A device for achieving reduced driving voltage and enhanced color stability under high luminance conditions includes an anode and cathode arranged on a substrate to be opposite each other, a charge generation layer between the anode and the cathode, a first stack formed between the anode and the charge generation layer and including a first light emitting layer, and a second stack formed between the charge generation layer and the cathode and including a second light emitting layer in which first and second hosts are doped with phosphorescent dopant, a HOMO level of the first host is greater than that of the second host, and a LUMO level of the first host is greater than an LUMO level of the second host.