The development of the triazine derivatives as the n-type (electron transport type) host for long device lifetime in deep blue phosphorescent organic light-emitting diodes (PhOLEDs) was studied by synthesizing two hosts with dibenzofuran and triphenylsily blocking groups. The triazine core was located at the center of the molecule and the triphenylsilyl group behaved as the blocking group of the planar core. The dibenzofuran was also attached to the triazine core for electron transport and high triplet energy. Two hosts with different number of dibenzofuran and tripheynylsilyl units were synthesized and the number of triphenylsilyl group was critical to the device lifetime results. The two hosts showed high external quantum efficiency over 20%, but the device lifetime was doubled by introducing two triphenylsilyl units instead of one triphenylsilyl group. A device lifetime of 2200 h at 100 cd/m2 was achieved using the new host. It was revealed that enlarging the intermolecular distance by inserting two bulky groups in the hosts had positive effects on increasing the device lifetime.