Nav: Home

Single-particle spectroscopy of CsPbBr3 perovskite reveals the origin low electrolumine

October 09, 2019

Metal halide perovskites have recently emerged as an exceptionally promising alternative material for next generation optoelectronic applications. Especially, nanoscale-size perovskite structures posse remarkable photophysical properties, such as direct bandgap, color tunability, large absorption cross-section, and narrow photoluminescence linewidth. Together with their low cost, feasibility for scale-up synthesis, solution processability and compatibility with existing optoelectronic device components, these properties make metal halide perovskite nanocrystals a feasible alternative to other semiconducting materials for a range of light-emitting applications including displays, lighting, lasers, as well as memory devices.

However, while perovskite nanocrystals show very high photoluminescence yield, electroluminescence devices prepared from such nanocrystals have long suffered from low efficiency. Recent efforts have concentrated on device engineering to overcome this problem, but there has been so far no systematic study on the nanoscale physical origin of the poor efficiencies. Here, the team of prof. Martin Vacha from Tokyo Tech used single-particle microscopic detection and spectroscopy to study the electroluminescence process on the level of individual nanocrystals.

The team used nanocrystals of the perovskite CsPbBr3 surface-passivated with oleic acid ligands, dispersed in thin film of a conducting polymer which was used as an emission layer in a light-emitting device (LED). The device was constructed for use on top of an inverted fluorescence microscope which enabled comparison of electroluminescence and photoluminescence from the same nanocrystals. The CsPbBr3 nanocrystals form aggregates within the emission layer, with each aggregate containing tens to hundreds of individual nanocrystals. The researchers used an advanced microscopic technique of super-resolution imaging to find out that while in photoluminescence all the nanocrystals in the aggregate emit light, in electroluminescence only a small number (typically 3-7) of the nanocrystals are actively emitting (Fig. 1). The electroluminescence from only a limited number of nanocrystals is a result of size distribution and the consequent energy landscape within the aggregate. Electrical charges which are injected into the device during the operation are captured on individual nanocrystals and efficiently funneled towards the largest nanocrystals. The largest nanocrystals within the aggregate have the smallest energy bandgap, and their valence and conduction bands work as traps for charges captured originally at the surrounding nanocrystals. The conductive environment present between the nanocrystals enables efficient migration of the charges to these traps from where the electroluminescence takes place, as shown schematically in Fig. 1.

Another important finding is that the intensity of electroluminescence from the actively emitting nanocrystals is not constant but rather shows strong fluctuations, so called blinking (Fig. 1). Such blinking is not present in photoluminescence of the same aggregates. The researchers have previously found that the blinking can be caused by the conductive matrix as well as by externally applied electric field (ACS Nano13, 2019, 624). In the LED device, the blinking phenomenon is a crucial factor that contributes to the lower efficiency in electroluminescence. The researchers concluded that electroluminescence efficiency is only about one third of that of photoluminescence due to the presence of the blinking phenomenon.

The present work points a way towards efficient nanoscale characterization of electroluminescence of halide perovskite materials for light-emitting applications. One of the keys towards higher efficiency will be surface engineering of the nanocrystals that would suppress the intensity fluctuations.

Tokyo Institute of Technology

Related Spectroscopy Articles:

Unraveling the optical parameters: New method to optimize plasmon enhanced spectroscopy
Plasmon enhanced spectroscopies allow to reach single molecule sensitivity and a lateral resolution even down to sub-molecular resolution.
Nanoscale spectroscopy review showcases a bright future
A new review authored by international leaders in their field, and published in Nature, focuses on the luminescent nanoparticles at the heart of many advances and the opportunities and challenges for these technologies to reach their full potential.
Researchers combine advanced spectroscopy technique with video-rate imaging
For the first time, researchers have used an advanced analytical technique known as dual-comb spectroscopy to rapidly acquire extremely detailed hyperspectral images.
Quantum logic spectroscopy unlocks potential of highly charged ions
Scientists from the PTB and the Max Planck Institute for Nuclear Physics (MPIK), both Germany, have carried out pioneering optical measurements of highly charged ions with unprecedented precision.
Spectroscopy: A fine sense for molecules
Scientists at the Laboratory for Attosecond Physics have developed a unique laser technology for the analysis of the molecular composition of biological samples.
Fluorescence spectroscopy helps to evaluate meat quality
Scientists of Sechenov University jointly with their colleagues from Australia proposed a new, quicker and cheaper way to assess meat quality.
Single-particle spectroscopy of CsPbBr3 perovskite reveals the origin low electrolumine
Researchers from Tokyo Institute of Technology (Tokyo Tech) used the method of single-particle spectroscopy to study electroluminescence in light-emitting devices.
'Resonance' raman spectroscopy with 1-nm resolution
Tip-enhanced Raman spectroscopy resolved 'resonance' Raman scattering with 1-nm resolution in ultrathin zinc oxide films epitaxially grown on a single-crystal silver surface.
Improved functional near infrared spectroscopy enables enhanced brain imaging
In an article published in the peer-reviewed SPIE publication Neurophotonics, 'High density functional diffuse optical tomography based on frequency domain measurements improves image quality and spatial resolution,' researchers demonstrate critical improvements to functional Near Infrared Spectroscopy (fNIRS)-based optical imaging in the brain.
Raman spectroscopy poised to make thyroid cancer diagnosis less invasive
Researchers have demonstrated that an optical technique known as Raman spectroscopy can be used to differentiate between benign and cancerous thyroid cells.
More Spectroscopy News and Spectroscopy Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Climate Mindset
In the past few months, human beings have come together to fight a global threat. This hour, TED speakers explore how our response can be the catalyst to fight another global crisis: climate change. Guests include political strategist Tom Rivett-Carnac, diplomat Christiana Figueres, climate justice activist Xiye Bastida, and writer, illustrator, and artist Oliver Jeffers.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Speedy Beet
There are few musical moments more well-worn than the first four notes of Beethoven's Fifth Symphony. But in this short, we find out that Beethoven might have made a last-ditch effort to keep his music from ever feeling familiar, to keep pushing his listeners to a kind of psychological limit. Big thanks to our Brooklyn Philharmonic musicians: Deborah Buck and Suzy Perelman on violin, Arash Amini on cello, and Ah Ling Neu on viola. And check out The First Four Notes, Matthew Guerrieri's book on Beethoven's Fifth. Support Radiolab today at