OLEDs are composed of organic semiconductors sandwiched between positive (anode) and negative (cathode) electrodes. An OLED device consists of an anode made of transparent indium tin oxide (ITO), three organic layers - a hole transport layer (HTL), emitting layer (EML), and electron transport layer (ETL) - and a silver cathode. These are all fabricated on a glass substrate, which light passes through when the device is turned on.
When current is applied, electrons are injected at the cathode and holes at the anode. Electrons and holes travel toward each other through the layers, combining in the emissive layer to release energy in the form of photons. This happens quickly while current is flowing, causing a stream of continuous light.
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