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

In this work, we demonstrate efficient polyfluorene-based light emitting diodes on which conformal, thin ZrO2 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 ZrO2 results in a threefold improvement in luminous current efficiency compared to the reference device. The relationship between the thickness of the ZrO2 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.

In this work, we demonstrate that a thin zirconium oxide (ZrO2) layer formed on top of the organic semiconductor by atomic layer deposition (ALD) in low temperature performs as an efficient electron injection/hole blocking layer in organic light emitting diodes with forward architecture. The improved device performance is attributed to enhanced current injection arising from excellent energy level alignment at the F8BT/ZrO2 interface.Figure optionsDownload as PowerPoint slideHighlights
► Atomic layer zirconium oxide deposited at low temperature.
► ZrO2 as electron injection layer.
► Energy level alignment.
► Efficient hole blocking at the F8BT/ZrO2 interface.
► Improved outcoupling efficiency.