Title: Understanding Charge Carriers Transport and Recombination Pathways in TMD-based Heterojunctions Through Photoelectrochemical Microscopy

Speaker: postdoctor Li Wang, Colorado State University

Date: 2020-01-14 16:00

Location: Room 234， Chemistry Building

Abstract：

Van der Waals heterojunctions are attractive for solar energy conversion applications because light excitation produces carriers at charge-separating interfaces. The energy level offset at the interface drives charge separation on the femtosecond time scale. Current understanding of charge transport and recombination processes that follow the ultrafast charge separation step is mainly derived from solid-state device geometries where the TMDs are stacked on top of each other and electrical contacts are deposited on TMD edges. In this geometry, charge transport takes place parallel to the layers across micron-scale distances, thus resulting in the transport-limited device physics. Furthermore, these systems are not well-suited to represent real cases, especially in catalytical systems, where other factors as solid-liquid interfaces, surface defects/absorbates, dielectric environments could alter the carrier behavior. Based on a home-built photoelectrochemical microscopy system, we could tackle these problems through an efficient and high-throughput photocurrent mapping approach. At the same time, spatial-resolved, single-flake-level, structure-function relation based on 2D systems could be built.

Biography:

Dr. Li Wang received his B.S. from Wuhan University in 2009. Then he went to Changchun Institute of Applied Chemistry (CIAC, CAS) for his Ph.D focusing on the synthesis of organic semiconductor for use as active layers in organic thin-film transistors (OTFTs) and organic solar cells (OSCs). After graduation in 2014, he started his postdoc with Prof. Wenfang Sun at North Dakota State University (NDSU), where he switched to organometallic complexes synthesis and exploring chemical approach to long-lived triplet states in ruthenium and iridium complexes for nonlinear optics and phototherapeutics. In 2017, he moved to Colorado State University to work with Prof. Justin Sambur on ultrathin photovoltaics. Through a home-built microscope-based system, photocurrent maps originated from iodide oxidation on 2D TMDs could be reconstructed and compared with both in-situ/exsitu structural information.