Investigation of degradation mechanism of phosphorescent and thermally activated delayed fluorescent organic light-emitting diodes through doping concentration dependence of lifetime

•Lifetime dependence on doping concentration in the phosphorescent and TADF organic light-emitting diodes.•Triplet–triplet annihilation as dominant degradation mechanism of phosphorescent devices.•Triplet–polaron annihilation as dominant degradation mechanism of TADF devices