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ZnO

Improving the efficiency and lowering the environmental impact of solar cells

An article published by Professor of Physics Parameswar Hari and his former graduate student Amrit Kaphle (PhD ’19) has been selected for the RSC Advances 10th-anniversary collection focused on solar energy. At the same time, another of Hari’s peer-reviewed papers, written with his current doctoral student Rusiri Rathnasekara, has received the distinction of being featured on the cover of the May 2021 issue of Journal of Materials Research.

black and white electron microscope image of nanoribbons
Scanning electron microscope (SEM) image of nanoribbons

These publications are the results of work Hari and his co-investigators have been conducting for nearly eight years. Their endeavors are aimed at addressing two of the major drawbacks of solar cells. First, such cells are composed of 95% silicon, which is fabricated using a high-energy process that has a heavy carbon footprint. Second, the best silicon solar cells are only 24% efficient. In order to promote the widespread use of solar technology, Hari explained, two things must happen: the cost of production must decrease significantly and the method of manufacturing must be carbon neutral.

High-efficiency solar cells: cost effective and carbon neutral

To achieve these goals, said Hari, “the focus of our investigations has been on fabricating high-efficiency solar cells using novel materials that are both abundant in nature and cost effective.” One such material Hari and his co-investigators have explored and tested is nano-structured zinc oxide (ZnO). Specifically, they have been analyzing mechanisms for controlling the efficiency of thin-film ZnO suitable for solar cell applications.

black and white image of cross-sectional view of nanorods
Scanning electron microscope (SEM) image of nanorods (cross-sectional view)

In the RSC Advances article — Enhancement in the performance of nanostructured CuO-ZnO solar cells by band alignment – Hari and his team reported on their discovery that by carefully “doping” ZnO with cobalt, the light absorption in thin-film zinc oxide could be improved. “This will ultimately enhance the efficiency of solar cells made of this material,” Hari noted.

The researchers’ contribution to the Journal of Materials ResearchImpedance spectroscopy of nanostructured ZnO morphologies – documents the testing of a new electrode made of the thin-film material in a dye-sensitized solar cell. Using impedance spectroscopy in the Oklahoma Photovoltaic Research Institute lab at The University of Tulsa, Hari and Rathnasekara found a significant improvement in the performance of this solar cell.

As the world shifts away from fossil fuels and interest grows in solar energy and other renewable resources, Hari and his colleagues’ research becomes ever more important. Added to that, Hari noted, the U.S. military has become interested in the ability of cost-effective thin-film solar cells to replace expensive solar cells currently used in drones and other aircraft.


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