Effect of anti-reflective coating on solar cell performance

Photovoltaic power generation is an effect that converts solar energy into electrical energy. The reflectivity of the surface of solar cells without anti-reflection coating is very high. More than 30% of the incident light will be reflected from the silicon surface. Therefore, the main challenge facing the performance of solar cells is reflection loss. Light capture, surface texture and anti-reflection coating are the most widely used methods to reduce reflection loss. The Mei Neng velvet reflectometer is a powerful tool for solar cell manufacturers to detect reflectivity. It can test the reflectivity intensity of the cell to light of different wavelengths. The diffraction grating spectrometer is used to disperse the grating, and the resolution is higher.

Anti-reflection coating theory

Anti-reflection coating (ARC) plays a vital role in solar cells. Its main purpose is to reduce the reflection of light on the surface, thereby increasing the transmittance of light and improving the photoelectric conversion efficiency. Most solar cells are coated with anti-reflection coating. A well-optimized front surface anti-reflection coating can reduce the reflectivity of the front surface of the cell from 30% to less than 5%.

The above figure shows the principle of "light interference in thin films" (based on the interference phenomenon that occurs when light waves are reflected and transmitted between different medium interfaces). The light reflected from interfaces a and b interferes destructively, thereby transferring its energy to the cell. When the incident light is normally irradiated on the silicon surface covered with a transparent layer of thickness d1, the expression of the reflected energy is:

For a transparent layer with zero reflectivity:

In order to improve the performance of solar cells, it is necessary to consider the distribution of the solar spectrum and the relative spectral response of silicon and select a reasonable wavelength. The energy peak in the solar spectrum appears at 0.5μm, while the relative spectral response peak of the silicon cell is in the wavelength range of 0.8-0.9μm, so the wavelength range with the best anti-reflection effect is 0.5-0.7μm.

The reflectivity changes with wavelength, and the reflectivity curve of DLARC is W-shaped, which means that the reflectivity reaches the minimum value when corresponding to two wavelengths, and can reduce the reflectivity in a wide wavelength range (400-1200nm). It can be clearly seen from the figure that the effect of DLARC is much better than that of SLARC. In the wavelength range of 450-900nm, the reflectivity of DLARC of MgF₂/ZnS and SiO₂/TiO₂ is almost negligible.

The performance of solar cells with anti-reflection coatings was evaluated, including parameters such as short-circuit current (Isc), open-circuit voltage (Voe), fill factor (FF) and efficiency (η).

The efficiency of silicon solar cells without anti-reflection coatings was 9.3%, while the efficiency of single-layer anti-reflection coatings of Si₃N₄ was 13.6%. For double-layer anti-reflection coatings of MgF₂/ZnS and SiO₂/TiO₂, the efficiency of solar cells reached 14.28% and 14.34%, respectively.

For MgF₂/ZnS and SiO₂/TiO₂ in double-layer anti-reflection coatings, the internal quantum efficiency was >95% in the wavelength range of 450-900nm, with an increase of about 52% in short-circuit current. The increase in internal quantum efficiency corresponds to an increase in short-circuit current, which indicates that DLARC helps to improve the efficiency of solar cells in utilizing photons, thereby improving the performance of the cells.

It can be seen that SLARC can partially improve the performance of solar cells, while a properly designed DLARC can improve the performance to a large extent. By applying SiO₂/TiO₂ DLARC, low reflectivity can be achieved, the short-circuit current increases from 2.18 to 3.32, and the photovoltaic efficiency is about 14.34%.

Reflective coatings can reduce the reflectivity of silicon solar cells, thereby increasing photon absorption, improving short-circuit current and efficiency. The MeiNeng suede reflectometer is a powerful tool for solar cell manufacturers to detect reflectivity. It can test the reflectivity intensity of the cell to light of different wavelengths. The test results will be calculated by the software to calculate the photoelectric signal and finally presented as a visual curve, which is conducive to users to systematically characterize the reflectivity of the cell.