This study presents the synthesis and characterization of two spirobifluorenyl derivatives substituted with either triphenylmethyl (SB-C) or triphenylsilyl (SB-Si) moieties for use as host materials in phosphorescent organic light-emitting diodes (PHOLED). Both molecules have similar high triplet energies and large energy gaps. Blue Ir(tpz)3and green Ir(ppy)3phosphorescent devices were fabricated using these materials as hosts. Surprisingly,SB-Sidemonstrated superior charge-transporting ability compared toSB-C, despite having similar energies for their valence orbitals. In particular,SB-Siproved to be a highly effective host for both blue and green devices, resulting in maximum efficiencies of 12.6% for the Ir(tpz)3device and 9.6% for the Ir(ppy)3device. These results highlight the benefits of appending the triphenylsilyl moiety onto host materials and underscore the importance of considering the morphology of hosts in the design of efficient PHOLEDs.