A display device comprising a quantum dot electroluminescent device, the quantum dot electroluminescent device comprising: a first electrode and a second electrode facing each other; an emission layer, comprising a plurality of quantum dots, wherein the emission layer is disposed between the first electrode and the second electrode; a first charge auxiliary layer disposed between the first electrode and the emission layer; and an optical functional layer disposed on the second electrode on a side opposite the emission layer and having a thickness of about 30 nanometers to about 70 nanometers; wherein the first electrode comprises a reflecting electrode, wherein the second electrode is a light-transmitting electrode, wherein the emission layer emits a blue light and the thickness of the first charge auxiliary layer ranges from about 20 nanometers to about 50 nanometers; wherein an optical length, defined by the distance between the first electrode and optical functional layer, forms a microcavity such that light radiated by the plurality of quantum dots is resonated by repeatedly reflecting between the first electrode and the optical functional layer and then amplified into light of a predetermined wavelength, and wherein a refractive index of the optical functional layer is greater than or equal to a refractive index of the second electrode. a first electrode and a second electrode facing each other; an emission layer, comprising a plurality of quantum dots, wherein the emission layer is disposed between the first electrode and the second electrode; a first charge auxiliary layer disposed between the first electrode and the emission layer; and an optical functional layer disposed on the second electrode on a side opposite the emission layer and having a thickness of about 30 nanometers to about 70 nanometers; an emission layer, comprising a plurality of quantum dots, wherein the emission layer is disposed between the first electrode and the second electrode; a first charge auxiliary layer disposed between the first electrode and the emission layer; and an optical functional layer disposed on the second electrode on a side opposite the emission layer and having a thickness of about 30 nanometers to about 70 nanometers; wherein the first electrode comprises a reflecting electrode, wherein the second electrode is a light-transmitting electrode, wherein the emission layer emits a blue light and the thickness of the first charge auxiliary layer ranges from about 20 nanometers to about 50 nanometers; wherein an optical length, defined by the distance between the first electrode and optical functional layer, forms a microcavity such that light radiated by the plurality of quantum dots is resonated by repeatedly reflecting between the first electrode and the optical functional layer and then amplified into light of a predetermined wavelength, and wherein a refractive index of the optical functional layer is greater than or equal to a refractive index of the second electrode. wherein an optical length, defined by the distance between the first electrode and optical functional layer, forms a microcavity such that light radiated by the plurality of quantum dots is resonated by repeatedly reflecting between the first electrode and the optical functional layer and then amplified into light of a predetermined wavelength, and wherein a refractive index of the optical functional layer is greater than or equal to a refractive index of the second electrode.