Dissertation Defense

Energy Transfer in Heterogeneous Organic Material Systems

Xiao Liu


Rapid technological developments of heterogenous organic material systems have gained significant attention over the years. Innovative molecular and thin-film morphological designs of organic heterojunctions (HJs) enable devices, such as organic photovoltaics (OPVs), to approach a market-entry-level performance. This thesis explores the fundamental physics behind the energy transfer phenomena at the HJs in an attempt to provide guidelines for high-performance device designs.

We investigated the charge transfer (CT) properties in small-molecule organic donor-acceptor blend HJs and examine the important role that delocalized CT excitons at the crystalline phase of the HJs play in efficient photocurrent generation. We also explore the energy loss mechanisms during the photogeneration process. Conjugated volume and the juxtaposition of electron donating and withdrawing groups characteristic of the molecules are associated with the exciton binding energy and electron-phonon couplings at the HJs, providing strategies to reduce energy losses and increase OPV efficiency.

I will also present the optoelectronic properties and applications of a new class of two-dimensional organic-inorganic HJ comprising a monolayer of the transition metal dichalcogenide and a thin film of the organic semiconductor.

Sponsored by

Stephen Forrest