Blue organic light-emitting diodes (OLEDs) with an emissive layer comprising 4–15 wt% FIrpic doped in bis(9-carbazolyl)benzene (mCP) were subjected to current stressing at 10–100 mA/cm2. The tests were conducted in either a continuous wave or pulsed mode to differentiate the thermal and nonthermal effects. The aged OLEDs exhibited a recombination zone shift toward the indium-tin-oxide anode, as manifested by a spectral change and a stretched exponential luminance decay whose rate was a strong function of the current density but nearly independent of the pulsing duty cycle. These behaviors suggest an aging process dominantly governed by defect-formation reactions in a narrow zone involving the emitting dye and stimulated by electric current, leading to enhanced hole trapping or electron detrapping. Broadening the recombination zone through increasing the FIrpic doping level and postannealing at 50 °C extended the lifetime by up to 3.6 times due to alleviated self-quenching and defect formation.