Published online by Cambridge University Press: 14 January 2011
Both luminous efficiency and lifetime in blue fluorescence organic lightemitting devices (OLEDs) have been improved by modified HTMs with higherLUMO energy levels. The LUMO energy levels of HTM were increased bymodifying substituent in HTM molecules. Two HTMs containing ortho and metabiphenyl substituent and one HTM containing thiophene substituent weresynthesized via palladium catalyzed amine coupling reactions to compare witha para biphenyl substituent HTM-1 as a standard molecule. According to TDDFTcalculations, these three modified HTMs showed 0.05-0.15 eV higher LUMOenergy levels compared to the para biphenyl substituent HTM-1. The luminousefficiency and the lifetime (LT90) of OLEDs using HTM-2 at 500 cd/m2 have been enhanced up to 20 % and 52 %, respectively,compared to the standard device using HTM-1.