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Nano-Abrasive Material Makes Self-Cleaning Solar Cells


13035_webOne of the most important steps in designing a new solar cell is taking into account its reflective properties, and make reflection as low as possible, for most of the light to impress the photosensitive area.

Scientists from GIT (Georgia Institute of Technology) have invented a new solar cell surface treatment that could be applied to existing solar cells technology, and that could boost the light absorption into the cell. It also has self-cleaning capabilities.

The method of abrasion is chemical at its roots, and it uses two types of etching to create porous surfaces at both the micron and nanometer size scales. “The more sunlight that goes into the photovoltaic cells and the less that reflects back, the higher the efficiency can be,” said C.P. Wong, Regents’ professor in Georgia Tech’s School of Materials Science and Engineering. “Our simulations show that we can potentially increase the final efficiency of the cells by as much as two percent with this surface structure.”

Interestingly, the micronic abrasion isn’t just going to trap the light inside the cell’s surface, but it is also going to repel water droplets and dust along with them, and become self-cleaning, by mimicking the way lotus leaves function. This property of the newly-created surface is called “superhydrophoby”, and it uses surface roughness at two different size scales to create high contact angles, repeling water from rain or condensation. “When a water droplet reaches the surface, it sits on top of this two-tier roughness and only about three percent of it is in contact with the silicon,” the professor said.

Preparation of the superhydrophobic surface begins with use of a potassium hydroxide (KOH) solution to etch the silicon surface. The solution preferentially removes silicon along crystalline planes, creating micron-scale pyramid structures in the surface.

An e-beam process is then used to apply nanometer-scale gold particles to the pyramid structures. Using a solution of hydrogen fluoride (HF) and hydrogen peroxide (H2O2), a metal-assisted etching process – with gold as the catalyst – produces the nanometer-scale features. The feature size is controlled by the diameter of the gold particles and the length of time the silicon is exposed to the etching.

Finally, the gold is removed with a potassium iodide (KI) solution and the surface coated with a fluorocarbon material, perfluorooctyl tricholosilane (PFOS).

The researchers also say that their manufacturing process isn’t going to increase solar cell production costs by much, being able to adapt itself to the existing fabrication technology.

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