An organic light emitting device (200, 300) comprising: an anode (215, 225); a cathode; and a first emissive layer (235, 335) disposed between the anode (215, 225) and the cathode, the first emissive layer (235, 335) consisting of an electron transporting compound and a phosphorescent emissive dopant compound; wherein the phosphorescent emissive dopant compound has a concentration gradient in the emissive layer (235, 335), characterized in that the concentration gradient varies according to one or more of the following: (i) linearly towards the cathode side of the first emissive layer (235, 335); (ii) non-linearly towards the cathode side of the first emissive layer (235, 335), wherein said non-linearity corresponds to a polynomial function selected from the group consisting of a quadratic function, a cubic function, or a higher order function; and (iii) a step wise form; wherein when the concentration gradient varies in a step wise form, the phosphorescent emissive dopant compound is dispersed in the emissive layer (235, 335) as a plurality of high concentration dopant regions and as a plurality of low concentration dopant regions; or when the concentration gradient varies in a step wise form, the phosphorescent emissive dopant compound is dispersed in the emissive layer (235, 335) as a plurality of first dopant regions and as a plurality of second dopant regions, and the first dopant regions are wider than the second dopant regions. an anode (215, 225); a cathode; and a first emissive layer (235, 335) disposed between the anode (215, 225) and the cathode, the first emissive layer (235, 335) consisting of an electron transporting compound and a phosphorescent emissive dopant compound; wherein the phosphorescent emissive dopant compound has a concentration gradient in the emissive layer (235, 335), characterized in that the concentration gradient varies according to one or more of the following: (i) linearly towards the cathode side of the first emissive layer (235, 335); (ii) non-linearly towards the cathode side of the first emissive layer (235, 335), wherein said non-linearity corresponds to a polynomial function selected from the group consisting of a quadratic function, a cubic function, or a higher order function; and (iii) a step wise form; (i) linearly towards the cathode side of the first emissive layer (235, 335); (ii) non-linearly towards the cathode side of the first emissive layer (235, 335), wherein said non-linearity corresponds to a polynomial function selected from the group consisting of a quadratic function, a cubic function, or a higher order function; and (iii) a step wise form; wherein when the concentration gradient varies in a step wise form, the phosphorescent emissive dopant compound is dispersed in the emissive layer (235, 335) as a plurality of high concentration dopant regions and as a plurality of low concentration dopant regions; or when the concentration gradient varies in a step wise form, the phosphorescent emissive dopant compound is dispersed in the emissive layer (235, 335) as a plurality of first dopant regions and as a plurality of second dopant regions, and the first dopant regions are wider than the second dopant regions.