Research

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POLARON DYNAMICS IN LEAD HALIDE PEROVSKITES

We seek to understand the exceptional carrier properties in lead halide perovskites from the viewpoint of polarons, the quasi particles of carriers associated with surrounding lattice distortion. Specifically, we propose the ferroelectric polaron concept to explain the efficient screening of charge carriers. We extend the idea to other ferroelectric and paraelectric semiconductors as basis for defect tolerant semiconductors.

Nature Mat. 2018, 17, 379-381

Science Adv. 2017, 3, e1701217

Science, 2016, 353, 1409-1413.

 

 


SAS

SUPERATOM SOLIDS

Superatom solids are a new class of materials assembled with nanoscale building blocks of superatomic motifs. This synthetic approach allows us to manipulate material structures and their optical, electronic, and magnetic properties. We can tune optical gaps broadly from mid-IR to the visible region, and control the structural dimensions between 0D, 1D, 2D, and 3D. We are studying emergent properties of the materials with optical spectroscopies and scanning-tunneling microscopy.

Adv. Mat. 2019, 30, 1903209

Adv. Funct. Mater. 2019, 29, 1902951

Nano Lett. 2018, 18, 1483-1488

 

 


2D

TWO-DIMENSIONAL MATERIALS

We use optical pump-probe spectroscopies and time- and angle-resolved photoemission spectroscopy  to study excitons and carriers in two-dimensional semiconductors, such as transition metal dichalchogenides (TMDCs). Of particular interest are excitonic phase transitions in TMDC heterobilayers.

Phys. Rev. Lett. 2019, 122, 246803

Science Adv. 2019, 5, eaax0145

Nature Mat. 2018, 17, 411-415

 

 


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SINGLET FISSION

Singlet fission is the photo-chemical process where one singlet exciton splits into two triplet excitons. The exciton multiplication process can potentially boost the performance of a single-junction solar cell, a photo detector, and perhaps a multi-electron photocatalyst, but the microscopic understanding of singlet fission is necessary. We use multiple ultrafast spectroscopic techniques to understand the singlet fission rates and to explore the harvesting of triplets from the singlet fission process.

Nature Chem. 2017, 9, 341-346.

Science Adv. 2017, 3, e1700241.

J. Am. Chem. Soc. 2019, 141, 13143-13147

 

 


nmat4271-f3

LIGHT-MATTER INTERACTIONS

We study the fundamental interaction of light with matter, such as lasing and polariton condensates in low-dimensional cavities. In particular, we aim to understand the fundamental scattering processes responsible for polariton condensation and coherent light emission.

Nature Commun. 2019, 10, 265

Acct. Chem. Res. 2019, 52, 2950-2959

Nat. Mater. 2015, 14, 636-642.

 

 


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CHARGE TRANSFER

The van der Waals interfaces of molecular donor/acceptor are central to concepts and emerging technologies of light-electricity interconversion. Examples include, among others, solar cells, photodetectors, and light emitting diodes. A salient feature in van der Waals interfaces is the poorly screened Coulomb potential that can give rise to bound electron–hole pairs across the interface, i.e., charge transfer (CT) excitons. We are studying these processes with a range of optical and photoelectron probes.

J. Am Chem. Soc. 2015, 137, 8313-8320.

Phys. Rev. Lett. 2015, 114, 247003.