Phosphorescent organic light emitting diodes were fabricated that show high efficiencies with commercially viable lifetimes at display brightnesses of tens of thousands of hours at room temperature. We investigate here the performance of theses devices at elevated temperatures. We demonstrate that devices containing phosphorescent dopants can be operated at temperatures up to 130 degreesC. We also demonstrate improved device performance due to thermal treating e.g. a red phosphorescent device that decays by only 10% in the first 5500 h of operation driven with an initial luminance of 300 cd/m(2). (C) 2004 Elsevier B.V. All rights reserved.