An organic light emitting diode display device, comprising: a substrate on which first, second and third pixel regions are defined; a first electrode on the substrate in the first, second and third pixel regions; a hole auxiliary layer on the first electrode ; a first light emitting material layer on the hole auxiliary layer , the first light emitting material layer arranged to emit first light; an electron auxiliary layer on the first light emitting material layer ; a first charge generation layer and a second light emitting material layer between the first light emitting material layer and the electron auxiliary layer , the second light emitting material layer arranged to emit light having a same wavelength as the first light; a buffer layer between the first light emitting material layer and the first charge generation layer or between the first charge generation layer and the second light emitting material layer , the buffer layer being formed of a bipolar compound, wherein the bipolar compound includes an arylamine group and one of a heteroaryl group, a silicon group having an aromatic substituent and a sulfonyl group in a molecule; a second electrode on the electron auxiliary layer ; a color changing layer under the first electrode , wherein the color changing layer includes first, second and third portions (290a-c) corresponding to the first, second and third pixel regions, respectively, wherein the first portion is arranged to absorb the first light and output second light, the second portion is arranged to absorb the first light and output third light, and the third portion is arranged to allow the first light to pass therethrough; wherein the substrate is disposed between the color changing layer and the first electrode, wherein the first, second and third pixel regions include the first and second light emitting material layers emitting blue light as the first light. a substrate on which first, second and third pixel regions are defined; a first electrode on the substrate in the first, second and third pixel regions; a hole auxiliary layer on the first electrode ; a first light emitting material layer on the hole auxiliary layer , the first light emitting material layer arranged to emit first light; an electron auxiliary layer on the first light emitting material layer ; a first charge generation layer and a second light emitting material layer between the first light emitting material layer and the electron auxiliary layer , the second light emitting material layer arranged to emit light having a same wavelength as the first light; a buffer layer between the first light emitting material layer and the first charge generation layer or between the first charge generation layer and the second light emitting material layer , the buffer layer being formed of a bipolar compound, wherein the bipolar compound includes an arylamine group and one of a heteroaryl group, a silicon group having an aromatic substituent and a sulfonyl group in a molecule; a second electrode on the electron auxiliary layer ; a color changing layer under the first electrode , wherein the color changing layer includes first, second and third portions (290a-c) corresponding to the first, second and third pixel regions, respectively, wherein the first portion is arranged to absorb the first light and output second light, the second portion is arranged to absorb the first light and output third light, and the third portion is arranged to allow the first light to pass therethrough; wherein the substrate is disposed between the color changing layer and the first electrode, wherein the first, second and third pixel regions include the first and second light emitting material layers emitting blue light as the first light. <EOS>