Indium tin oxide (ITO), as an important transparent semiconductor material, not only has stable chemical properties but also excellent transparency and conductivity, making it widely used in the optoelectronic industry. The conduction band of ITO is mainly composed of 5s orbitals of In and Sn, while the valence band is dominated by 2p orbitals of oxygen. Oxygen vacancies and Sn substituted doping atoms form the donor energy level and affect the carrier concentration in the conduction band. ITO forms a highly degenerate n-type semiconductor due to the generation of oxygen vacancies and Sn doping substitution in the thin film during the deposition process. Its Fermi level EF is located above the conduction band bottom EC, resulting in a high carrier concentration and low resistivity. In addition, ITO has a wide optical bandgap, so it has high transmittance for both visible and near-infrared light. Due to the unique properties mentioned above, ITO thin films are widely used in optoelectronic devices such as photovoltaic cells, electroluminescence, liquid crystal displays, sensors, and lasers.

For organic photovoltaic cells and organic light-emitting devices, their typical structure is a sandwich structure, where one or more layers of organic functional thin films are sandwiched between upper and lower electrodes. The anode mostly uses transparent ITO conductive glass, so the surface characteristics of ITO have a significant impact on device performance.

Experiments have found that oxygen plasma treatment on the surface of ITO can improve its work function, as the oxygen content on the surface of ITO substrates increases after peroxide plasma treatment, and a layer of negatively charged oxygen is enriched to form an interface dipole layer, resulting in an increase in work function. The increase of ITO interface work function can reduce the injection potential barrier of holes, which has a significant effect on improving device efficiency.

In addition to improving the work function of ITO electrodes, another important reason for plasma cleaning is that oxygen plasma treatment can increase the surface energy and polarity of ITO, improving its surface wettability. Polymers are organic materials with low surface energy and low polarity. On the one hand, increasing the surface energy and polarity of ITO electrodes is beneficial for improving the wettability of polymer solutions on ITO surfaces, resulting in better uniformity of polymer luminescent films prepared by spin coating, and greatly reducing the occurrence of "pinholes" caused by poor film uniformity; On the other hand, increasing the surface energy and polarity of the ITO electrode can increase the adhesion energy of the ITO electrode/organic layer interface, enhance the adhesion between the ITO electrode and the organic thin film layer, and form a more firmly attached, smoother, and gapless ITO electrode/organic layer interface. This can greatly increase the effective area of interface charge injection, improve the efficiency of interface charge injection, and thus help improve the energy conversion efficiency of organic solar cells and enhance the photovoltaic performance of devices.