Lead-free - Page 5

Researchers from the Okinawa Institute of Science and Technology Graduate University (OIST) have found that a protective layer of epoxy resin helps prevent the leakage of pollutants from perovskite solar cells (PSCs). Adding a 'self-healing' polymer to the top of a PSC can drastically reduce how much lead it discharges into the environment. This may give a boost to prospects for commercializing the technology.

'Although PSCs are efficient at converting sunlight into electricity at an affordable cost, the fact that they contain lead raises considerable environmental concern,' explains Professor Yabing Qi, head of the Energy Materials and Surface Sciences Unit, who led the study. "While so-called 'lead-free' technology is worth exploring, it has not yet achieved efficiency and stability comparable to lead-based approaches. Finding ways of using lead in PSCs while keeping it from leaking into the environment, therefore, is a crucial step for commercialization.'

Researchers at Huazhong University of Science and Technology (HUST) in China, University of Toledo in the U.S, Monash University in Australia, Jilin University and Tsinghua University in China, the Dalian Institute in China and the University of Toronto in Canada have examined a lead-free double perovskite that exhibited stable and efficient white light emission. In its mechanism of action, the material produced self-trapped excitons (STEs) due to Jahn-Teller distortion of the AgCl₆ octahedron in the excited state of the complex, observed when investigating exciton-phonon coupling in the crystal lattice.

The research team stated that a fifth of global electricity consumption is based on lighting, and efficient and stable white-light emission with single materials is ideal for such applications. Photon emission that covers the entire visible spectrum is, however, difficult to attain with a single material. Metal halide perovskites, for instance, have outstanding emission properties but contain lead, and so yield unsatisfactory stability. The perovskite in this study is, therefore, lead-free.

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.

A research team at the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences has fabricated a sensitive photodetector based on lead-free perovskite single crystals.

"We have developed a high performance photodetector based on MA3Sb2I9 microsingle crystals (MSCs)," said Prof. HAN. Scientists found that MA3Sb2I9 single crystals exhibited a low trap-state density of ~1010 cm-3, high carrier mobility of 12.8 cm2 V-1 s-1 and long carrier diffusion length reaching 3.0 μm.

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 composed of scientists from Michigan State University and University of Michigan has deployed a new approach to growing all inorganic lead-free halide perovskites.

"Epitaxial growth has long since revolutionized the study of many electronic materials including silicon, oxide perovskites, and III-V semiconductors," said Richard Lunt, an Associate Professor at Department of Chemical Engineering and Materials Science, Michigan State University who has supervised the project. "There is very little known about the epitaxial growth of halide perovskites, but these exciting materials hold enormous potential. This has motivated us to explore this entirely new research area."

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 from Sun Yat-Sen University in China have created a composite of perovskite quantum dots and graphene oxide that can reduce CO₂ when stimulated with light. It is referred to as the first known example of artificial photosynthesis based on perovskite quantum dots.

The team prepared quantum dots ' semiconductor nanoparticles ' of a highly stable cesium'lead halide perovskite, as well as a composite material made of these quantum dots and graphene oxide. Both materials showed an efficient absorption of visible light and strong luminescence. The team used these products to achieve a fundamental step in artificial photosynthesis ' the reduction of CO₂. To simulate sunlight, they used a xenon lamp with an appropriate filter.

Researchers at the Virginia Commonwealth University have identified how to control different properties and stability in perovskite-based solar cell materials using lead-free preparation. These new design principles identified super-ion building blocks, clusters of atoms that carry the same charge as the ions that they replace. Scientists can tailor these building blocks to improve stability and other desired traits, and may lead to the next generation of solar cells and optoelectronics for lighting and data storage.

a hybrid perovskite structure where the super halogens are the blue tetrahedrons, the metal atoms are green, and the alkali cation is in the middle Read more: Materials based on clusters of atoms may revolutionize the whole solar cell industry

The researchers used a multi-scale approach and a comprehensive study of over 40 materials to identify parameters and mechanism that control properties and stability in lead-free hybrid perovskites. Scientists identified design principles that correlated the ionic nature of bonding to the electronic band gap and other photovoltaic-relevant properties. The team identified two methods to increase the ionic nature: using a smaller halogen to increase the radius ratio between super-ions and using a more metallic metal (tin compared to germanium). Also, they identified how the materials degrade when exposed to moisture and proposed counter strategies.