TCO films include In₂O₃ series and ZnO series. In heterojunction solar cells, the commonly used TCO material is tin-doped In₂O₃, that is, ito, which has both transparency and conductivity. Millennial Spectrophotometer UVN2800 can measure the reflectance and transmittance of thin film materials such as ito and amorphous silicon, and is widely used in the photovoltaic industry.

ITO Thin Film

According to the manufacturing process of a-Si:H/c-Si heterojunction solar cells, after the emitter and BSF are deposited, an ito film needs to be formed on the front and back of the cell. This is because a-Si:H/c-Si heterojunction solar cells, compared with traditional heat-diffusing crystalline silicon solar cells, have low conductivity of the emitter, so that it can only collect current from the emitter through metal grid lines. , which is not enough, so it is necessary to use a conductive and transparent film to transport charges.

In order to obtain an efficient SHJ cell, VOC, Jsc, and FF, the three basic parameters that characterize the cell, must be simultaneously improved. From the perspective of ITO thin films, the basic parameters of the cell can be improved from the following three perspectives:

■ Low damage deposited ITO film can improve Voc;

■ Jsc can be improved by using ITO film with high electron mobility;

■ Reducing the sheet resistance of ITO is beneficial to obtain high FF.

Commonly used ITO materials include SnO₂ system, In₂O₃ system and ZnO system. Fluorine-doped SnO2 is mainly deposited on large-area float glass and is often used in thin-film solar cells. It is incompatible with the process of silicon-based heterojunction solar cells, so it will not be discussed here.

Tin-doped In₂O₃ is the most commonly used ITO material, which is widely used in the production of flat panel displays and is also the main ITO material used in HJT cells. The application of ito thin film in HJT cell plays three roles.

■ Allow as much light as possible to pass through the ITO and enter the emitter and base regions.

■ The refractive index of ITO is close to that of SiNx film, so it can be used as anti-reflection layer at the same time.

■ ITO satisfies the requirement of conduction in electricity.

However, the optical properties and electrical properties of ITO thin films are interdependent and cannot be optimized independently. A balance must be found between the two.

Millennial Spectrophotometer

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Millennial Spectrophotometer can be used to measure material transmittance, reflectance and absorbance.

Millennial Spectrophotometer The unique double-beam optical design can perfectly correct the absorbance changes of different sample matrices, so that the samples can be measured stably. It has the advantages of wide testing range, high precision and good stability. And it supports the measurement of solar transmittance in a wide range of wavelength regions from the ultraviolet region to the near infrared region, providing strong support for the efficiency analysis of solar cells.

On the whole, the ITO film has both conductivity and transparency, which greatly improves its application in the photovoltaic field, and improves the performance of silicon heterojunction solar cells, which plays a pivotal role in silicon heterojunction solar cells ; Millennial Spectrophotometer can measure the reflectance and transmittance of ITO thin films, and continuously promote the innovation and development of photovoltaic industry technology.