Andriy Kovalenko

Density Functional Investigation of Charge Transfer in Organic Solar Cells

A germafluorene based polymer, (PGFDTBT), is one of the polymers which is a promising candidate for plastic electronics [1]. PGFDTBT is already used with C60 in solar cells. In order to understand the underlying mechanism of the charge transfer in the bulk hetereojunction of this solar cell, we carry out the density functional investigations at the interface of a PGFDTBT and C60. We study the ground state as well as excited state geometry and detailed electronic structure of the interface. The charge transfer is studied using the charge densities of the orbitals near the HOMO and LUMO. Our results indicate that the charge transfer at the ground state of Polymer:C60 interface is negligible, while the efficient charge transfer from polymer to C60 takes place upon excitation. The transfer is also followed via the charge transfer state which is energetically in between the charge separated state and the excited state.

Molecular Modeling of Biomolecules and Solutions in Nanoporous Materials

As one goes down the length scale to nanoworld, the properties of objects and phenomena swerve from those described by the conventional, macroscopic laws governing the behavior of continuous media and materials. The functional features of nanostructures manifest on length scale from one to hundreds nanometers and time scale up to microseconds and more, but all stem from microscopic properties of the atoms and chemical groups they are built of. Explicit molecular modeling of such nanosystems involving millions of molecules is by far not feasible with ab initio methods and molecular simulations, and requires multiple-scale approaches. Statistical-mechanical theory of molecular liquids and other disordered systems successfully describes the molecular structure and thermodynamics of nanosystems, with proper account of their chemical functionalities.¹-⁴ It operates with spatial/temporal distributions of species averaged over the statistical ensemble rather than with trajectories of individual molecules. This coarse-graining, however, keeps the short-range detail of the solvation structure of chemical specificities, such as the hydrophobic effects, hydrogen bonding, and other association effects. Below discussed are two illustrative examples, self-assembly of organic nanotubes in electrolyte solution and electrochemical devices with nanoporous electrodes.