New '2D' solar cell design could revolutionize space exploration

“I think people slowly realize that 2D TMDCs are excellent photovoltaic materials, though not for terrestrial applications, but for applications that are mobile—more flexible, like spacebased applications,” says lead author and Device advisory board member Deep Jariwala of the University of Pennsylvania. “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,” he added.

2D TMDC solar cells' extreme thinness earns them the label of “2D”—they are considered “flat” because they are only a few atoms thick. “High specific power is one of the greatest goals of any space-based light harvesting or energy harvesting technology,” says Jariwala.

“This is not just important for satellites or space stations but also if you want real utility-scaled solar power in space,” he added. "The number of solar cells you would have to ship up is so large that no space vehicles currently can take those kinds of materials up there in an economically viable way. So, the solution is double up on lighter-weight cells, which give you much more specific power,” Jariwala explained.

Jariwala and his team are working further to enhance the efficiency of 2D TMDC solar cells, as their full potential has yet to be fully realized by focusing on something called "excitons." These are produced when the solar cell absorbs sunlight, and their dominant presence is why a 2D TMDC solar cell has such high solar absorption. Electricity is produced by the solar cell when an exciton's positively and negatively charged components are funneled off to separate electrodes.

“The unique part about this device is its superlattice structure, which essentially means a spacer or non-semiconductor layer separates alternating layers of 2D TMDC,” says Jariwala. “Spacing out the layers allows you to bounce light many, many times within the cell structure, even when the cell structure is extremely thin,” he added.

“We were not expecting cells so thin to see a 12 percent value. Given that the current efficiencies are less than 5 percent, I hope that in the next 4 to 5 years, people can demonstrate cells that are 10 percent and upwards in efficiency,” Jariwala added.

You can review the study for yourself in the journal Device.

Study abstract:

"Excitonic semiconductors have been a subject of research for photovoltaic applications for many decades. While organic photovoltaics have now exceeded 19% power conversion efficiency (PCE), the advent of inorganic semiconductors such as two-dimensional transition metal dichalcogenides (TMDCs) has renewed interest in excitonic solar cells due to their sub-nm film thicknesses. While several reports have been published on TMDC-based photovoltaics, achieving PCEs higher than 6% has remained challenging. In this study, we perform a comprehensive analysis of the optical and electronic characteristics of TMDC-based excitonic PV devices. Our designs are consciously chosen with the consideration of manufacturing challenges associated with large-area photovoltaic technologies. Our analysis suggests that whereas the PCE for 2D excitonic solar cells may be limited to <13%, a specific power >100 W g1may be achieved with our proposed designs, making them attractive in aerospace applications, distributed remote sensing, and wearable electronics"