Two-dimensional perovskite materials have unique conductive edge states

Researchers have discovered a new class of two-dimensional perovskite-based materials with conductive edges as well as insulating cores. These unique properties have applications in solar cells and nanoelectronics.

"This observation of metal-like conductive states at the edges of the layers of these 2D perovskite materials provides a new way to improve the performance of next-generation optoelectronics and to develop innovative nanoelectronics," said Kai Wang. , assistant professor of research in materials science. and engineering at Penn State and lead author of the study.

Wang and a team of Penn State researchers made this discovery by synthesizing lead-halide perovskite materials for use in next-generation solar cells. Perovskites, materials with a crystalline structure that can absorb visible light, are at the heart of the development of rigid and flexible solar cells capable of competing commercially with traditional silicon cells. The creation of two-dimensional perovskite materials is less expensive than silicon and has the potential to be equally effective at absorbing sunlight.

The results, reported in Progress of science, provide new information on the load and energy flow in perovskite-based materials, important for the continuous progress of the technology, said the scientists.

"I think the beauty of this work lies in the fact that we have found a material with completely different properties along the edges compared to the core," said Shashank Priya, Professor of Materials Science and Engineering. and Associate Vice President, Research at Penn State. "It is very unusual for the current to flow around the edges and not at the center of a material, which has enormous implications for the design of solar cell architectures."

The 2D perovskite materials consist of organic and inorganic thin layers stacked alternately. The organic layers protect the inorganic layers of lead halide crystals from moisture likely to degrade 3D versions of the material. This layered structure causes a large variation in the conductivity in perpendicular and parallel directions.

Using scanning and mapping techniques, the researchers found that the sharp edges of 2D single crystals exhibited an extraordinarily high free charge carrier density.

"This work reveals the distinct differences in optoelectronic properties between the edge of the crystal layer and the central region, which may give an indication to address other important issues raised in the field of optoelectronics. about these 2D-based perovskite materials, "Wang said.

The researchers said the results could improve the performance of solar cells and LED technology by providing additional charge paths in the devices. The results also pave the way for the development of innovative one-dimensional electrical conduction in nanoelectronics.

"Throughout the length of these materials, you have a junction between the metal and the semiconductor, and many hypothetical devices are proposed on the basis of this junction," said Priya.

Due to the strong current found around the edges, 2D perovskite crystals could also be a good candidate for a triboelectric nanogenerator, the researchers said.

Nanogenerators convert motion into electrical energy, which could result in portable technology that recharges phones and other devices using both light, mechanical energy and inputs.

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