Next Generation Solution-Based Materials for Low-Cost and High-Efficiency Optoelectronics

Speaker:   Prof. Kar Wei NG

Time:       10:00-12:00, Dec. 27

Location:  SIST 1A 200

Host:       Prof. Xinbo Zou

Abstract:

Novel materials which can be synthesized without extensive high vacuum and high temperature processes have long been sought for to realize high efficiency optoelectronic functionalities at low cost. In this talk, I will focus on two classes of such materials, namely carbon dots and organometallic hybrid perovskites. Carbon dots have shown great potential in various applications including biomedicines and optoelectronics. However, the origin of their photoluminescence excitation dependence still remains uncertain, and this can limit the full exploit of their wonderful optical properties. Using an alkali treatment, we thoroughly studied the mechanism for the observed excitation dependence and developed a novel strategy for tailoring of such dependence via a synergy of chemical and physical processes, thus enhancing the versatility of CDs for a broader spectrum of applications. The other class of materials, MAPbI3 (CH3NH3PbI3) and related perovskite, have received much attention because of their extraordinary optoelectronic properties, rendering them a promising low-cost material system for high-efficiency solar cells. The very fast reversible liquefaction of MAPbI3 induced by amines has been widely utilized to improve the quality of as-deposited MAPbI3 thin film for realizing high-performing devices. Despite the effectiveness, the mechanism of the liquefaction process is yet to be well understood, which may limit the further development of MAPbI3-based solar cells. Using various characterization techniques as well as First-Principles calculations, we thoroughly studied the nanoscopic reaction mechanism of the reversible liquefaction of MAPbI3 in NH3. Our understanding in the reaction mechanism not only provides important guidance on optimizing the liquefaction process for improving the performances and stability of perovskite- based devices, and open up a possible pathway for the recycling of lead, a commonly known toxin to the environment, at the end-of-life of these devices for long-term sustainability.

Bio:

Kar Wei Ng is currently an assistant professor at the Institute of Applied Physics and Materials Engineering (IAMPE) at the University of Macau. He received his BEng and MPhil degrees in Electrical and electronic engineering from the Hong Kong University of Science and Technology in 2004 and 2007 respectively. He obtained the PhD Degree in Electrical Engineering and Computer Sciences from University of California, Berkeley in 2013. Upon graduation, he joined the Taiwan Semiconductor Manufacturing Company as a principal engineer. Ng’s research focuses on correlating the nanoscopic structural properties and optoelectronics functionality in both conventional and emerging materials. His expertise lies in the monolithic integration of III-V nanostructures on silicon as well as the synthesis of high-quality perovskite-based materials and devices using liquid-based processes. In addition, he is experienced in various advanced materials characterization techniques, in particular high- resolution transmission electron microscopy and related analytical tools.

SIST-Seminar 18232