4.3 Conventional approaches used to boost the efficiency in crystalline silicon solar PV industry
4.3 Conventional approaches used to boost the efficiency in crystalline silicon solar PV industry
A solar cell is a sustainable factory built to produce solar electricity. It relies on nothing but sunlight which is one and only raw material it needed to generate electricity!
Just like any other factory does, solar cells need more raw material in order to produce more. The greater the solar intensity received the greater the solar power they generate. Traditionally, three different strategies are employed to raise the number of light photons that participate in the generation of electricity: Anti-reflective coatings, textured front-sides, and metallic back reflectors. They are all straightforward concepts. But their individual contribution in the operation cannot be underestimated at all. Let us see: Why?
Anti-reflective coating
Bare crystalline silicon solar cells reflect a substantial portion of incoming sunlight since pure crystalline silicon is highly shimmering. This results in low photocurrent and low module efficiency. The degree of reflectance may vary with the wavelength. This reflective effect reduces the number of light photons going through the front side on to the cell. On average, as much as 30% of IR and 50% of the UV portion is lost due to the reflection [1].
Is it possible to reduce the reflective loss to improve the light absorption capacity and efficiency of photovoltaics?
Yes! This is how the idea of an anti-reflective coating was born.
Reducing the reflection means increasing the number of photons transmitting on to the cell and increasing the overall efficiency. This is done by applying an anti-reflective coating. While various systems such as SiO2, TiO2, Al2O3, ZnO, ZnS, and Si3N4 have been proven to be anti-reflective, SiO2, Si3N4, and TiO2 are the most common materials being used in the industry [1, 2, 3].
Role of an anti-reflective coating
Without anti-reflective coatings, solar PVs would not be economically viable. Moreover, it has been demonstrated that the reflective loss can more efficiently be reduced by applying a double layer anti-reflective coating. An efficiency enhancement of 214% and 60% have been reported with a double layer anti-reflective coating (SiO2/ TiO2) and with a single layer SiO2 coating as compared to as-grown silicon solar cells [1]. As it can be seen, the role of an anti-reflective coating is crucial to manufacture crystalline silicon solar cells at a lower cost with higher efficiency.
In next articles, we will see the duty, and significance of a textured front-side, and metallic back reflector in improving the efficiency.
Reference
[1] Ali, K., Khan, S. A., & Jafri, M. M. (2014). Effect of double layer (SiO2/TiO2) anti-reflective coating on silicon solar cells. Int. J. Electrochem. Sci, 9, 7865-7874.
[2] Al-Turk, S. (2011). Analytic Optimization Modeling of Anti-Reflection Coatings for Solar Cells (Doctoral dissertation).
[3] Du, Q. G., Alagappan, G., Dai, H., Demir, H. V., Yu, H. Y., Sun, X. W., & Kam, C. H. (2012). UV-blocking ZnO nanostructure anti-reflective coatings. Optics Communications, 285(13-14), 3238-3241.