Vladimir Bulovic a Electrical Engineering & Computer from Mit are showing a interesting video how OLED Displays work with using a glowing pickle.

OLEDs are nothing more than an electrically active organic material sandwiched between an anode (a electron-expelling electrode) and a cathode (an electron-receiving electrode). When an electric current runs through the system, the anode sends electrons to the cathode, creating a current through the organic material. This charges the organic material, and when positive and negative charges hit the same molecule, it releases a photon, which we perceive as glowing.
Source: MIT