The Electronic Band Structure Evaluation of OLED Materials by Combination of LEIPS and UPS

Abstract

The electron affinity and ionization potential of OLED materials were evaluated using low energy inverse photoelectron spectroscopy (LEIPS) and ultraviolet photoelectron spectroscopy (UPS), which can be incorporated into a multi-technique X-ray Photoelectron Spectroscopy (XPS) system. The energy level of lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) were estimated by LEIPS and UPS for three kinds of samples, i.e. CuPc (Cu phthalocyanine) thin film (10 nm) / ITO (indium tin oxide) film / glass substrate, C₆₀ thin film (10 nm) / Au film / ITO film / glass substrate, and α-NPD (Bis[N-(1-naphthyl)-N-phenyl]benzidine) thin film (10 nm) / ITO film / glass substrate, respectively. The band gap at the surface of the materials were determined by these levels. In addition, by utilizing Ar-gas cluster ion beam (Ar-GCIB), in-situ LEIPS and UPS depth profiling of interface of the multilayer films were also demonstrated.