Perovskite materials - Page 11

Scientists at Stanford University and the Department of Energy's SLAC National Accelerator Laboratory have used a novel method, based pressure from a diamond anvil cell, to stabilize lead halide perovskites and prevent them from breaking down at room temperature.

The team placed the regular version of the material, prone to instability, in a diamond anvil cell and squeezed it at a high temperature. This treatment reportedly "nudges" its atomic structure into an efficient configuration and keeps it that way, even at room temperature and in relatively moist air.

The University of Macau (UM) Institute of Applied Physics and Materials Engineering (IAPME) and Nanjing Tech University jointly developed a method to prepare phase-pure quasi two-dimensional (2D) metal-halide perovskites, which could be used for constructing stable perovskite solar cells.

The very low formation energy of the typically used three-dimensional (3D) perovskites accounts for their low stability and hinders the commercialization of perovskite optoelectronic devices. Recent studies show that the dimensionality of deposited perovskites could be reduced from 3D to quasi 2D by introducing an appropriate amount of long organic cations into the precursor solution, which can greatly improve the stability of perovskites thanks to the protection offered by the organic cation layer on the surface. However, such 2D perovskites typically consist of multiple quantum wells with a random well width distribution because of the thermodynamic stability of compounds in the solution. The thick quantum wells and 3D perovskite within the deposited film will still limit the overall stability of the material. Therefore, the deposition of phase-pure quasi 2D perovskite remains a key scientific challenge.

A collaboration between University of Pennsylvania, Seoul National University, the Korea Advanced Institute of Science and Technology, the Ecole Polytechnique Fédérale de Lausanne, the University of Tennessee, the University of Cambridge, the Universitat de Valencia, the Harbin Institute of Technology, and the University of Oxford has yielded an understanding of how a class of electroluminescent perovskite materials can be designed to work more efficiently.

This latest work is based on a past endeavor by Penn theoretical chemist Andrew M. Rappe and Tae-Woo Lee at Seoul National University to develop a theory to help explain experimental results. The material that was studied was formamidinium lead bromide, a type of metal-halide perovskite nanocrystal (PNC). Results collected by the Lee group seemed to indicate that green LEDs made with this material were working more efficiently than expected. 'As soon as I saw their data, I was amazed by the correlation between the structural, optical, and light-efficiency results. Something special had to be going on,' says Rappe.

Researchers at the Department of Energy's SLAC National Accelerator Laboratory and Stanford University have used the lab's X-ray laser to watch and directly measure the formation of polarons for the first time. Polarons are fleeting distortions in a material's atomic lattice that form around a moving electron in a few trillionths of a second, then quickly disappear. Despite their transient nature, they do affect a material's behavior, and may even be the reason that solar cells made with lead hybrid perovskites achieve extraordinarily high efficiencies in the lab.

Polaron 'bubbles' of distortion form around charge carriers ' electrons and holes that have been liberated by pulses of light ' which are shown as bright spots here. Image by SLAC

Perovskite materials are famously complex and hard to understand, according to Aaron Lindenberg, an investigator with the Stanford Institute for Materials and Energy Sciences (SIMES) at SLAC and associate professor at Stanford who led the research. While scientists find them exciting because they are both efficient and easy to make, raising the possibility that they could make solar cells cheaper than today's silicon cells, they are also highly unstable, break down when exposed to air and contain lead that has to be kept out of the environment.

Researchers at Ecole Polytechnique Fédérale de Lausanne (EPFL), assisted by teams at Croatia's University of Split, have developed a perovskite that can detect gamma rays.

The 'oriented crystal'crystal growth' (OC2G) method of large MAPbBr3 crystals . a) Growing of large crystals by the suspended seed crystal; b,c) The consecutive steps of fusing together individual single crystals into a large crystal. Image by EPFL

"This photovoltaic perovskite crystal, grown in this kilogram size, is a game changer," says EPFL's Professors Lászlo Forró. "You can slice it into wafers, like silicon, for optoelectronic applications, and, in this paper, we demonstrate its utility in gamma-ray detection."

Researchers at Duke have examined crystalline metal halide perovskites (MHPs), and found that while crystallinity offers numerous advantages, the ability to access a glassy state with distinct properties can provide unique opportunities to extend the associated structure'property relationship, as well as broaden the application space for MHPs.

Amorphous analogs for MHPs have so far been restricted to high pressures, limiting detailed studies and applications. In their new work, the Duke team structurally tailored a 2D MHP using bulky chiral organic cations to exhibit an unusual confluence of exceptionally low melting temperature (175 °C) and inhibited crystallization.

India-based researchers have recently designed a novel synthesis procedure that can produce highly uniform luminescent perovskite nanocrystals with uncommon shapes and surface morphologies.

Their work broadens the range of strategies that can be used for tuning the optical and photonic properties of these materials, which are widely studied for use in solar cells, light-emitting diodes, and electronic displays.

A research team, jointly led by Professor Gun-Tae Kim and Professor Jun-Hee Lee in the School of Energy and Chemical Engineering at South-Korea's UNIST has succeeded in developing high-performance perovskite oxide catalysts using late transition metal oxide materials. In the process, the team discovered the reason behind the improved performance of both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which has been explained by the change in the oxidation state of the transition metal caused by the increase in oxygen vacancies.

Perovskite oxide catalysts are composed of lanthanide, transition metal and oxygen. Owing to the excellent electrical conductivity and bifunctional ORR/OER activity, these catalysts have been considered to be an attractive candidate for metal-air batteries or fuel cells, in which opposite reactions, such as charging and discharging occur steadily. However, due to the high cost and low stability of noble metal catalysts, the development of alternatives is strongly desired.

Researchers at HZB have reported findings from their recent work: printing and exploring different compositions of caesium based halide perovskites (CsPb(Br_xI_1'x)₃ (0 ≤ x ≤ 1)).

In a temperature range between room temperature and 300 Celsius, the team observed structural phase transitions influencing the electronic properties. The study presents a quick and easy method to assess new compositions of perovskite materials in order to identify potential candidates for applications in thin film solar cells and optoelectronic devices.

Researchers at Linköping University in Sweden have announced the development of an optoelectronic magnetic double perovskite. The discovery could open the door to combining spintronics with optoelectronics for rapid and energy-efficient information storage.

The team explains that one type of perovskite that contains halogens and lead has recently been shown to have interesting magnetic properties, opening the possibility of using it in spintronics. Spintronics is thought to have huge potential for the next generation of information technology, since information can be transmitted at higher speeds and with low energy consumption. However, magnetic properties of halide perovskites have until now been associated only with lead-containing perovskites, which has limited the development of the material for both health and environmental reasons.