An undoped electrophosphorescent organic light-emitting diode is fabricated using a pure platinum(Ⅱ)(2-phenylpyridinato-N, C2) (3-benzoyl-camphor) [(ppy)pt(bcam)] phosphorescent layer acting as the emitting layer. A maximum power efficiency ηp of 6.62lm/W and current efficiency of 14.78cd/A at 745 cd/m2 are ob-tained from the device. The roll-off percentage of ηp of the pure phosphorescent phosphor layer device is reduced to 5% at a current density of 20 mA/cm2, which is about 11% for conventional phosphorescent devices. The low roll-off efficiency is attributed to the phosphorescent material, which has the molecular structure of a strong steric hindrance effect.