INFLUENCE OF DIFFERENT ANTI-REFLECTIVE LAYERS ON THE OPTICAL PROPERTIES OF SILICON-BASED SOLAR CELLS IN PVLIGHT HOUSE

ABSTRACT

In this paper, the effect of SiO₂, SiN_x, Al₂O₃ and TiO₂ light-reflecting layers with passivation properties on the properties of the solar cell is modeled in PV LIGHT HOUSE and the results obtained are theoretically analyzed. According to the results, for the anti-reflective layers SiO₂, SiN_x, Al₂O₃ and TiO₂, the maximum thickness at which the solar cell achieves the maximum absorption coefficient is 100 nm, 75 nm, 90 nm and 70 nm, respectively. This means that the optimal thickness of the anti-reflection layer is inversely proportional to the refractive index.

АННОТАЦИЯ

В данной работе в программе PV LIGHT HOUSE моделируется влияние светоотражающих слоев SiO₂, SiN_x, Al₂O₃ и TiO₂ с пассивирующими свойствами на свойства солнечного элемента и проводится теоретический анализ полученных результатов. Согласно результатам, для просветляющих слоев SiO₂, SiN_x, Al₂O₃ и TiO₂ максимальная толщина, при которой солнечный элемент достигает максимального коэффициента поглощения, составляет 100 нм, 75 нм, 90 нм и 70 нм соответственно. Это означает, что оптимальная толщина просветляющего слоя обратно пропорциональна показателю преломления.

Ключевые слова: солнечный элемент, просветляющий слой, моделирование, комплексный показатель преломления.

Keywords: solar cell, anti-reflection layer, modeling, complex refractive index

To reduce the reflection coefficient of the solar cell, a technology has been developed to cover the surface with anti-reflective coatings [1]. In the selection of anti-reflective layers, attention is paid to their refractive index and light absorption coefficient [2]. The refractive index of the anti-reflection layer should be in the range of the refractive index values ​​of air and silicon, and the light absorption coefficient should be close to zero. In addition, the anti-reflective layer on the silicon surface must be passive [3]. This is because the surface of silicon is an active area, and due to incomplete bonds and oxygen, this area has a high rate of recombination, which is called surface recombination. SiN_x [4], SiO₂ [5], [6] and Al₂O₃ [7] are mainly used to reduce surface recombination in silicon. Therefore, the back area of ​​the silicon-based solar cell is also covered with these substances. In this chapter, the optical properties of a single-crystal silicon-based solar cell coated with various anti-reflective layers are studied and analyzed. Figure 1 illustrates the dependence of the absorption, transition, and return coefficients of a 200 μm thick single-crystal silicon-based solar cell coated with SiN_x with a thickness of 100 nm (a) and 75 nm (b) on the wavelength of light. When SiN_x was 100 nm thick, the main absorption was in the range of 700–1000 nm of light wavelength, and at 75 nm, in the range of 500–800 nm of wavelength. The decrease in the thickness of SiN_x caused the absorption spectrum to shift from long wavelengths to short wavelengths. This is due to the formation of a useful internal interference. Therefore, the surface of a silicon-based solar cell is mainly coated with 75 nm thick SiN_x.

a                                                                b

Figure 1. Optical properties of a 200 μm thick single-crystal silicon-based solar cell coated with SiN_x with a thickness of 100 nm (a) and 75 nm (b)

In addition to SiN_x, SiO₂ is also used to cover the surface of solar cells with optical layers. Figure 2 illustrates the optical properties of a 200 μm thick single-crystal silicon-based solar cell coated with SiO2 with a thickness of 100 nm (a) and 75 nm (b).

a                                                                 b

Figure 2. Optical properties of a 200 μm thick single-crystal silicon-based solar cell coated with SiO₂ with a thickness of 100 nm (a) and 75 nm (b)

When a silicon-based solar cell is coated with 75 nm thick SiO₂, a decrease in the light absorption coefficient and an increase in the reflection coefficient are observed between 500-1000 nm of wavelength. When coated with 100 nm thick SiO₂, it was found that the light absorption coefficient remained almost high between these wavelengths. Therefore, for silicon-based solar cells, 100 nm thick SiO₂ is one of the optimal anti-reflective layers.

Mainly in industry, the surface of silicon-based solar cells is coated with SiN_x or SiO₂. However, in this dissertation, in addition to SiN_x and SiO₂, we also analyzed the optical properties of silicon-based solar cells coated with these substances, as Al₂O₃ has passivation properties and TiO₂ has an optimal refractive index for a silicon-based solar cell. Therefore, in Figure 3, the graphs of light wavelength dependence of the absorption, transition, and return coefficients of a 200 μm thick single-crystal silicon-based solar cell coated with Al₂O₃ (a) and TiO₂ (b) with a thickness of 100 nm described.

a                                                                 b

Figure 3. Optical properties of a 200 μm thick single-crystal silicon-based solar cell coated with Al₂O₃ (a) and TiO₂ (b) with a thickness of 100 nm

When the surface of a silicon-based solar cell was covered with a thickness of 100 nm, the light absorption coefficient was high and the reflection coefficient was low between 600-950 nm of wavelength. When coated with 100 nm thick TiO₂, a sharp decrease in the light absorption coefficient and a sharp increase in the refractive index in the range of 400-700 nm of wavelength, and an increase in the absorption coefficient and a decrease in the reflection coefficient in the range of 800-1000 nm. From all the graphs obtained above, it can be seen that the change in the thickness of the light-reflecting jumps mainly affects the light absorption and reflection coefficients of the solar cell. In general, the photogeneration coefficient was used to compare the absorption coefficients of light and to analyze the optical quality of the solar cell. The photogeneration coefficient is the ratio of the light energy used to generate an exciton, or pair of electrons, to the light energy incident on a solar cell. Therefore, the photogeneration coefficients of a silicon-based solar cell coated with two different light-reflecting layers at two different thicknesses of 75 nm and 100 nm are given in Table 1. At 75 nm thickness, SiN_x and TiO₂ achieved high photogeneration coefficients, while at 100 nm thickness, Al2O3 and SiO2 achieved high photogeneration coefficients. If we pay attention, the refractive index of SiNx and TiO2 is almost 2, and the refractive index of Al2O3 and SiO2 is close to 1.5. This means that the value of the optimal thickness of the anti-reflective layer covered by the surface of the solar cell is inversely proportional to the refractive index of this optical layer.

Table 1 .

Photogeneration coefficient of silicon-based solar elemenite coated with anti-reflective layers of different thicknesses

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