Chemistry Student Seminar: Huong Nguyen (MPhil Student)

Presenter

Huong Nguyen (Mphil - Chemistry)

Systematic coarse - graining and dynamical simulations of anisotropic molecules with applications to organic semiconductors 

Organic semiconductors are used widely in different applications, including organic photovoltaics (OPVs), devices that convert solar energy to electricity. These devices, if applicable commercially, can help to supply the world’s energy needs without requiring complicated manufacturing and maintenance. Moreover, OPVs possess several advantages over devices made from inorganic materials such as being light weight, highly transparent, and flexible.

Although experimental studies show that organic semiconductors can potentially yield high-performing devices, the electronic processes that govern the conversion of light to energy are not fully understood. Specifically, how free electrons are created and transferred within the device when a photon is absorbed is strongly debated in the literature.

Many experimental and theoretical results have shown that the microstructure at interfaces between the component organic semiconductor materials that make up the device plays an important role in these processes. This microstructure can be induced by directional forces between generally anisotropic organic-semiconductor molecules, combined with translational symmetry breaking at interfaces.

In part of the research undertaken, the molecular-level structure interface of a high-performing electron donor–acceptor OPV system consisting of two small organic semiconductors benzodithiophene quaterthiophene rhodanine (BQR) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) was studied using classical molecular dynamics (MD) for the first time.

In general, atomistic simulations are not feasible for studying donor–acceptor interface formation for the typical domain sizes found in devices. A solution to this is to use coarsegrained (CG) models, which increases the simulation efficiency by replacing a collection of atoms as a single interacting site.

We have developed a new systematic methodology to generate CG models that capture the anisotropy of molecules, which is especially useful for theoretical studies of organic semiconductors and has not previously been achieved via a systematic algorithm. To validate the method, a CG model of a simple anisotropic organic molecule (benzene) was developed.

A future application of this method will be the study of the interface structure of materials in OPV systems on realistic time and spatial scales compared to experimental conditions.

Ultimately, the studies in this work towards the same goal, which is to discover optimal molecular design rules to increase the power conversion efficiency of OPVs.