ANTI-REFLECTIVE PROPERTIES OF GRADIENT-POROUS SILICON

The theoretically achievable efficiency of the PEC for the single-cell solar cells (SC) is 30%. However, the cost of electricity generated by means of the solar cells has already become equal to that of natural gas. At the same time, the maximum confirmed efficiency for the solar cell is 26.3%. Thus, a certain lag behind the theoretically possible value is still observed. Analysis of the losses of modern photoelectric converters shows that at least 10% of them are related to the reflectivity of the SC surface. Therefore, along with intensive studies on heterojunction, thin-film constructive solutions, much attention is paid to other ones that allow for more than double the conversion efficiency. The paper deals with the formation of antireflective coatings on the surface of the PEC. One of the promising antireflection materials, which is widely studied at the present time, is porous silicon, called black silicon (black silicon b-Si) in the literature. The development of chemical and anodic silicon etching technologies, as well as the low cost and simplicity of the forming process, allow producing b-Si structures with controlled parameters of the antireflection layers. This paper presents the comparative results of the investigation of the reflection coefficients of various porous films obtained by anodic etching of the surface of silicon wafers with orientations (100) and (111). Experimental data indicate a significant decrease in the reflection coefficient in the visible light range from 400 to 1200 nm for all samples with porous layers compared to samples without porous layers. Especially noticeable is the decrease in the degree of reflection for the variational gradient-porous (GPSi-var) structures with a nano-porous outer layer. The magnitude of the reflection coefficient for such structures falls to the level of 0.1% in the range of the investigated frequencies of light radiation. For all porous layers, the tendency of decreasing the degree of reflection is typical as the wavelength of light decreases to less than 10% (compared to the reflection coefficient of the surface of silicon wafer at 30%).

reflection coefficient, porous silicon, anodic etching, black silicon, solar energy

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