Benzimidazole-triazine based exciplex films as emitters and hosts to construct highly efficient OLEDs with a small efficiency roll-off

Although efficient exciplex-based organic light-emitting diodes (OLEDs) with simple device structures have shown great progress recently, highly efficient electron acceptor materials are still rare. Here, a series of newly developed electron acceptors for exciplex-OLEDs composed of benzimidazole and triazine hybrids are discussed. All three compounds display a triplet energy of 2.67-2.69 eV, ensuring a high photoluminescence quantum yield of 78.0-89.7% when mixed with an electron donor (TAPC: 4,4 '-cyclohexylidenebis[N,N-bis(p-tolyl)aniline]). Exciplex-based OLEDs with these electron acceptors and TAPC blend films as the emitting layers exhibit low driving voltages of 2.6-3.0 V at 100 cd m(-2) and 3.1-4.2 V at 1000 cd m(-2). High efficiencies of 53.2-80.1 lm W-1 and 39.7-60.1 cd A(-1) are obtained, and the highest external quantum efficiencies (EQE) are 12.5-18.4%. Green electro-phosphorescent emitters are also fabricated with exciplex-based cohosts by doping with tris(2-phenylpyridine)iridium (Ir(ppy)(3)), one of which shows the highest EQE of 29.6%, and the EQE can be maintained at 27.4% at 5000 cd m(-2). Therefore, the benzimidazole-triazine electron acceptors show promise as exciplex emitters and cohosts for OLEDs.