An organic light emitting diode (OLED) display device, comprising: a substrate (100, 200, 300, 400); a first electrode (103, 201, 310, 403R, 403G, 403B) disposed on the substrate; an organic layer (104, 202, 311, 405R, 405G, 405B) disposed on the first electrode (103, 201, 310, 403R, 403G, 403B) and including an emission layer; a second electrode (105, 203, 312, 407) disposed on the organic layer (104, 202, 311, 405R, 405G, 405B); first (102, 204, 309, 402) and a second (101, 205, 308, 201) refraction layer, disposed either between the first electrode (103, 201, 310, 403R, 403G, 403B) and the substrate (100, 200, 300, 400) or on the second electrode (105, 203, 312, 407); wherein a refractive index of the first refraction layer (102, 204, 309, 402) is smaller than a refractive index of the second refraction layer (101, 205, 308, 201), and the first refraction layer (102, 204, 309, 402) has a thickness of 100 nm or less; and a third refraction layer either disposed between the second refraction layer (101, 205, 308, 201) and the substrate (100, 200, 300, 400), if the first (102, 204, 309, 402) and second (101, 205, 308, 201) refraction layers are disposed between the first electrode (103, 201, 310, 403R, 403G, 403B) through which light is emitted and the substrate (100, 200, 300, 400), or disposed on the second refraction layer (101, 205, 308, 201), if the first (102, 204, 309, 402) and second (101, 205, 308, 201) refraction layers are disposed on the second electrode (105, 203, 312, 407) through which light is emitted; wherein the third refraction layer has a refractive index that is the same as the refractive index of the first refraction layer (102, 204, 309, 402); characterised in that the first refraction layer directly contacts the first electrode or the second electrode; and wherein the thickness of the second refraction layer (101, 205, 308, 201) is from 150 nm to 350 nm. a substrate (100, 200, 300, 400); a first electrode (103, 201, 310, 403R, 403G, 403B) disposed on the substrate; an organic layer (104, 202, 311, 405R, 405G, 405B) disposed on the first electrode (103, 201, 310, 403R, 403G, 403B) and including an emission layer; a second electrode (105, 203, 312, 407) disposed on the organic layer (104, 202, 311, 405R, 405G, 405B); first (102, 204, 309, 402) and a second (101, 205, 308, 201) refraction layer, disposed either between the first electrode (103, 201, 310, 403R, 403G, 403B) and the substrate (100, 200, 300, 400) or on the second electrode (105, 203, 312, 407); wherein a refractive index of the first refraction layer (102, 204, 309, 402) is smaller than a refractive index of the second refraction layer (101, 205, 308, 201), and the first refraction layer (102, 204, 309, 402) has a thickness of 100 nm or less; and a third refraction layer either disposed between the second refraction layer (101, 205, 308, 201) and the substrate (100, 200, 300, 400), if the first (102, 204, 309, 402) and second (101, 205, 308, 201) refraction layers are disposed between the first electrode (103, 201, 310, 403R, 403G, 403B) through which light is emitted and the substrate (100, 200, 300, 400), or disposed on the second refraction layer (101, 205, 308, 201), if the first (102, 204, 309, 402) and second (101, 205, 308, 201) refraction layers are disposed on the second electrode (105, 203, 312, 407) through which light is emitted; wherein the third refraction layer has a refractive index that is the same as the refractive index of the first refraction layer (102, 204, 309, 402); characterised in that the first refraction layer directly contacts the first electrode or the second electrode; and wherein the thickness of the second refraction layer (101, 205, 308, 201) is from 150 nm to 350 nm.