Researchers in the Air Force Research Laboratory are making strides in material development that may open up new possibilities for thin, wearable electronics and other vital power applications.
Photovoltaics, or solar cells, are a key component in next-generation power applications, but integrating them into Air Force systems has been difficult because the materials that are being used to make those cells are typically thick, opaque, rigid, and heavy. Attempts to make thinner, lighter, and flexible cells greatly reduced their efficiency, making them impractical for today's advanced technologies such as flexible electronics and wearable sensors.
To address this issue, first AFRL researchers needed to find an inherently flexible material that could harvest solar energy efficiently. Then they had to find a way to make solar cells thinner, but better able to convert the energy to electricity. Using an inexpensive material called inorganic-organic hybrid perovskite, the team was able to make thin, transparent cells. However, the thinning of this material presented its own challenges.
Dr. Santanu Bag, project scientist, explained the challenges of thinning the material while retaining as much efficiency as possible. "One of the main issues of creating thin layers of perovskite is the formation of surface defects in the form of pinholes," said Bag. "The pinholes generate a high frequency of shunting pathways that prevent the charge from traveling through the absorber layer. This condition results in even greater device inefficiency than is caused by the film thinness itself."
To solve this problem, the research team exposed the surface of the solar cell to thiourea, an organic compound that acts as a "molecular glue" and introduces favorable interactions on the surface of the light-absorbing layer of the cell. The result is a continuous pinhole-free thin perovskite film that is much more efficient at creating electric power.
According to Bag, this innovation could have far-reaching implications for Air Force integrated power applications. These materials are useful not only as solar absorbers in photovoltaic devices, but as semiconductors, a class of materials which are used in modern computing and lighting devices. Potential applications include photodetectors, field-effect transistors, and light-emitting diodes, to name only a few. Bag said new sensor and wearable electronic technologies and applications could also emerge as a result of this innovation.
A patent application for this invention has been filed jointly by Bag and Dr. Michael F. Durstock, AFRL group lead, with funding from the Air Force Office of Scientific Research.
Bag said the next steps for the team are to simplify and scale-up the process of growing the perovskite films by introducing additive manufacturing into the fabrication process. The current spin-coating process is labor intensive, slow, and costly. Additive manufacturing provides a faster and less-costly way of producing the solar cells.
Source and top image: Air Force Research Laboratory
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