Atomic layer deposited zirconium oxide electron injection layer for efficient organic light emitting diodes

Abstract In this work, we demonstrate efficient polyfluorene-based light emitting diodes on which conformal, thin ZrO 2 layers, formed by atomic layer deposition at a relatively low temperature (175 °C), in order to avoid introducing any damage in the organic under layer, efficiently inject electrons from their high lying conduction band to the polymer’s LUMO. An optimal thickness of 2 nm for ZrO 2 results in a threefold improvement in luminous current efficiency compared to the reference device. The relationship between the thickness of the ZrO 2 layer and the device operational characteristics is further investigated and the possible reasons for the improved device performance are discussed based on the experimental results obtained by a combination of photoemission spectroscopy and electrical/optical measurements.