Wednesday, 20 July 2016

How absorption coefficient determines which material is used to make solar cells?

How absorption coefficient determines which material is used to make solar cells?


Does the knowledge of the material absorption coefficients aids engineers in determining which material to use in their solar cell designs? If yes, how?






The solar spectrum hitting the earth corresponds to black body radiation (apart from some absorption lines due to gasses in our atmosphere and inherent to the sun). In principle, one wants to harvest an as large as possible fraction of this spectrum.
Solar cells can be optimized by increasing the absorption at a certain wavelength (which mostly depends on the bandgap of the semiconductor material used). On the other hand, they can also be optimized by joining several layers, which convert different wavelengths into an electrical voltage. I admit that multi-junction solar cells are more at a research stage at the moment, but they present an interesting approach.
Another problem, which is somewhat related is the incoupling efficiency. A significant part of the incident light is reflected and never makes it into the active material. Therefore one has to engineer anti-reflection layers, which also need to be optimized to be either broadband or work for certain wavelength ranges. In the simplest case this can be done by roughening the surface of silicon chips by etching them with KOH.



need to try etching.....with acid or base

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