ITO films have been in existence for more than 100 years, and their fields have gradually become wider and deeper with the passage of time. ITO films are highly favored by manufacturers in the photovoltaic industry due to their high transmittance and resistivity for solar cells. The Spectrophotometer and Four Point Probe Tester developed by Millennial Solar help companies control the production process and focus on improving the photoelectric conversion efficiency of commercial finished cells, thereby giving manufacturers a better product experience. In this issue of Millennial Solar, we will introduce to you what ITO film is and its characteristics and performance.

What is ITO film

ITO is an N-type oxide semiconductor - indium tin oxide, with tin and oxygen vacancies as donors. It has good electrical conductivity at room temperature. Its basic characteristics are absorption of ultraviolet rays and has little effect on visible light transmittance, which can better improve the performance of its products.

Characteristics of ITO film

ITO film has high electrical conductivity, high visible light transmittance, high mechanical hardness and good chemical stability. It is the most commonly used thin film material for solar cells. The ITO film has a complex cubic ferromanganite structure, and its main characteristics are:

1. Good electrical conductivity (resistivity can be as low as 10-4Ω·cm), wide band gap 3.5~4.3eV, high carrier concentration (1021cm-3) and electron mobility (15~45cm2/Vs-1) ;

2. The transmittance in the visible light band can reach more than 85%;

3. The absorption rate of ultraviolet rays is high, reaching more than 85%;

4. Reflective to infrared rays, with a reflectivity higher than 80%;

5. It has attenuation properties for microwaves, and the attenuation rate can reach more than 85%;

6. The film layer has high hardness, wear resistance and chemical corrosion resistance (except hydrofluoric acid, etc.);

7. The film layer has good acid etching and photolithography properties, facilitates fine processing, and can be etched into different patterns.

Basic properties of ITO films

The microstructure of ITO (In₂O₃:SnO₂=9:1), after Sn is infiltrated into In₂O₃, the Sn element can replace the In element in the In₂O₃ lattice and exist in the form of SnO₂, because the In element in In₂O₃ is the third order, forming SnO₂ At this time, an electron will be donated to the conduction band, and oxygen holes will be generated in a certain oxygen-deficient state, forming a carrier concentration of 1020 to 1021cm^-3 and a mobility of 10 to 30cm²/vs.

ITO resistance conversion chart

This mechanism provides a low film resistivity on the order of 10-4Ω.cm, so the ITO film has the conductive properties of a semiconductor. ITO is a wide-band thin film material with a band gap of 3.5-4.3ev. The excitation absorption threshold for the forbidden band in the ultraviolet region is 3.75ev, which is equivalent to a wavelength of 330nm. Therefore, the light transmittance of the ITO film in the ultraviolet region is extremely low. At the same time, the near-infrared region produces reflection due to the plasma vibration phenomenon of carriers, so the light transmittance of the ITO film in the near-infrared region is also very low, but the transmittance of the ITO film in the visible light region is very good. Due to the specific physical and chemical properties of the material itself, ITO films have good electrical conductivity and high light transmittance in the visible light region.

Four Point Probe Tester

E-mail: market@millennialsolar.com

Four Point Probe Tester is specially designed for scientific research. It can quickly and automatically scan samples up to 220mm, and obtain sheet resistance/resistivity distribution information at different locations of the sample. The dynamic test repeatability (close to the real scene) can reach 0.2%. The ultra-wide measurement range of 0.1mΩ~100MΩ can cover most application scenarios and can be widely used in many fields such as photovoltaics, semiconductors, alloys, and ceramics.

Spectrophotometer 

E-mail: market@millennialsolar.com

Spectrophotometer can be used to measure the transmittance, reflectance and absorbance of materials.

Spectrophotometer adopts a unique dual-beam optical design, which can perfectly correct the absorbance changes of different sample matrices, thereby stably measuring samples. It has the advantages of wide testing range, high precision and good stability. It also supports the measurement of solar transmittance in a wide range of wavelengths from the ultraviolet region to the near-infrared region, providing strong support for solar cell efficiency analysis.

The ITO film has the characteristics of low resistivity and high light transmittance, which can greatly improve the efficiency of solar cells. Millennial Solar focuses on improving the production quality of solar cells, solving the production quality control problems of solar photovoltaic cells from many aspects, and helping companies control the production process.