Jul 18 2019
Scientists have discovered a new category of 2D perovskite materials with edges that are conductive like metals and cores that are insulating.
Topographical view of the surface of the perovskite layer (l) and electrical current image of the same layer showing the conductive edges (r). (Image credit: Penn State)
According to the researchers, these distinctive properties could find applications in nanoelectronics and solar cells.
This observation of the metal-like conductive states at the layer edges of these 2D perovskite materials provides a new way to improve the performance of next-generation optoelectronics and develop innovative nanoelectronics.
Kai Wang, Assistant Research Professor, Materials Science and Engineering, Penn State
Wang, the lead author of the study, and a group of Penn State scientists made the discovery while producing lead halide perovskite materials for use in next-generation solar cells. Perovskites are materials with a crystal structure superior in absorbing visible light and are an area of interest in creating rigid as well as flexible solar cells that can be commercial contenders of conventional cells composed of silicon.
These 2D perovskite materials are more economical to produce when compared to silicon and have the ability to be equally efficient at absorbing sunlight.
The study outcomes, described in Science Advances, offer a new understanding of the charge and energy flow in perovskite materials, essential for the continued progress of the technology, the researchers stated.
I think the beauty of this work is that we found a material that has completely different properties along the edges compared to the core,” said. “It’s very unusual that the current can flow around the edges and not in the center of a material, and this has huge implications for the design of solar cell architectures.
Shashank Priya, Professor of Materials Science and Engineering and Associate Vice President for Research, Penn State
The 2D perovskite materials are composed of thin, alternately stacked inorganic and organic layers. The organic layers safeguard the inorganic layers of lead halide crystals from moisture that can disintegrate 3D versions of the material. This layered structure leads to a great change in conductivity along parallel and perpendicular directions.
Using mapping and scanning methods, the scientists discovered that sharp edges of the 2D single crystals showed unusually large free charge carrier density.
“This work reveals the distinct differences in optoelectronic properties between the crystal layer edge and the core region, which can give a hint toward answering other important questions raised in the field of optoelectronics about these 2D perovskite materials,” Wang stated.
Scientists stated that the discoveries could improve the performance of solar cells and LED technology by offering additional charge pathways within the devices. Moreover, the study outcomes pave the pathway for the improvement of ground-breaking one-dimensional electrical conduction in nanoelectronics.
“Across the length of these materials, you have a junction between metal and semiconductor, and there are a lot of hypothetical devices proposed based on that junction,” stated Priya.
Due to the strong current present at the edges, 2D perovskite crystals may also be an excellent candidate for a triboelectric nanogenerator, the scientists stated.
Nanogenerators convert motion into electric power, which could give rise to wearable technology that charges phones and other devices with the help of both light and mechanical energy and inputs.
Congcong Wu, associate research professor, and Dong Yang and Ke Wang, assistant research professors from Penn State also contributed to the study.
Funding for this study was offered by the Air Force Office of Scientific Research, the Office of Naval Research, and the Army Small Business Innovation Research program.