Electroplex hosts for highly efficient phosphorescent organic light-emitting diodes with extremely small efficiency roll-offs

Abstract

• Four bipolar molecules were designed and synthesized for accessing exciplex and electroplex host systems. • Highly efficient green PhOLED with EQE max of 29.9% was achieved. • Extremely small efficiency roll-offs (1.3% at 1,000 cd m −2 ; 5.4% at 5,000 cd m −2 ) were obtained. Host materials are of great significance to achieve high-performance host–guest organic light-emitting diodes (OLEDs) through restraining the exciton annihilation in the emissive layer. Herein, four bipolar molecules bearing benzothienocarbazole ( BTCz )/benzothienocarboline ( BTCb ) and benzimidazole ( Bi ) moieties were designed and synthesized. Using them as hosts, green phosphorescent OLEDs (PhOLEDs) with maximum current efficiency (CE max ) of 90.8 cd A −1 , power efficiency (PE max ) of 76.5 lm W −1 , and external quantum efficiency (EQE max ) of 27.9% were obtained. More importantly, it was found that these four molecules could be used as electron-donating materials to interact with electron-accepting triazine derivatives to form electroplexes. Employing these electroplexes as hosts, highly efficient green PhOLEDs with CE max of 104.4 cd A −1 , PE max of 85.1 lm W −1 , EQE max of 29.9%, and extremely small efficiency roll-offs (EQE = 29.5%, 1.3% roll-off at 1,000 cd m −2 ; EQE = 28.3%, 5.4% roll-off at 5,000 cd m −2 ) were achieved. The excellent device performances fully exhibit the promising potential of electroplexes as hosts for high-performing OLEDs.