Sum Tze Chien

Biography

Tze Chien graduated with a B.Sc. (1st Class Hon), a 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 had 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 promoted to Assistant Professor (tenure tracked) in 2008 and was subsequently promoted to Associate Professor with Tenure in Sep 2014. 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 nano-scale systems.

Research Interest

My current 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) nanophotonics and lasing and (2) photovoltaics. Specifically, I seek to address the following three questions in these systems: (i) 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. (ii) 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. (iii) 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. 1. Nanophotonics and 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 (CH3NH3PBI3). My most outstanding research work in Nanophotonics and Lasing to date is my Nature Materials (Mar 2014) paper on the discovery of CH3NH3PbI3 as an excellent optical gain medium for lasing (80 cites - Google Scholar - 03 Apr 2014). 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. My most outstanding research works in photovoltaics to date are (i) the Nature Communications (June 2013) paper on uncovering the loss mechanisms in Ag-nanoparticle blended bulk heterojunction plasmonic organic solar cells using ultrafast optical spectroscopy (25 cites - Google Scholar - 03 Apr 2014); and (ii) the Science paper (Sep 2013) on discovering the long-range balanced electron and hole transport lengths in organic-inorganic CH3NH3PbI3 (456 cites - Google Scholar - 03 Apr 2014).