Researchers devise Mie-resonant ETL for highly efficient perovskite solar cells

Researchers from Russia-based ITMO University and the University of Rome Tor Vergata have developed a paste made of titanium dioxide (TiO₂) and resonant silicon nanoparticles, claimed to improve light absorption in perovskite solar cells based on methylammonium lead iodide (MAPbI₃).

The scientists created a mesoporous electron transport layer based on optically resonant silicon nanoparticles which were then incorporated into TiO₂ paste. 'Such particles serve as nanoantennae ' they catch light and it resonates inside them. And the longer light stays in the photoactive layer, the more of it is absorbed by the material,' said Sergey Makarov, professor at ITMO's school of physics and engineering.

The silicon nanoparticles are Mie-resonant, meaning they can create magnetic or electric resonance based on displacement currents. 'Thanks to this effect, the nanoparticles can amplify various optical phenomena, including light absorption and spontaneous radiation. In other words, they do work as nanoantennae,' the researchers explained, noting that including them in the cell improves light absorption without reduction of the active material.

Before using the nanoparticles, the researchers examined the electrophysical and optical properties of all layers and the nanoparticles themselves, especially when they are exposed to external radiation and voltage. They then decided not to apply them to the upper transport layer, which would have prevented the light reaching the nanoparticles, as it would have been absorbed by all the layers below, and placed them, via spin-coating, in the next layer after the perovskite, which brought them closer to the light source.

The Russian-Italian research group said the paste can be used with any perovskite cell composition and architecture and that it increases manufacturing cost by only 0.3%. 'The paste can be easily applied with other methods, not only with spin coating. It's a raw universal product that can be used in other types of solar cells, as well as in the production of various devices ' photodetectors, harvesters, and optoelectronics,' the team explained. 'Such production is also environmentally-friendly, as we don't use any rare materials.'

The developed cell achieved a power conversion efficiency of 21.1%.