OLED makes use of the property that organic materials illuminate when voltage is supplied.
R, G, B can illuminate according to the organic materials so that Full color can be realized.
As a self-light emitting diode, it has high level of brightness/ color purity.

When power is supplied, electrons move and the current begins to flow: Electrons(-) from the Cathode move toward the Emitting Layer by the help of the Electron Transfer Layer, on the other hand, Holes(+: state of electrons released) from the Anode move toward the Emitting Layer by the help of the Hole Transfer Layer.

Electrons and Holes converged at the Emitting Layer of organic materials generate excitation with high level of energy when the excitation falls down to the lower energy state creating light.
The color of the light varies according to the organic materials forming the Emitting Layer, and Full color can be represented by each organic material emitting R,G,B colors. Contrary to LCD with the simple function of open/closing pixels, OLED utilizes self light-emitting organic materials.