A KAIST research team has proposed a perovskite material, Cs2Au2I6 that serves as a potential active material for highly efficient lead-free thin-film photovoltaic devices. This material is expected to lay the foundation to overcome previously known limitations of perovskite including its stability and toxicity issues.

The joint team led by Professor Hyungjun Kim from the KAIST Department of Chemistry and Professor Min Seok Jang from the School of Electrical Engineering analyzed a previously discovered perovskite material, Cs2Au2I6, consisting of only inorganic substances and investigated its suitability for application in thin-film photovoltaic devices. Theoretical investigations suggests that this new perovskite material is not only as efficient but also more stable and environment friendly compared to the conventional perovskite materials.

Researchers from Sweden's Linköping University and the Nanyang Technological University (NTU) in Singapore have developed high-quality films based on double perovskites, which demonstrate promising photovoltaic properties. Developing environmentally friendly perovskites has become important in solving the toxicity issue of lead'based perovskite solar cells.

The lead-free double perovskite solar cells (yellow, in the front) compared with the lead-based device (dark, in the background)

"Our colleagues at Nanyang Technological University in Singapore have shown that the charge carriers demonstrate long diffusion lengths in the material, which is necessary if the material is to be appropriate for the application of in solar cells," says the Linköping team.

A research team at the Dalian Institute of Chemical Physics (DICP) in the Chinese Academy of Sciences synthesized a new lead-free double perovskite nanocrystals (NCs) and revealed the hot-carrier dynamic of it.

To avoid the toxicity issue of Pb, many efforts of finding a possible replacement are made. "We prepared the lead-free 3D double perovskite NCs and demonstrated that the continuously tunable emission ranged from 395 to 575 nm," said the researchers.

Researchers at Brown University and University of Nebraska - Lincoln (UNL) have come up with a new titanium-based material for making lead-free, inorganic perovskite solar cells. The team shows that the material has significant potential, especially for making tandem solar cells.

"Titanium is an abundant, robust and biocompatible element that, until now, has been largely overlooked in perovskite research," said the senior author of the new paper. "We showed that it's possible to use titanium-based material to make thin-film perovskites and that the material has favorable properties for solar applications which can be tuned."

Researchers at the University of Groningen are working on a special type of solar cell that is made of organic-inorganic hybrid perovskites. The team has been focusing on a material in which hot electrons retain their high energy levels for much longer, which might make it possible to use more of their energy to obtain a higher voltage.

Most hybrid-perovskite solar cells contain lead, which is toxic. The research group recently published a paper describing 9% efficiency in a hybrid-perovskite solar cell containing tin instead of lead. "When we studied this material further, we observed something strange", the team said. The results showed that the hot electrons produced in the tin-based solar cells took about a thousand times longer than usual to dissipate their excess energy.

Researchers at the University of Warwick in the UK designed an environmentally friendly perovskite solar cell in which lead is substituted for tin with reportedly undiminished rates of performance but at cheaper cost and with lower toxicity.

The team stated that tin-based perovskites are much more stable than previously thought, and also render solar power cheaper, safer and possibly even more commercially attractive. "The device structure can be greatly simplified without compromising performance, which leads to the important advantage of reduced fabrication cost" the scientists say.

Scientists at Oxford University have developed a solvent system with reduced toxicity that can be used to manufacture perovskite solar cells, which may clear one of the barriers to the commercialization of a technology.

By combining methylamine and acetonitrile, researchers have developed a clean solvent with a low boiling point and low viscosity that quickly crystallises perovskite films at room temperature and could be used to help coat large solar panels with the material.