An organic light emitting display device, comprising: an anode (202, 302, 402, 502, 602, 702, 802) on a substrate (201, 301, 401, 501, 601, 701, 801); a first emission part (210, 310, 410, 510, 610, 710) on the anode (202, 302, 402, 502, 602, 702, 802), the first emission part (210, 310, 410, 510, 610, 710) including a first emission layer (214, 314, 414, 514, 614, 714, 814) and a first electron transfer layer (216, 316, 416, 516, 616, 716, 816); a second emission part (220, 320, 420, 520, 620, 720, 820) on the first emission part (210, 310, 410, 510, 610, 710, 810), the second emission part (220, 320, 420, 520, 620, 720, 820) including a second emission layer (224, 324, 424, 524, 624, 724, 824) and a second electron transfer layer (226, 326, 426, 526, 626, 726, 826); and a cathode (204, 304, 404, 504, 604, 704, 804) on the second emission part (220, 320, 420, 520, 620, 720, 820), wherein at least one among the first electron transfer layer (216, 316, 416, 716, 816) and the second electron transfer layer (226, 326, 426, 726, 826) comprises a first material and a second material, and an absolute value of a low unoccupied molecular orbitals, LUMO, energy level of the first material is larger than an absolute value of a LUMO energy level of the second material, wherein the first material and the second material are mixed through co-deposition, wherein the organic light emitting display device further comprises an N-type charge generation layer (541, 641, 741, 841) between the first emission part (510, 610, 710, 810) and the second emission part (520, 620, 720, 820), wherein the N-type charge generation layer is formed of an organic layer doped with metal, and wherein the first electron transfer layer (516, 616, 716, 816) comprises a material having an energy bandgap which is 0.50eV to 1.00eV higher than an energy bandgap of a host included in the N-type charge generation layer (541, 641, 741, 841). an anode (202, 302, 402, 502, 602, 702, 802) on a substrate (201, 301, 401, 501, 601, 701, 801); a first emission part (210, 310, 410, 510, 610, 710) on the anode (202, 302, 402, 502, 602, 702, 802), the first emission part (210, 310, 410, 510, 610, 710) including a first emission layer (214, 314, 414, 514, 614, 714, 814) and a first electron transfer layer (216, 316, 416, 516, 616, 716, 816); a second emission part (220, 320, 420, 520, 620, 720, 820) on the first emission part (210, 310, 410, 510, 610, 710, 810), the second emission part (220, 320, 420, 520, 620, 720, 820) including a second emission layer (224, 324, 424, 524, 624, 724, 824) and a second electron transfer layer (226, 326, 426, 526, 626, 726, 826); and a cathode (204, 304, 404, 504, 604, 704, 804) on the second emission part (220, 320, 420, 520, 620, 720, 820), wherein at least one among the first electron transfer layer (216, 316, 416, 716, 816) and the second electron transfer layer (226, 326, 426, 726, 826) comprises a first material and a second material, and an absolute value of a low unoccupied molecular orbitals, LUMO, energy level of the first material is larger than an absolute value of a LUMO energy level of the second material, wherein the first material and the second material are mixed through co-deposition, wherein the organic light emitting display device further comprises an N-type charge generation layer (541, 641, 741, 841) between the first emission part (510, 610, 710, 810) and the second emission part (520, 620, 720, 820), wherein the N-type charge generation layer is formed of an organic layer doped with metal, and wherein the first electron transfer layer (516, 616, 716, 816) comprises a material having an energy bandgap which is 0.50eV to 1.00eV higher than an energy bandgap of a host included in the N-type charge generation layer (541, 641, 741, 841).