Origin of improved stability in green phosphorescent organic light-emitting diodes based on a dibenzofuran/spirobifluorene hybrid host

A highly efficient and stable green phosphorescent organic light-emitting diode (PHOLED) was fabricated by using a new dibenzofuran/spirobifluorene hybrid material (named as DBFSF2) as the host material. The DBFSF2-based PHOLEDs exhibited slightly better electroluminescence efficiency than that in the conventional host material 4,4′-bis(carbazol-9-yl)biphenyl (CBP)-based ones. Moreover, further studies demonstrated that the DBFSF2-based PHOLEDs had a better stability with about 1.5 times improvement in half lifetime compared with that of CBP-based ones. To investigate the mechanism behind the enhanced stability in the DBFSF2-based PHOLEDs, the evaluations of dark spots growth, film crystallization properties and carrier recombination zone were carried out.