A display device comprising: a substrate; two pixel circuits over the substrate spaced apart from each other with a transmission area therebetween, each of the two pixel circuits including a transistor and a storage capacitor (Cst); two display elements (OLED) respectively electrically coupled to the two pixel circuits; a bottom metal layer between the substrate and the two pixel circuits and including a through hole (BML-TH) corresponding to the transmission area; an encapsulation member (300A, 300B) over the two display elements (OLED); and an optical functional layer over the encapsulation member (300A, 300B), wherein the optical functional layer includes: a first layer including a first opening (510OP1), second openings (510P2), and a first slope portion, the first opening (510OP1) corresponding to the transmission area, the second openings (510P2) corresponding to each of the two display elements (OLED), and the first slope portion being around the transmission area; and a second layer on the first layer and having a refractive index greater than a refractive index of the first layer, wherein the first opening (510OP1) and the second opening (510OP2) have the shape of a through hole through the first layer (510OP1), or have the shape of a blind hole such that a thickness of the first layer in the first opening (510OP1) and the second opening (510OP2) is less than a thickness of a remainder of the first layer. a substrate; two pixel circuits over the substrate spaced apart from each other with a transmission area therebetween, each of the two pixel circuits including a transistor and a storage capacitor (Cst); two display elements (OLED) respectively electrically coupled to the two pixel circuits; a bottom metal layer between the substrate and the two pixel circuits and including a through hole (BML-TH) corresponding to the transmission area; an encapsulation member (300A, 300B) over the two display elements (OLED); and an optical functional layer over the encapsulation member (300A, 300B), wherein the optical functional layer includes: a first layer including a first opening (510OP1), second openings (510P2), and a first slope portion, the first opening (510OP1) corresponding to the transmission area, the second openings (510P2) corresponding to each of the two display elements (OLED), and the first slope portion being around the transmission area; and a second layer on the first layer and having a refractive index greater than a refractive index of the first layer, wherein the first opening (510OP1) and the second opening (510OP2) have the shape of a through hole through the first layer (510OP1), or have the shape of a blind hole such that a thickness of the first layer in the first opening (510OP1) and the second opening (510OP2) is less than a thickness of a remainder of the first layer. a first layer including a first opening (510OP1), second openings (510P2), and a first slope portion, the first opening (510OP1) corresponding to the transmission area, the second openings (510P2) corresponding to each of the two display elements (OLED), and the first slope portion being around the transmission area; and a second layer on the first layer and having a refractive index greater than a refractive index of the first layer, wherein the first opening (510OP1) and the second opening (510OP2) have the shape of a through hole through the first layer (510OP1), or have the shape of a blind hole such that a thickness of the first layer in the first opening (510OP1) and the second opening (510OP2) is less than a thickness of a remainder of the first layer.