Tze Chien Sum

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Low-temperature solution-processed photovoltaics suffer from low efficiencies because of poor exciton or electron-hole diffusion lengths (typically about 10 nanometers). Recent reports of highly efficient CH3NH3PbI3-based solar cells in a broad range of configurations raise a compelling case for understanding the fundamental photophysical mechanisms in(More)
Although being considered as one of the most promising cathode materials for Lithium-ion batteries (LIBs), LiNi1/3Co1/3Mn1/3O2 (NCM) is currently limited by its poor rate performance and cycle stability resulting from the thermodynamically favorable Li(+)/Ni(2+) cation mixing which depresses the Li(+) mobility. In this study, we developed a two-step method(More)
A facile, solvothermal synthesis of mesoporous cerium oxide nanospheres is reported for the purpose of the photocatalytic degradation of organic dyes and future applications in sustainable energy research. The earth-abundant, relatively affordable, mixed valence cerium oxide sample, which consists of predominantly Ce7O12, has been characterized by powder(More)
Hot-carrier solar cells can overcome the Schottky-Queisser limit by harvesting excess energy from hot carriers. Inorganic semiconductor nanocrystals are considered prime candidates. However, hot-carrier harvesting is compromised by competitive relaxation pathways (for example, intraband Auger process and defects) that overwhelm their phonon bottlenecks.(More)
The slow bimolecular recombination that drives three-dimensional lead-halide perovskites' outstanding photovoltaic performance is conversely a fundamental limitation for electroluminescence. Under electroluminescence working conditions with typical charge densities lower than 1015 cm-3, defect-states trapping in three-dimensional perovskites competes(More)
Organic-inorganic halide perovskites (e.g., CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>) possesses exceptional optoelectronic properties for photovoltaics. Amazingly, this material system also has outstanding optical gain properties ideal for lasing applications. Two years had elapsed since the discovery of amplified spontaneous emission and lasing from(More)
Formamidinium lead halide (FAPbX3) has attracted greater attention and is more prominent recently in photovoltaic devices due to its broad absorption and higher thermal stability in comparison to more popular methylammonium lead halide MAPbX3. Herein, a simple and highly reproducible room temperature synthesis of device grade high quality formamidinium lead(More)
Ultrafast spin manipulation for opto-spin logic applications requires material systems that have strong spin-selective light-matter interaction. Conventional inorganic semiconductor nanostructures [for example, epitaxial II to VI quantum dots and III to V multiple quantum wells (MQWs)] are considered forerunners but encounter challenges such as lattice(More)
Organic-inorganic metal halide perovskites have recently demonstrated outstanding efficiencies in photovoltaics as well as highly promising performances for a wide range of optoelectronic applications such as lasing, light emission, optical detectors, and even for radiation detection. Key to the realization of functional perovskite micro/nanosystems on the(More)
Saturable absorption of graphene was experimentally and theoretically investigated in femtosecond time regime with the z-scan technique. The initial ultrafast carrier relaxation time was determined to be &#x223C;8(&#x00B1;3) fs. Such ultrafast dynamics is far beyond the time resolution of other ultrafast techniques with typical hundred fs laser pulses. Our(More)
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