Perovskite materials - Page 13

Researchers at NTU, lead by Assoc. Prof. Wang Hong, recently demonstrated high light extraction efficiency of perovskite photonic crystals fabricated by delicate electron-beam lithography.

The perovskite photonic crystals exhibit both emission rate inhibition and light energy redistribution simultaneously. They observed 7.9-fold reduction of spontaneous emission rate with a slower decay in perovskite photonic crystals due to photonic bandgap effect (PBG).

Perovskite-Info is proud to present The Perovskite Handbook. This book is a comprehensive guide to perovskite materials, applications and industry. Perovskites are materials that share a similar structure, which display a myriad of exciting properties and are considered the future of solar cells, displays, sensors, lasers and more.

Reading this book, you'll learn all about:

• Different perovskite materials, their properties and structure
• How perovskites can be made, tuned and used
• What kinds of applications perovskites may be suitable for
• What the obstacles on the way to a perovskite revolution are
• Perovskite solar cells, their merits and challenges
• The state of the perovskite market, potential and future

Researchers from Nazarbayev University in Kazakhstan and Hong Kong Polytechnic University have demonstrated a new 4-step process including (i) spin-coating of the precursors; (ii) cryogenic treatment; (iii) blow-dry process for the removal of the solvent; and (iv) thermal annealing. This process is a straightforward and effective technique which can yield homogenous perovskite films without the use of anti-solvents and regardless of the complexity of the precursor compositions.

When mixed perovskite precursor solutions are evaporated, usually non-uniform films with poor morphology are obtained due to coalescence of perovskite crystallites during rapid solvent removal. Therefore, anti-solvents are usually used to preapare mixed perovskite thin films. However, this technique is not convenient for large-scale manufacturing in industry since the final perovskite film quality critically depends on multiple parameters while adding the anti-solvent. Inaccurate control of the mixing process will cause gradients in over-saturation of the precursor solution, leading to spatially inhomogeneous nucleation of the perovskite and deterioration of the resultant film quality. Furthermore, commonly used anti-solvents such as chlorobenzene or toluene are environmentally harmful and highly toxic. The team's new method circumvents these issues and offers an improved alternative that enhances the control over the perovskite growth process, decoupling the nucleation and crystallization phases.

Researchers at Penn State have gained new insight into how halide perovskite materials enable the efficient conversion of sunlight into electricity.

Scientists state that halide perovskites tend to have a unique tolerance for imperfections in their structures, which allows them to efficiently convert sunlight into electricity when other materials with similar imperfections do not. What makes these materials so tolerant of imperfections, however, was unknown prior to this study. The researchers used ultrafast infrared imaging technology to investigate how the structure and composition of these materials influence their ability to convert sunlight into electricity.

Researchers at the University of Maryland (UMD) have identified the impact of the environment on perovskite materials. To understand the physical and chemical processes that lead to degradation, the team exposed these materials to various environmental factors in the lab and measured their response using a technique called 'in situ environmental photoluminescence (PL) to temporally and spectrally resolve the light emission within a loop of critical relative humidity (rH) levels.'

'We found that the humidity pathway determines the overall optical response of the perovskite materials, leading to a behavior called luminescence hysteresis, wherein the light emitted from the material depends not only on the current conditions but also the prior ones,' said the team. 'Further, we found that the amount of luminescence hysteresis is highly dependent on the ratio between two critical elements constituting the perovskites: Cs and Br.'

Switzerland-based Avantama demonstrated its perovskite quantum dots at Displayweek 2018. QDs are currently used as color down-conversion films to turn the emission of blue LEDs to white light.

Currently used QDs are either Cadmium-based or Indium-based, and Avantama claims that its pQDs outperform both technologies by a wide margin (3X CdSe, 12x InP), which means that using these will enable much more efficient QD-LCDs. Of course pQDs contain lead, but the amount is very small and it is way below the thresholds required by the EU and other countries.

Oxford University researchers attempted to understand what makes certain combinations of elements in the Periodic Table arrange as perovskite crystals and others not, and whether the number and nature of undiscovered pervoskites can be.

The team examined the Norwegian mineralogist Victor Goldschmidt's 1926 hypothesis known as the 'no-rattling' approach: that the formability of perovskites follows a simple geometric principle, namely: The number of anions surrounding a cation tends to be as large as possible, subject to the condition that all anions touch the cation. It basically means that if we describe a crystal using a model of rigid spheres, in a perovskite the spheres tend to be tightly packed, so that none can move around freely. Using elementary geometry, Goldschmidt's hypothesis can be translated into a set of six simple mathematical rules that must be obeyed by the ions of a perovskite.

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 Cornell used theoretical techniques to predict that using intense mid-infrared laser light on a titanium perovskite can dynamically induce a magnetic phase transition ' taking the material from its ferromagnetic ground state to a hidden anti-ferromagnetic phase. This dramatic shift could have useful applications, particularly in optical information processing.

'It would be a kind of optical switch,' the researchers said. 'You have a material where it's magnetic and 'non-magnetic.' It's going between those two states with light'.

UK-based Ossila provides components, equipment and materials to enable faster and smarter organic electronics research and discovery. Ossila provides both materials and equipment for perovskite researchers, and the company's lead perovskite scientist, Dr. Jonathan Griffin, was kind enough to answer a few questions we had for him.

Thanks to improved knowledge about salt-solvent interactions, single crystals of perovskites can now be grown. Pictured above are several single-crystal MAPbBr perovskites, alongside the seed crystals used to grow these crystals

Dr. Griffin holds nearly a decade of experience working in organic photovoltaic research and over 5 years of working with perovskites. At Ossila, Jonathan works on technical support for several material ranges, including perovskites, organic photovoltaics, graphene and other 2-D materials. He is also involved in the development of new test equipment and product ranges. Prior to this, he worked in a postdoctoral research position at the University of Sheffield.

Q: Thank you for your time Dr. Griffin. Can you detail for us Ossila's perovskite product range in general?