Conventional energy sources (petroleum, coal, natural gases, etc) are limited in supply and cause excessive pollution, and so, renewable energy is becoming an increasingly important energy source. Yet, renewables need to overcome a few issues in order to replace the fossil fuels. This challenges researchers to find a solution that will be more accessible for mass production, cheaper and more efficient. The researchers from the University of Groningen found an interesting solution that can significantly improve solar cell efficiency. The results were recently published in Nature Communications.
The research team noticed that energy was lost very quickly when photons with energy higher than the band gap of the semiconductor were absorbed by the solar cell. The issue here is that energy was dissipated as heat and did not contribute to an increase in voltage. This process creates high-energy electrons known as “hot electrons.” Releasing an excess energy, hot electrons cause vibrations in crystalline silicon and thus limit the efficiency of the solar cells.
With these findings, the researchers made solar cells by using a material in which hot electrons can retain high energy levels for a long time. This means that the cells can take more of the energy and generate a higher voltage. These cells are made of organic-inorganic hybrid perovskites. Perovskites are a calcium titanium oxide mineral that has a crystal structure. Many different cations can be embedded in its structure allowing the development of different materials. The biggest disadvantage of a hybrid-perovskite solar panel is the use of a toxic lead.
The researchers have found that using the harmless tin instead of lead can increase solar cells efficiency by 9 percent. In this case, hot electrons with high energy levels are retained in cells a thousand times longer than in the case of commonly used silicon-based cells (several nanoseconds instead of hundred femtoseconds). The extended hot electrons duration gives sufficient time, allowing solar cells to absorb their energy before it is dissipated as heat. The calculations have shown that hybrid-perovskite solar cells could improve the efficiency from 33 percent to 66 percent.
The next challenge for the researchers is to figure out why the tin-based hybrid perovskite slows down energy dissipating of hot electrons. By solving this, they could make modifications on the material resulting in an even slower process and additionally increased efficiency.
The tin-based hybrid perovskite solar cells have the potential to overcome the current disadvantages of solar energy and provide a clean, sustainable and cost-effective energy solution.