Highly efficient green polymer light‐emitting diodes through interface engineering

Abstract

Abstract— By interface engineering, we have improved the quantum efficiency for green polyfluorene polymer light‐emitting diodes by three fold: the efficiency improved from 9 to 28 cd/A. This interface engineering was achieved by inserting a thin layer of calcium (2) acetylacetonate, denoted as Ca(acac) 2 , at the polymer/metal cathode interface. The Ca(acac) 2 layer behaves in a multifunctional way. It assists the electron injection by lowering the electron‐injection barrier. In the meanwhile, hole injection is enhanced by the accumulated electrons in the polymer layer. This effect is believed to lower the barrier height for hole‐injection through the Schottky effect. Finally, the Ca(acac) 2 layer works as a hole block layer to block the holes. As a result of the charge balance and charge confinement, the device quantum efficiency increases dramatically.