Today, there is no cheaper way to generate electricity than by using the sun. Solar power plants are currently being constructed in sunny locations to provide solar electricity for less than two cents per kilowatt hour. Solar cells based on crystalline silicon are now available on the market, with efficiencies of up to 23%. As a result, they control approximately 95 percent of the global market. Costs could be reduced even further with even higher efficiencies of more than 26%.
An international working group led by photovoltaics researchers from Forschungszentrum Jülich intends to achieve this goal using a nanostructured, transparent material for the front of solar cells and a sophisticated design. In the scientific journal Nature Energy, the scientists report on the results of their many years of research.
Energy is critical for economic growth and development. With rapid development and a desire to expand the economy, society requires more electricity. Together with the recognition that unsustainable energy production can have a negative impact on our environment. Solar energy is the most abundant method of capturing energy in nature.
An international working group led by photovoltaics researchers from Forschungszentrum Jülich now plans to reach this goal with a nanostructured, transparent material for the front of solar cells and a sophisticated design.
Silicon solar cells have steadily improved over the last several decades and have now reached a very advanced stage of development. However, the disturbing effect of recombination persists after sunlight absorption and photovoltaic generation of electrical charge carriers. Negative and positive charge carriers that have already been generated combine and cancel each other out in this process before they can be used for the flow of solar electricity. This effect can be mitigated by using special materials with a unique property known as passivation.
“Our nanostructured layers provide exactly this desired passivation,” says Malte Köhler, a former Ph.D. student and first author at the Jülich Institute for Energy and Climate Research (IEK-5), who has since received his doctorate. Furthermore, the ultra-thin layers are transparent (light incidence is not reduced) and have a high electrical conductivity.
“No other approach has so far combined these three properties – passivation, transparency, and conductivity – as well as our new design,” says Dr. Kaining Ding, head of the Jülich working group. In the laboratory, the first prototype of the Jülich TPC solar cell achieved high efficiency of 23.99 percent (+- 0.29 percent). This value was also confirmed by the Institute for Solar Energy Research’s independent CalTeC laboratory in Hamelin (ISFH).
This means that the Jülich TPC solar cell is still slightly inferior to the best laboratory-made crystalline silicon cells to date. However, parallel simulations have revealed that TPC technology can achieve efficiencies of more than 26%.
“In addition,” Ding emphasizes the advantage over other research approaches, “we have only used manufacturing processes that can be integrated relatively quickly into series production.” The Jülich scientists’ strategy paves the way for their development from the laboratory to a large scale in industrial solar cell production with minimal effort.
To create the layers of the TPC solar cell, several process steps were required. The researchers deposited a double layer of tiny pyramid-shaped silicon carbide nanocrystals on a thin layer of silicon dioxide at two different temperatures. Finally, an indium tin oxide transparent layer was applied. Ding and colleagues employed wet chemical processes, chemical vapor deposition (CVD), and sputtering.
The Jülich researchers from IEK 5 and the Jülich Ernst Ruska Center for Electron Microscopy collaborated closely with institutes in the Netherlands, China, Russia, and Ecuador to achieve success. Researchers from RWTH Aachen University, the University of Duisburg-Essen, the Technical Universities of Delft and Eindhoven, the Universidad San Francisco de Quito, Novosibirsk University, and the Kutateladze Institute of Thermophysics, and Sun Yat-Sen University in Guangzhou are among the collaborators. Kaining Ding’s research team intends to improve the power yield of its TPC solar cells in the future. “We expect solar cell manufacturers to show great interest in our technology,” Ding says.