Researchers define the perovskite ‘humidity loop’

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.”

Perovskite humidity loop image

“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.”

Avantama demonstrates its perovskite QDs at SID Displayweek 2018

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 team sets out to predict future perovskites

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.

Chinese scientists synthesize lead-free double perovskite nanocrystals

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.

Chinese team develops lead-free perovskite nanocrystals image

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.

Cornell team uses laser pulses to change the properties of a perovskite material

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”.