Self-assembled monolayer-modified ITO for efficient organic light-emitting diodes: The impact of different self-assemble monolayers on interfacial and electroluminescent properties

Abstract

Abstract Assembling monolayers between ITO electrode and the overlying organic layers is an important way to obtain high-performance organic light-emitting diodes (OLEDs). Herein, self-assembling monolayers (SAMs) based on pentafluorobenzylphosphonic acid (F5BPA) and heneicosafluorododecylphosphonic acid (HF21DPA) were formed on ITO surfaces. The work function of ITO was elevated from 4.82 eV to 5.20 eV and 5.81 eV by introduction of F5BPA and HF21DPA, respectively, which could facilitate hole transport into the device, and therefore improve charge balance in OLEDs. In addition, the water contact angles of ITO also increased from 46.45° to 87.09° and 110.6°, respectively, which could contribute to better-matched interfacial surface energy, and prevent the interface incompatibility. The surface properties of ITO after modification were also studied by using X-ray photoelectron spectroscopy, atomic force microscope and UV–visible spectra measurements. Besides, compared with the OLEDs using bare ITO anodes, the SAM-modified devices showed improved brightness (29245.49 cd/m2), higher luminous efficiency (6.09 cd/A), and smaller turn-on voltage (2.8 V). This promising approach provides a simple route for the fabrication of highly efficient OLEDs.