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Friday, March 15

Solar Energy Conversion Using Artificial
Atoms, Molecules, and Solids

Tianquan Lian, Emory University, Atlanta, Ga.
Chemical Sciences Division Seminar
10:00 AM — 11:00 AM, Chemical and Material Sciences Building (4100), Room C-201
Contact: Deen Jiang (, 865.574.5199


Quantum confined semiconductor nanocrystals have been widely investigated as light harvesting and charge separation components in photovoltaic and photocatalytic devices. Interest in these materials has intensified in recent years due to reports of multiexciton generation in semiconductor nanocrystals and devices. Compared with single component quantum dots (or "artificial atoms"), semiconductor nanoheterostructures (or "artificial molecules"), which consist of two or more component materials, offer additional opportunities to control their charge separation properties by tailoring their compositions and dimensions through wave function engineering. In a series of recent studies, we showed that the efficiency of single and multiple exciton dissociation from semiconductor nanocrystals could be effectively controlled. With (quasi)-type II band alignment, forward reactions (charge separation and hole filling) could be facilitated, while the backward recombination (charge recombination and exciton-exciton annihilation) could be simultaneously retarded, enhancing the charge separation efficiency. We achieved near-unity quantum yield of redox mediator (methylviologen radical) generation with asymmetric CdSe/CdS dot/rod nano-heterostructures. When coupled with catalysts (Pt), these nanorods led to a much higher solar-driven hydrogen generation efficiency compared to molecular dyes and other nanocrystals. In ongoing work, we show that these materials can form "artificial solids," facilitating their integration in photoelectrochemical water splitting devices. (Relevant recent publications: JACS(2012),134, 4250&10337&11701&11289)

About the speaker:
Biographical sketch. Tianquan (Tim) Lian received his PhD degree from University of Pennsylvania (under the supervision of Prof. Robin Hochstrasser) in 1993. After postdoctoral training with Prof. Charles B. Harris in the University of California at Berkeley, Tim Lian joined the faculty of chemistry department at Emory University in 1996. He was promoted to associate professor in 2002, full professor in 2005, Winship distinguished research Professor in 2007, and William Henry Emerson Professor of Chemistry in 2008. Tim Lian is a recipient of the NSF CAREER award and the Alfred P. Sloan fellowship. Tim Lian research interest is focused on ultrafast dynamics in photovoltaic and photocatalytic nanomaterials and at their interfaces.