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Effect of Oxygen Plasma Surface Treatment on ITO Films Improving the Electrical Properties of ITO Films

Keywords:

films,the,of,ito,and,surface,to,treatment,plasma,is

Published on:

27 Apr,2021

Effect of Oxygen Plasma Surface Treatment on ITO Films Improving the Electrical Properties of ITO Films

Effect of Oxygen Plasma Surface Treatment on ITO Thin Films

As an important transparent semiconductor material, indium tin oxide (ITO) has not only stable chemical properties, but also excellent light transmittance and electrical conductivity, so it has been widely used in the optoelectronics industry. The conduction band of ITO is mainly composed of In and 5S orbital of Sn, while the valence band is dominated by 2p orbital of oxygen. The oxygen vacancy and Sn-substituted doped atoms constitute the donor level and affect the carrier concentration In the conduction band. The highly degenerate N-type semiconductor of ITO is formed due to the generation of oxygen vacancy and Sn-doped substitution In the film during deposition. Its Fermi level, Er, is above EC at the bottom of the conduction band, thus having a high carrier concentration and a low resistivity.

Oxygen plasma surface treatment

Effect of oxygen plasma surface treatment on ITO films

In addition, ITO has a wide optical band gap, so it has a high transmittance to both visible and near-infrared light. Due to the above unique properties, ITO thin films are widely used in photovoltaic batteries, electroluminescence, liquid crystal display, sensors, lasers and other optoelectronic devices. As is known to all, ITO belongs to non-stoichiometry, compounds, deposition conditions, post-treatment technology and cleaning methods and other factors will significantly affect its surface properties, especially the surface morphology and chemical composition of its surface, thus affecting the interface characteristics between ITO film and organic layer, and further affecting the optoelectronic performance of devices.

Therefore, before commercial ITO conductive glass is used to fabricate devices, it is usually necessary to adopt appropriate methods to treat the surface of ITO film, and improve the performance of devices by improving its surface electrical properties and surface morphology. Up to now, the methods used for surface modification of ITO can be divided into two types: dry treatment and wet treatment. Among them, the dry treatment of oxygen plasma surface treatment usually uses various ionized gas plasma to clean the surface of ITO to remove its surface pollution and improve its surface morphology. Wet treatment uses different organic solvents to bond new groups on the surface of ITO, so as to achieve the purpose of modifying its surface.

The surface of ITO anode was modified by oxygen plasma treatment. The changes of chemical composition, crystal structure, light transmittance and block resistance of ITO film before and after treatment showed that the surface of untreated ITO contained residual pollutants related to carbon element. After plasma treatment, the acromion strength of ITO was significantly reduced. This indicates that oxygen plasma surface treatment can effectively remove organic pollutants on ITO surface. Plasma treatment can not only reduce the carbon concentration on ITO surface, but also increase the oxygen concentration on ITO surface, and improve the chemical composition on ITO surface, which is very important for improving the work function of ITO and the performance of devices. In addition, a four-probe method was used to measure the block resistance of ITO samples before and after treatment. It is found that plasma treatment can reduce the block resistance of ITO electrode, which is beneficial to the improvement of device performance.

In conclusion, under the condition that the crystal structure and optical transmittance of ITO films are almost unchanged, oxygen plasma surface treatment not only reduces the block resistance of ITO, but also improves the chemical composition of ITO surface and the work function of ITO, thus optimizing the physical properties of ITO anode. Plasma surface modification is beneficial to improve the energy conversion efficiency of organic solar cells, improve the photovoltaic performance of the devices, and play an important role in improving the short circuit current, filling factor and energy conversion efficiency of organic solar cells.

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