Novel Ortho‐Linkage Donor‐Acceptor Type Host Materials for Efficiently Red Phosphorescence Organic Light‐Emitting Diodes

Abstract High performance device is the key issue for organic light‐emitting diodes (OLEDs) industrialization. In this instance, efficient hosts, emitters, as well as other functional layer materials are essential for the realization of high‐performance OLEDs. Herein, we develop a series of D−A type host materials, TPATRZ , CzTRZ , and POXTRZ with ortho ‐linking strategy. The ortho ‐linkage makes TPATRZ , CzTRZ , and POXTRZ highly twisted conformations, which reducing the degree of intramolecular conjugation and maintain high triplet energies of these materials. The red phosphorescence organic light emitting diodes by using Ir(piq) 2 (acac) as dopant, TPATRZ , CzTRZ , and POXTRZ as host materials achieved relative high device performance with over 20 % external quantum efficiency and flat efficiency roll‐off. The EQEs of the champion devices remain above 22 % at the practical luminance (500 and 1000 cd m −2 ). The device hosted by POXTRZ achieved the highest external quantum efficiency of 24.0 %, as well as smallest efficiency roll‐off of 6.3 % at 1000 cd m −2 . These results further extend the possibilities of ortho ‐linkage D−A type host materials and make them have a promising application in OLEDs.