The present invention relates to an organic electroluminescent device comprising a first electrode, at least one second electrode, at least one emission layer and at least one electron transport region, wherein the emission layer and the electron transport region are arranged between the at least one second electrode and the first and the electron transport region is arranged between the emission layer and the at least one second electrode, wherein the at least one electron transport region comprises a first electron transport layer, the first electron transport layer preferably not comprising an n-type dopant; and a performance enhancement layer, the performance enhancement layer having a refractive index of ≤1.6 at a wavelength of 1,200 nm; wherein the first electron transport layer is arranged between the emission layer and the performance enhancement layer; and the performance enhancement layer is arranged between the first electron transport layer and the at least one second electrode.