​In this work, the harmful effect of triplet excitons on the lifetime of poly(p-phenylene vinylene) (PPV)-based organic light emitting diodes is demonstrated. A model system has been designed in which the triplet population in a PPV derivative is increased by blending the polymer with the triplet sensitizer platinum (II) octaethylporphyrine ketone (PtOEPK). The increase in the triplet concentration of the polymer affects both the initial decay and the long-term evolution of luminance and leads to a drastic acceleration of device degradation, reflected in a dramatically shortened lifetime.