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

Study suggests trees are crucial to the future of our cities

March 25, 2019

The shade of a single tree can provide welcome relief from the hot summer sun. But when that single tree is part of a small forest, it creates a profound cooling effect. According to a study published today in the Proceedings ...

Matter waves and quantum splinters

March 25, 2019

Physicists in the United States, Austria and Brazil have shown that shaking ultracold Bose-Einstein condensates (BECs) can cause them to either divide into uniform segments or shatter into unpredictable splinters, depending ...

Apple pivot led by star-packed video service

March 25, 2019

With Hollywood stars galore, Apple unveiled its streaming video plans Monday along with news and game subscription offerings as part of an effort to shift its focus to digital content and services to break free of its reliance ...

0 comments

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.