The secondary kinetic isotope effects (KIEs) of red phosphorescent Ir(III) complexes and the corresponding devices have been investigated. The selective deuterated red emitters show negligible influence on the luminescent spectra, but have positive effects on the quantum efficiencies and stabilities in the devices. As secondary KIEs predicted, the photolysis coinciding with the electrolysis of the deuterated complexes in the devices, measured via decreasing of luminescent intensity, are reduced in rate. An about 33% increase of the device working lifetime could be readily obtained with the strategy of selective deuteration on the emitter complexes. The findings demonstrate the importance of the isotopic effect on the performance improvement of organic light emitting devices and will also trigger the study on organic optoelectronic materials via isotopic tools.