Caption: Researchers propose an innovative design for 2D TMDC solar cells that could significantly increase their efficiency. [Image credit: ESA – P. Carril]
Researchers at the University of Pennsylvania have put forth a novel design for lightweight 2D transition metal dichalcogenide (2D TMDC) solar cells, aiming to enhance their efficiency from the current 5% to an impressive 12%. These solar cells, known for their high specific power, which is crucial for space exploration and settlements, have been improved through the integration of a superlattice structure, resulting in amplified solar absorption. The next stage of development involves establishing a method for large-scale production.
In the realm of energy supply for space exploration and settlements, conventional silicon or gallium arsenide solar cells remain excessively heavy for practical rocket transportation. As a solution, researchers are actively exploring lightweight alternatives, including solar cells made from a thin layer of molybdenum selenide, which falls under the broader category of 2D TMDC solar cells. In a publication in the inaugural issue of the journal Device on June 6, researchers propose a device design that can elevate the efficiencies of 2D TMDC solar cells from the existing 5% to an impressive 12%.
According to Deep Jariwala, the lead author and member of Device’s advisory board at the University of Pennsylvania, “I think people are slowly coming to the realization that 2D TMDCs are excellent photovoltaic materials, though not for terrestrial applications but for applications that are mobile—more flexible, like space-based applications. The weight of 2D TMDC solar cells is 100 times less than silicon or gallium arsenide solar cells, so suddenly these cells become a very appealing technology.”
While 2D TMDC solar cells are not as efficient as silicon solar cells, they possess a higher electricity generation capability per unit weight, known as “specific power.” This advantage stems from their incredibly thin nature, with a layer that is only 3-5 nanometers thick, which is over a thousand times thinner than a human hair, effectively absorbing sunlight comparable to commercially available solar cells. The label “2D” is attributed to their extreme thinness, as they consist of just a few atoms in thickness.
Jariwala explains, “High specific power is actually one of the greatest goals of any space-based light harvesting or energy harvesting technology. This is not just important for satellites or space stations but also if you want real utility-scaled solar power in space.”
The transportation of a sufficient number of solar cells required for space applications is currently impractical due to the large volume, making it economically unviable. Thus, a solution involves the utilization of lighter weight cells with enhanced specific power.
Although the full potential of 2D TMDC solar cells is yet to be realized, Jariwala and his team aim to further improve their efficiency. Typically, the performance of these solar cells is optimized through the fabrication of a series of test devices. However, Jariwala’s team believes that computational modeling is equally crucial in achieving this goal.
Furthermore, the team emphasizes the importance of accurately considering one of the device’s defining features—excitons—which pose a challenge to model. Excitons are generated when the solar cell absorbs sunlight, and their presence significantly contributes to the high solar absorption of 2D TMDC solar cells. The separation of the positively and negatively charged components of an exciton leads to the production of electricity within the solar cell.
By employing this modeling approach, the team has devised a design that exhibits double the efficiency compared to the previous experimental demonstration.
Jariwala elaborates, “The unique part about this device is its superlattice structure, which essentially means there are alternating layers of 2D TMDC separated by a spacer or non-semiconductor layer. Spacing out the layers allows you to bounce light many, many times within the cell structure, even when the cell structure is extremely thin.”
“We were not expecting cells that are so thin to reach a 12% efficiency. Given that the current efficiencies are less than 5%, my hope is that in the next 4 to 5 years, people can actually demonstrate cells that are 10% and higher in efficiency.”
The next phase of the research involves devising methods to achieve large-scale production of the proposed design. Jariwala explains, “Right now, we are assembling these superlattices by transferring individual materials one on top of the other, like sheets of paper. It’s as if you’re tearing them off from one book, and then pasting them together like a stack of sticky notes. We need a way to grow these materials directly one on top of the other.”
Reference: “How Good Can 2D Excitonic Solar Cells Be?” by Device, Hu et al., 6 June 2023, Device.
DOI: 10.1016/j.device.2023.100003
This work was supported by the Asian Office of Aerospace Research and Development (AOARD), the Air Force Office of Scientific Research (AFOSR), the Office of Naval Research, University Research Foundation at Penn, the Alfred P. Sloan Foundation, and the Center for Undergraduate Research Fellowships (CURF) at U. Penn.
[Note: The consent statement at the end of the original text has been removed for clarity.]
