Academic Profile

Academic Profile

Prof Sum Tze Chien

Associate Chair (Research), School of Physical & Mathematical Sciences
Professor, School of Physical & Mathematical Sciences

Email: tzechien@ntu.edu.sg
Prof Sum Tze Chien

Biography
Tze Chien graduated with a B.Sc. (1st Class Hon), an M.Sc. (Accelerated Masters Program) and a Ph.D. degree in Physics from the National University of Singapore, Singapore in 1999, 2001 and 2005, respectively, where he worked on the development of a novel direct-write lithographic technique (proton beam writing) for photonic applications.

In June 2005, he joined the Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University as a Lecturer where he switched his research field from applied nuclear physics (proton beam writing and accelerator-based nuclear spectroscopy) to Femtosecond Laser Spectroscopy and its applications. Subsequently, he set up the Femtosecond Dynamics Laboratory (xC-Lab) and the Organic Electronics Laboratory; and established a new research group at the Division of Physics & Applied Physics. He was appointed Assistant Professor (tenure tracked) in 2008, promoted to Associate Professor with Tenure in Sep 2014 and subsequently to Professor in Sep 2018.

He is interested in the development and application of time-resolved and time-integrated optical spectroscopic techniques to interrogate the fundamental and applied properties of materials – i.e. probing the energy and charge transfer mechanisms in semiconducting nano-heterostructures & light-harvesting systems; as well as investigating the nonlinear optical properties of nanoscale systems.

Tze Chien received a total of 11 teaching awards from both the National University of Singapore (while he was a teaching assistant at the Department of Physics then) and the Nanyang Technological University, including the Nanyang Award for Excellence in Teaching in 2006 and the SPMS Teaching Excellence Award – Honour Roll 2010. He also set up the 1st Year Physics Teaching Laboratory, the 3rd Year Physics Teaching Laboratory and the NTU H3 Physics Teaching Labs for the MOE H3 program.

Tze Chien received several research awards: 2013 SPMS Young Researcher Award, the Institute of Physics Singapore 2014 World Scientific Medal and Prize for Outstanding Physics Research, the 2014 Nanyang Award for Research Excellence (Team) and the 2015 Chemical Society of Japan Asian International Symposium Distinguished Lectureship Award. Most recently, he is awarded the 2018 NRF Investigatorship.
Research Interests
My research focuses on investigating light matter interactions; energy and charge transfer mechanisms; and probing carrier and quasi-particle dynamics in a broad range of emergent nanoscale light emitting and light harvesting systems using Femtosecond time-resolved spectroscopy. These can be categorized under two main research themes: (1) light emitters/lasing and (2) photovoltaics. I have also established a 3rd category: (3) Aspirational Areas to explore new ideas and concepts away from my two core research themes. Specifically, I seek to address the following three questions in these systems:

(a) Where did the energy go? That is the interplay of carrier/quasi-particle dynamics between the host energy levels, defect energy levels and the dopant energy levels.

(b) What are the underlying photo-physics and light-matter interactions that give this system its unique characteristics? That is the various processes such as carrier-carrier scattering, carrier-phonon scattering, radiative recombination and auger recombination etc.

(c) How can these properties/technologies be improved for practical applications? That is how the knowledge gained be used for the development of novel optoelectronic devices; nanolasers; and photovoltaic devices.

Today, my group tackles a broad spectrum of research problems in emergent materials (such as halide perovskites, 2D materials etc) ranging from novel photophysics, solar cells, LEDs, lasing, spin phenomena, hot-carrier phenomena and nonlinear properties.

(1) Light Emitters/Lasing: We seek to understand the interplay of carrier/quasi-particle dynamics between the host energy levels, defect energy levels and the dopant energy levels and the factors affecting amplified spontaneous emission or lasing in these II-VI nanostructures such as ZnO nanowires, CdS nanowires and even the mixed dimension CdSe dot/ CdS nanorod heterostructures and organic-inorganic halide perovskites.

(2) Photovoltaics: Ultrafast optical spectroscopy allows us to trace the fate of the carriers and quasi-particles in photovoltaic devices from genesis to the end with timescales spanning over ten orders of magnitude. Correlated with electrical characterization techniques, new insights into the mechanisms of charge generation, transfer, trapping, recombination and transport in novel PV materials can be gained through these studies.

