IMPROVED EFFICIENCY IN POLYMER LIGHT-EMITTING-DIODES USING AIR-STABLE ELECTRODES

By placing an electron transport layer between the semiconducting polymer and the metallic contact, we have achieved improved efficiencies for yellow light-emitting diodes (LEDs) fabricated with poly(2,5-bis(cholestanoxy)-1,4-phenylene vinylene) as the electroluminescent layer and with aluminum and indium as the electron injecting electrodes. Quantum efficiencies of LEDs with the electron transport layer and an aluminum electrode are about 0.25% photons per electron, better by a factor of five than similar devices made without the electron transport layer; quantum efficiencies of LEDs with the electron transport layer and an indium electrode are about 0.4% photons per electron, better by a factor of two than devices without the electron transport layer.