An organic light-emitting diode (OLED) having first, second and third sub-pixels of different colors includes: a substrate; first and second electrodes; an organic emission layer (OEL) between the electrodes including a first OEL in the first sub-pixel, a second OEL in the second sub-pixel, and a common third OEL in the first, second and third sub-pixels; a hole transport layer (HTL) between the first electrode and OEL; a hole injection layer (HIL) between the first electrode and HTL; an intermediate layer between the HTL and HIL; a first optical thickness auxiliary layer (OTAL) between the first OEL and third OEL in the first sub-pixel and including a first hole transporting compound and a cyano group-containing compound; and a second OTAL including a second hole transporting compound between the third OEL and HTL in the first sub-pixel, and between the second OEL and HTL in the second sub-pixel.