13 August 2019

[OLED] – Polymer encapsulation shields perovskite nanocrystals from degradation

Home / News / [OLED] – Polymer encapsulation shields perovskite nanocrystals from degradation
Flèche contenu
Perovskite Nanocrystal encapsulation - Codex International

Due to their fascinating optoelectronic properties, halide perovskites have attracted tremendous research interest as promising materials for photovoltaics, photodetectors, light-emitting diodes (LEDs), and lasers.
The main attractiveness of perovskite nanocrystals, which were first synthesized in 2014, is their high photoluminescence quantum yield and the possibility to tailor their emission wavelength by selecting the halide in the crystal structure. Numerous synthesis and processing innovations have delivered halide perovskite nanocrystal materials that have been tested in solar cells, solar concentrators, visible light communications, electroluminescent diodes, photodetectors, and photocatalysis.
“Despite recent achievements and a plethora of studies, perovskite nanocrystals still exhibit severe limitations for an unrestricted use in optoelectronic applications,” Prof. Dr. Alexander Urban, who leads the Nanospectroscopy Group at the Ludwig-Maximilians-University Munich, tells Nanowerk. “Akin to their bulk counterparts, the nanocrystals degrade due to external environmental influences such as humidity, heat and ultraviolet light illumination.”
In new work published in Nano Letters (“Polymer Nanoreactors Shield Perovskite Nanocrystals from Degradation”), Urban and his team report a strategy to synthesize perovskite nanocrystals using diblock copolymer micelles as a growth template.
This work constitutes a new approach for synthesizing perovskite nanocrystals of controllable size and composition with vastly improved resistance to halide ion migration and environmentally iSynthesizing the perovskite nanocrystals inside a protective polymer shell shields them from water degradation and halide ion migration yet still allows full control of their properties such as crystal size and emission wavelength.
Since energy transfer between the encapsulated nanocrystals is still possible, this technique allows for their incorporation into electronic devices.
“We showed that during our synthesis the precursor salts diffuse into the cores of the polymer micelles, where halide perovskite nanocrystals spontaneously crystallize,” notes Urban. “These exhibit strong photoluminescence as documented by quantum yields of up to 63%.”
“Notably” he adds, “the micellar-embedded nanocrystals are vastly superior to standard halide perovskites in terms of stability against humidity.”
During long-term testing, the team found that not only were nanocrystals films strongly emissive after more than 200 days of being exposed to ambient conditions but they also exhibited fluorescence after 75 days of complete submersion in water. Additionally, no halide ion migration occurred in these films.
nduced degradation.

Diblock copolymer-encapsulated perovskite nanocrystals - Codex International

“The excellent stability of the encapsulated nanocrystals combined with their ability to self-assemble in near-perfect films on substrates promises to enable the integration into optoelectronic devices,” Urban points out. “Förster resonance energy transfer (FRET) between nanocrystals of varying bandgap with an extremely high efficiency highlights a possible avenue for realizing this.”
“We still need to study the exact formation mechanisms and the specific roles of the polymer components as well as how to enable and optimize charge and/or energy transfer,” he concludes. “Nevertheless, we hope that our proposed synthesis technique significantly advances perovskite-based optoelectronics. Furthermore, block copolymers should enable subsequent nanopatterning of thin-films through photolithography and e-beam illumination, greatly expanding the range of possible device structures.”

Discover Also
[Organic Electronic] – The green chemistry of fullerene 23 February 2020

Scientists from the Skoltech Center for Energy Science and Technology (CEST) and the Institute for Problems of Chemical Physics of Russian Academy of Sciences have developed a novel approach for preparing thin semiconductor fullerene films.

Read more
[Organic Electronic] – Triazine-Acceptor-Based Green Thermally Activated Delayed Fluorescence Materials for Organic Light-Emitting Diodes 27 August 2019

High-efficiency thermally activated delayed fluorescence (TADF) is leading the third-generation technology of organic light-emitting diodes (OLEDs). TADF emitters are designed and synthesized using inexpensive organic donor and acceptor derivatives. TADF emitters are a potential candidate for next-generation display technology when compared with metal-complex-based phosphorescent dopants.

Read more