(3) Aspirational Areas: Presently, we live in a highly competitive era of rapid technological changes and shortened innovation cycles, where a keen sense and nimbleness to seek out opportunities is key to sustaining economic growth and our quality of life. These aspirational areas on 2-D Materials, novel nonlinear optical properties and spin phenomena allow us to explore new ideas and concepts apart from our core research.
Current Projects
  • Air-Stable Perovskite Quantum Dots: New Synthesis and Wavelength-Tuneable Lasing
  • Charge Transfer Dynamics at Organic-Inorganic Halide Perovskite Interfaces
  • Coupling between Surface Plasmons and Excitons: Towards Sub-wavelength Photonics
  • Energy Selective Contacts for Perovskite Hot Carrier Photovoltaics
  • Energy Transfer Mechanisms in Doped Nanoparticle Systems
  • Halide Perovskite Nanocrystals for High-order Multiphoton Microscopy
  • Interfacial Engineering for High-Efficiency Perovskite Solar Cells
  • Investigating Energy & Charge Transfer Mechanisms in Hybrid Metal-Semiconductor Nano-Heterostructures
  • Magneto-Optical Spectroscopy of Tunable Highly Spin Polarized Ferromagnetic Systems
  • Organic Solid Solar Cell Fabricated via Water-based Processing Routes ? Studies on Materials Selection and Characterization, Fundamental Photo-physics and Device Physics
  • Perovskite Optoelectronics: Multidimensional Perovskites For High Performance Solution-Processed Light-Emitting Devices
  • Perovskite Optoelectronics: Multidimensional Perovskites for High Performance Solution-Processed Light-Emitting Devices
  • Perovskite Single Crystals in Different Dimensions for Lasing and Solar Devices
  • Probing the Ferroelectric Properties of Hybrid Perovskites
  • Revolutionary Perovskites Versus Silicon for Ultrafast Active Photonic Devices
  • Room Temperature Exciton-Polariton Transistors
  • SPMS General Research Account
  • Spin Dynamics in Organo-Metal Halide Perovskite (PhD Studentship Agreement)
  • Toward Efficient Sunlight Harvesting
  • Towards >44% Perovskite Solar Cells
  • Towards Efficient Sunlight Harvesting
  • Towards Hot-Carrier Perovskite Solar Cells
  • Towards Low-Threshold Room-Temperature Hybrid Organic-Inorganic Halide Perovskite Photonic Crystal Lasing
  • Undressing the Charge-Quasiparticle-Trap Interactions in Multi-Dimensional Halide Perovskites
Selected Publications
  • Jianhui Fu, Qiang Xu, Guifang Han, Bo Wu, Cheng Hon Alfred Huan, Meng Lee Leek & Tze Chien Sum*. (2017). Hot carrier cooling mechanisms in halide perovskites. Nature Communications, 8, 1300.
  • Weiqiang Chen, Saikat Bhaumik, Sjoerd A. Veldhuis, Guichuan Xing, Qiang Xu, Michael Graetzel, Subodh Mhaisalkar, Nripan Mathews*, and Tze Chien Sum*. (2017). Giant five-photon absorption from multidimensional core-shell halide perovskite colloidal nanocrystals. Nature Communications, 8, 15198.
  • Mingjie Li, Saikat Bhaumik, Teck Wee Goh, Muduli Subas Kumar, Natalia Yantara, Michael Grätzel, Subodh Mhaisalkar, Nripan Mathews* & Tze Chien Sum*. (2017). Slow cooling and highly efficient extraction of hot carriers in colloidal perovskite nanocrystals. Nature Communications, 8, 14350.
  • Guichuan Xing, Nripan Mathews*, Swee Sien Lim, Natalia Yantara, Xinfeng Liu, Dharani Sabba, Michael Grätzel, Subodh Mhaisalkar and Tze Chien Sum*. (2014). Low-temperature solution-processed wavelength-tunable perovskites for lasing. Nature Materials, 13, 476 - 480.
  • Guichuan Xing, Nripan Mathews*, Shuangyong Sun, Swee Sien Lim, Yeng Ming Lam, Michael Graetzel, Subodh Mhaisalkar, Tze Chien Sum*. (2013). Long-Range Balanced Electron and Hole Transport Lengths in Organic-Inorganic CH3NH3PbI3. Science, 342, 344 - 347.

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