An organic light-emitting includes a first electrode having a work function greater than about 4.9 eV and less than about 5.2 eV, a second electrode facing the first electrode, an organic layer disposed between the first electrode and the second electrode and including an emission layer, a hole transport region disposed between the first electrode and the emission layer, wherein the hole transport region includes a first hole transport layer including a first hole-transporting material, and the first hole transport layer is substantially free of a p-dopant.