Surface and interface analysis for copper phthalocyanine (CuPc) and indium-tin-oxide (ITO) using X-ray photoelectron spectroscopy (XPS)

Indium-tin-oxide (ITO) has been widely used as a hole injection electrode for organic light-emitting devices (OLEDs), but the work function of ITO film usually mismatches the highest occupied molecular orbital (HOMO) of the hole transport materials. Copper phthalocyanine (CuPc) has been used as a hole injection buffer to enhance the hole injection from ITO to hole transport layer (HTL). A thin CuPc layer was thermally evaporated onto ITO-coated glass substrate and the surface and interface electron states of the CuPc/ITO close contact were measured and analyzed by X-ray photoelectron spectroscopy (XPS) technology. Results show that, in the interface of CuPc and ITO film, the role of oxygen is very crucial, the oxygen in ITO film may diffuse into the organic semiconductor and cause the alteration of electron states in organic materials.