Scientists at the National Renewable Energy Laboratory (NREL) have discovered the structure of a single chemical that has been used for over 30 years to boost the performance of cadmium telluride (CdTe) solar cells. The findings could lead to improvements in the fabrication of a wide range of materials that use thin-film interfaces, including catalytic materials, microelectronics, electrochemistry, and detector materials.
CdTe solar cells are the second-most common photovoltaic technology after silicon solar cells, representing approximately one-third of the US utility-scale solar market in 2022. These cells rely on a thin film of material to absorb light and convert it into electricity. However, the electrical charges created by an absorbed photon can be trapped and lost at the interfaces between the light-absorbing layer and the layers that carry those charges away into electrical circuits. As early as the 1980s, researchers discovered that treating these interfaces with a small amount of cadmium chloride (CdCl2) could reduce the loss of charges and improve the cells’ power conversion efficiency. However, the atomic-level structure of the CdCl2 interface was not understood, making it difficult to optimize the treatment.
To understand the atomic structure of the CdCl2 interface, the NREL researchers and colleagues at Khalifa University, Bowling Green State University, and First Solar used a structure prediction algorithm for interfaces. They generated initial random arrangements of atoms at the interface and then updated those arrangements many times, allowing them to relax to their most stable arrangement. They found that the CdCl2 that formed at the interface assumed a unique structure not found in larger crystals of the material. This interface-specific atomic structure explains how the CdCl2 treatment improves the performance of CdTe solar cells.
The team’s findings, published in Applied Physics Reviews, suggest that materials do something different when they exist as atomically thin layers on or between other materials than when they are in the bulk. The ultrathin interface layer allows a previously unknown form of the material to exist with unique properties, which could have implications for the fabrication of other materials that rely on thin-film interfaces. The team plans to continue studying how materials behave at interfaces and hopes to develop more intentionally designed materials with better performance. Such insights could open doors for utilizing a wider range of materials than previously thought practical.
In conclusion, the NREL researchers’ discovery of the structure of the CdCl2 interface in CdTe solar cells has the potential to improve the performance of these cells and to revolutionize the fabrication of other materials that use thin-film interfaces. The team’s findings highlight the importance of studying how materials behave at interfaces and offer insights into the potential for new discoveries in the field of materials science.