Molecularly thin hybrid perovskite for advanced optoelectronic applications

December 7, 2018, National University of Singapore
Figure 1: (a - e) Optical image of large sized 2D hybrid perovskites (single crystal) and different homologous series (compounds with the same functional group but differ by the number of repeating units) from n = 1 to n = 4. (f - j) Schematics showing the structure of the unit cell. (k - o) Atomic force microscopy images and profile of the exfoliated single unit cell perovskite layers. Credit: National University of Singapore

NUS scientists have discovered that the light emission properties of molecularly thin two-dimensional (2-D) hybrid perovskite can be tuned in a highly reversible way for ultrathin optoelectronic applications. A highly efficient photodetector has been fabricated using hybrid perovskites with the thickness of a single quantum well.

Layered perovskites are solution processible, low-cost materials that can be used as photo detectors or emitters. The superior ability of the crystal to detect and emit light with is expected to find practical applications in various fields. Each basic unit of a 2-D hybrid perovskite is constructed using a semiconducting of inorganic material sandwiched between two organic insulating layers. While researchers have studied layered perovskites in their bulk form for the past thirty years, the properties of these crystals when their thickness is thinned down to a few and single layers have largely not been explored.

A led by Prof Loh Kian Ping, from the Department of Chemistry, NUS has discovered that a molecularly thin layer of perovskite can be strained in a highly reversible manner without introducing permanent defects on the material that can affect its light emission properties. Also, the emission properties of the perovskite can be tuned reversibly under repeated strains. The researchers achieved this by encapsulating the surface of the perovskite with a of optically transparent hexagonal boron nitride. This barrier layer traps the on the surface of the perovskite layer, preventing them from escaping into the air even under strong laser irradiation.

Using a temperature controlled crystallisation method, the researchers synthesised centimetre-sized perovskite single crystals of the Ruddlesden-Popper phase (a form of layered perovskite structure). These specially prepared crystals are much larger than the usual micron-sized ones and allowed the team to peel off thin layers from it using the "scotch tape" method (similar method used for obtaining graphene from graphite). These ultrathin crystals were then used for the experiments.

Molecularly thin hybrid perovskite for advanced optoelectronic applications
Figure 2: An artist’s impression of laser interaction with a molecularly thin 2D perovskites encapsulated by hexagonal boron nitride (blue layer). Credit: National University of Singapore

Prof Loh said, "Unlike bulk perovskites where the organic chains of adjacent layers are interdigitated and tightly-packed, the layer of organic chain on ultrathin perovskites can "relax" more easily under laser or thermal activation. This "relaxation" process changes their light emission properties. We found that the light emission can reverse back to its initial state by constraining ("de-relaxing") the surface of the ultrathin perovskite layer."

"We have also studied the atomic structure of these perovskites using the QPlus atomic force microscope. Depending on the supplied thermal energy, the organic layers on the surface can assemble and change the optoelectronic properties of the crystal in a reversible manner. This could potential be used for developing strain-tuneable optoelectronic devices," added Prof Loh.

Explore further: High-performance solar cells: Physicists grow stable perovskite layers

More information: Kai Leng et al. Molecularly thin two-dimensional hybrid perovskites with tunable optoelectronic properties due to reversible surface relaxation, Nature Materials (2018). DOI: 10.1038/s41563-018-0164-8

Related Stories

Perovskite edges can be tuned for optoelectronic performance

March 9, 2017

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating innovative 2D layered hybrid perovskites that allow greater freedom ...

Recommended for you

Artificially produced cells communicate with each other

January 18, 2019

Friedrich Simmel and Aurore Dupin, researchers at the Technical University of Munich (TUM), have for the first time created artificial cell assemblies that can communicate with each other. The cells, separated by fatty membranes, ...

3-D culturing hepatocytes on a liver-on-a-chip device

January 17, 2019

Liver-on-a-chip cell culture devices are attractive biomimetic models in drug discovery, toxicology and tissue engineering research. To maintain specific liver cell functions on a chip in the lab, adequate cell types and ...

This computer program makes pharma patents airtight

January 17, 2019

Routes to making life-saving medications and other pharmaceutical compounds are among the most carefully protected trade secrets in global industry. Building on recent work programming computers to identify synthetic pathways ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.