Study of indium tin oxide -4,4′-bis(4-dimethylaminostyryl) benzene interface: an X ray photoelectron spectroscopy investigation

Abstract

The electrode-organic material interfaces are expected to play a crucial role in the charge injection mechanism in organic light emitting diodes (OLEDs), and hence have a strong impact on the efficiency of the devices. Recently, several investigations have been carried out on the interface formed between indium tin oxide (ITO) and organic layers but the structure of the interfacial layer is still not well known and contradictory results have been found. In this work, we have studied the interface formed between ITO and 4,4′-bis(4-dimethylaminostyryl) benzene (DMASB), an organic electroluminescent material which is a good emitter containing amine groups. The ITO–DMASB interface was analysed by X ray photoelectron spectroscopy (XPS). Comparison of the spectra recorded in the interface with those obtained in bare ITO substrate and in bare organic thin films showed a decomposition of the top layer of ITO, resulting in a diffusion of indium into the organic film and in the formation of a complex in the interface. This resulted from an interaction between metal indium with carbon, oxygen and nitrogen of the organic material. The changes in the interface structure are related to the electrical characteristics of devices using ITO as an anode.