Silicon solar cells use earth abundant raw materials and perform with high efficiency. They can only be installed in a limited number of places because they are based on thick, rigid and heavy wafers. Thin membranes are one of the ways to overcome this disadvantage. It will make the cells flexible and lightweight by reducing the amount of Si. These cells can be easily integrated into buildings, urban architecture and even small everyday gadgets. Light can't be absorbed by thin Si membranes. You can see through the 25% of the sunlight that is absorbed.
A group of researchers from AMOLF, Imperial College, and the University of Surrey have found a way to make thin photovoltaic cells opaque. In the lab, they found that the textured thin membranes absorb 65% of sunlight, which is very close to the theoretical absorption limit. It is likely that flexible, light-weight and efficient Si photovoltaic cells will be developed in the near future because of the highest light absorption ever demonstrated in a thin Si membrane.
How does it work?
The sunlight is re-directions into a range of angles by the patterned structure. The light has more chances to be absorbed with the light being trapped.
By knowing which light angles will trap the photon inside the Si, the researchers are able to design a pattern based on nature's order of the universe. Hyperuniform distributions and patterns are random, but there is some order. Hyperuniform designs combine the best of both worlds.
A whole family of hyperuniform pattern designs that all offer high design flexibility without compromising the optical performance has been demonstrated by the researchers. This is important for the implementation point of view, as not all designs can be easily fabricated in aScalable manner.
There are challenges.
The broad range of colors in the solar spectrum and the limited dimensions of the membrane are two key challenges in trapping sunlight in thin Si. Light guiding and trapping a single color is relatively simple and can be done efficiently using periodic structures. There are many colors in the sun, each of which has a different absorption power.
The problem was solved by roughening the surface with pyramidal features of dimensions similar to the wavelength of light. The same approach will not work in thin membranes with a thickness of the wavelength of light. The research team was able to circumvent this by patterning only a small portion of the cell's surface. It is not just applicable to thin Si, but also to any other light absorber thin film that needs extra help to absorb light.
There is an application.
Esther Alarcon Llado says that based on the strong light trapping performance of our patterns, we estimate that photovoltaic efficiency above 20% could be achieved for a 1 BC thick c-Si cell. Thinner Si absorbers are more tolerant to electronic defects. This means that thin Si cells with high efficiency could also be made from lower grade Silicon, thereby reducing the energy needs for raw Si purification and reducing their energy pay-back time.
Hyperuniform patterned thin photovoltaic is a promising technology. While there is still a lot of work to be done to make such thin high efficiency cells part of our living environment, this work makes us very optimistic that this will happen soon.
More information: Nasim Tavakoli et al, Over 65% Sunlight Absorption in a 1 μm Si Slab with Hyperuniform Texture, ACS Photonics (2022). DOI: 10.1021/acsphotonics.1c01668 Journal information: ACS Photonics Citation: Record efficiencies in thin film photovoltaic cells (2022, March 28) retrieved 28 March 2022 from https://phys.org/news/2022-03-efficiencies-thin-photovoltaic-cells.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
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