Spiro derivatives as electron-blocking materials for highly stable OLEDs

In this study, we introduced N-([1,1'-biphenyl]-2-yl)-N-(9,9-dimethyl-9H-fluoren-2-yl) spiro[dibenzo[a,d] [7] annulene-5,9'-fluoren]-2'-amine (BFS2A) and N-([1,1'-biphenyl] -2-yl)-N-(9,9-dimethyl-9H-fluoren-2-yespiro [dibenzo[a,d][7]annulene-5,9'-fluoren]-3-amine (BFS3A) as electron-blocking materials in organic light-emitting diodes (OLEDs). We verified that these materials have suitable optical properties as well as good electrochemical and thermal stability. Devices based on these materials also exhibited excellent charge balance, which corresponded to good device lifetime. Although BFS2A and BFS3A have similar molecular structures, OLEDs with these compounds as electron-blocking materials exhibited different performance, which we attributed to the differences in the modifying positions of the spiro backbone.