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

[Display omitted] • 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. [ABSTRACT FROM AUTHOR]