HONG KONG, May 6, 2024 /PRNewswire/ -- Perovskites are among
the most researched topics in materials science. Recently, a
research team led by Prof. LOH Kian Ping, Chair Professor of
Materials Physics and Chemistry and Global STEM
Professor of the Department of Applied Physics of The
Hong Kong Polytechnic University (PolyU), Dr Kathy LENG,
Assistant Professor of the same department,
together with Dr Hwa Seob CHOI, Postdoctoral
Research Fellow and the first author of the research paper, has
solved an age-old challenge to synthesise all-organic
two-dimensional perovskites, extending the field into the exciting
realm of 2D materials. This breakthrough opens up a new field
of 2D all-organic perovskites, which holds promise for both
fundamental science and potential applications. This research
titled "Molecularly thin, two-dimensional all-organic perovskites"
was recently published in the prestigious journal
Science.
Perovskites are named after their structural resemblance to the
mineral calcium titanate perovskite, and are well known for their
fascinating properties that can be applied in wide-ranging fields
such as solar cells, lighting and catalysis. With a fundamental
chemical formula of ABX3, perovskites possess the ability to be
finely tuned by adjusting the A and B cations as well as the X
anion, paving the way for the development of high-performance
materials.
While perovskite was first discovered as an inorganic compound,
Prof. Loh's team has focused their attention on the emerging class
of all-organic perovskites. In this new family, A, B, and X
constituents are organic molecules rather than individual atoms
like metals or oxygen. The design principles for creating
three-dimensional (3D) perovskites using organic components have
only recently been established. Significantly, all-organic
perovskites offer distinct advantages over their all-inorganic
counterparts, as they are solution-processible and flexible,
enabling cost-effective fabrication. Moreover, by manipulating the
chemical composition of the crystal, valuable electromagnetic
properties such as dielectric properties, which finds applications
in electronics and capacitors, can be precisely engineered.
Traditionally, researchers face challenges in the synthesis of
all-organic 3D perovskites due to the restricted selection of
organic molecules that can fit with the crystal structure.
Recognising this limitation, Prof. Loh and his team proposed an
innovative approach: synthesising all-organic perovskites in the
form of 2D layers instead of 3D crystals. This strategy aimed to
overcome the constraints imposed by bulky molecules and facilitate
the incorporation of a broader range of organic ions. The
anticipated outcome was the emergence of novel and extraordinary
properties in these materials.
Validating their prediction, the team developed a new general
class of layered organic perovskites. Following the convention for
naming perovskites, they called it the "Choi-Loh-v phase" (CL-v)
after Dr Choi and Prof. Loh. These perovskites comprise
molecularly thin layers held together by forces that hold graphite
layers together, the so-called van der Waals forces – hence the "v"
in CL-v. Compared with the previously studied hybrid 2D
perovskites, the CL-v phase is stabilised by the addition of
another B cation into the unit cell and has the general formula
A2B2X4.
Using solution-phase chemistry, the research team prepared a
CL-v material known as CMD-N-P2, in which the A, B and X sites are
occupied by CMD (a chlorinated cyclic organic molecule), ammonium
and PF6− ions, respectively. The expected crystal structure was
confirmed by high-resolution electron microscopy carried out at
cryogenic temperature. These molecularly thin 2D organic
perovskites are fundamentally different from traditional 3D
minerals, they are single crystalline in two dimensions and can be
exfoliated as hexagonal flakes just a few nanometres thick –
20,000 times thinner than a human hair.
The solution-processibility of 2D organic perovskites presents
exciting opportunities for their application in 2D electronics. The
Poly U team conducted measurements on the dielectric constants of
the CL-v phase, yielding values ranging from 4.8 to 5.5. These
values surpass those of commonly used materials such as silicon
dioxide and hexagonal boron nitride. This discovery establishes a
promising avenue for incorporating CL-v phase as a dielectric layer
in 2D electronic devices, as these devices often necessitate 2D
dielectric layers with high dielectric constants, which are
typically scarce. Team member Dr Leng successfully addressed the
challenge of integrating 2D organic perovskites with 2D
electronics. In their approach, the CL-v phase was employed as the
top gate dielectric layer, while the channel material consisted of
atomically thin Molybdenum Sulfide. By utilising the CL-v phase,
the transistor achieved superior control over the current flow
between the source and drain terminals, surpassing the capabilities
of conventional silicon oxide dielectric layers.
Prof. Loh's research not only establishes an entirely new class
of all-organic perovskites but also demonstrates how they can be
solution-processed in conjunction with advanced fabrication
technique to enhance the performance of 2D electronic devices.
These developments open up new possibilities for the creation of
more efficient and versatile electronic systems.
Media Contact
Ms Annie Wong
Senior Manager, Public Affairs
Tel: +852 3400 3853
Email: anniewy.wong@polyu.edu.hk
View original
content:https://www.prnewswire.co.uk/news-releases/polyu-researchers-create-2d-all-organic-perovskites-and-demonstrate-potential-use-in-2d-electronics-302136395.html