Superhydrophobic: Self-cleaning Photovoltaic Cells
A team of scientists at the Georgia Institute of Technology has developed a new treatment for silicon photovoltaic solar cells. This new method generates bumps and peaks on the surface that increase cell efficiency in two ways. The uneven surface protects the cells from water and dust. When water falls on the surface, it flows off taking away dust and dirt. This auto-cleaning mechanism will help the solar cells to absorb maximum sunlight most of the time. We all know that the three-dimensional structures manage to trap more light and reflect less. If the efforts of researchers of the Georgia Institute of Technology succeed, that will increase the light absorption, reduce reflection and keep cells neat and clean of dirt particles.
All this exercise will increase the cell efficiency up to 2%.
Dennis Hess, who is a professor in the Georgia Tech School of Chemical and Biomolecular Engineering, explains, “A normal silicon surface reflects a lot of the light that comes in, but by doing this texturing, the reflection is reduced to less than five percent. As much as 10 percent of the light that hits the cells is scattered because of dust and dirt of the surface. If you can keep the cells clean, in principle you can increase the efficiency. Even if you only improve this by a few percent, that could make a big difference.”
How was this team successful in creating peaks and valleys like situation on the surface? This team has tried etching the silicon with potassium hydroxide. The resulting reaction helps in removing some silicon and creates micron-scale pyramid like structures. They then resort to using an “e-beam process.” Through this “e-beam process” they put nanometre-scale gold particles to the pyramid structure. These gold particles behave as a catalyst when hydrogen fluoride and hydrogen peroxide are added to the mix. This process develops a second layer of structures and the much desired “superhydrophobic” characteristics.
The research team includes Yonghao Xiu, Shu Zhang. Yan Liu, is working with Georgia Tech’s University Center of Excellence for Photovoltaics Research and Education. This is headed by Professor Ajeet Rohatgi of Georgia Tech’s School of Electrical and Computer Engineering. This team will evaluate the surface treatment with real solar cells. But the point of caution is that successful implementation of the superhydrophobic surface treatment will eventually depend on its long-term robustness and cost.
Before commercializing the technology, the research team has to cross few hurdles. One of them is fragility of nano-scale structures. These structures are prone to damage and destruction. According to Hess, “Because the structures are so small, they are fairly fragile. Mechanical abrasion on the surface can destroy the superhydrophobicity. We have tried to address that here by creating a large superhydrophobic surface area so that small amounts of damage won’t affect the overall surface.”