An organic light emitting diode display device comprising: a substrate ; a first electrode disposed on the substrate ; a pixel defining layer disposed on the substrate , the pixel defining layer overlapping an edge of the first electrode ; an organic light emitting layer disposed on the first electrode ; a second electrode disposed on the organic light emitting layer ; and a thin film encapsulation layer (301; 302; 303; 304; 305; 306; 307) disposed on the second electrode , wherein the thin film encapsulation layer (301; 302; 303; 304; 305; 306; 307) comprises: at least one inorganic layer (310; 330; 350); and at least one organic layer (320; 340) that is disposed alternately with the at least one inorganic layer (310; 330; 350), wherein the at least one organic layer (320; 340) comprises: a low refractive index layer overlapping the organic light emitting layer ; and a high refractive index layer disposed on the low refractive index layer , the high refractive index layer having a higher refractive index than a refractive index of the low refractive index layer ; wherein the high refractive index layer comprises a convex surface protruding toward the organic light emitting layer ; wherein the low refractive index layer comprises a concave surface corresponding to the convex surface of the high refractive index layer , characterised in that a height (d1) of at least a portion of the concave surface of the low refractive index layer with respect to the surface of the substrate is less than the height (d1) of the pixel defining layer with respect to the surface of the substrate . a substrate ; a first electrode disposed on the substrate ; a pixel defining layer disposed on the substrate , the pixel defining layer overlapping an edge of the first electrode ; an organic light emitting layer disposed on the first electrode ; a second electrode disposed on the organic light emitting layer ; and a thin film encapsulation layer (301; 302; 303; 304; 305; 306; 307) disposed on the second electrode , wherein the thin film encapsulation layer (301; 302; 303; 304; 305; 306; 307) comprises: at least one inorganic layer (310; 330; 350); and at least one organic layer (320; 340) that is disposed alternately with the at least one inorganic layer (310; 330; 350), at least one inorganic layer (310; 330; 350); and at least one organic layer (320; 340) that is disposed alternately with the at least one inorganic layer (310; 330; 350), wherein the at least one organic layer (320; 340) comprises: a low refractive index layer overlapping the organic light emitting layer ; and a high refractive index layer disposed on the low refractive index layer , the high refractive index layer having a higher refractive index than a refractive index of the low refractive index layer ; a low refractive index layer overlapping the organic light emitting layer ; and a high refractive index layer disposed on the low refractive index layer , the high refractive index layer having a higher refractive index than a refractive index of the low refractive index layer ; wherein the high refractive index layer comprises a convex surface protruding toward the organic light emitting layer ; wherein the low refractive index layer comprises a concave surface corresponding to the convex surface of the high refractive index layer , characterised in that a height (d1) of at least a portion of the concave surface of the low refractive index layer with respect to the surface of the substrate is less than the height (d1) of the pixel defining layer with respect to the surface of the substrate . <EOS>