance) of 165 h at the current density of 10 mA cm −2 . Further enhancement in device performance is observed through co‐doping a multiple resonance TADF (MR‐TADF) material in the emitting layer, underscoring the significant potential for industrial application.