We report a systematic comparison study of 3,5-di(N-carbazolyl)tetraphenyisilane (SimCP) and N,N'-dicarbazolyl-3,5-benzene (mCP), which are used as the host materials for phosphorescent blue dopants in organic light-emitting diodes (OLEDs). On the basis of photoexcitation emission spectroscopy, thermal stability analysis, photoelectron analysis, charge transport measurements, and molecular dynamics (MD) simulations, we conclude that the non-pi-conjugated meta-substituted triphenylsilyl moiety of SimCP exerts a unique hindering effect on the molecular packing characteristics in the condensed phase. The chemical origin of the superior performance of SimCP over mCP is revealed, and is expected to be helpful for the molecular design of effective host materials for enhancing the performance of blue phosphorescent OLEDs.