Theoretical Investigation of Dye-Sensitized Solar Cells Using Time-Dependent Density Functional Theory

Abstract

In a world where the energetic problem gains a more and more important role, research on alternative energy sources has become of fundamental importance. One of the most interesting renewable sources of energy is represented by solar cells. A breakthrough in this field was the introduction of Dye Sensitized Solar Cells (DSSCs), which have attracted considerable interest because they combine relatively high efficiency with very low production costs. DSSCs consist of dye molecules that enhance light absorption of a film or of nanoparticles made of a large gap semiconductor, such as TiO2. The main challenge in these systems is to understand the microscopic mechanisms ruling the DSSC operating processes, ultimately allowing the design of new and more efficient devices. The key process in the functioning of DSSCs is the injection of excited electrons from the dye into the semiconductor material. This process depends on the structure of the dye/semiconductor interface, and on the precise nature of the involved excited electronic states.

The computational modelling of such properties is possible using Density-Functional Theory (DFT) together with its extension to time-dependent excitation phenomena (Time-Dependent DFT, TDDFT). Such investigations are so far hindered by the very high computational cost of TDDFT calculations in very large systems. This project aims at overcoming this computational barrier by applying a recently developed recursive TDDFT method that is particularly well adapted for the calculation of optical properties in large systems. This method has already been implemented in the widely used Quantum-Espresso suite of programs. Studying the optical properties of dye covered nanoparticles using this new method will open the way to a better understanding of the physics and chemistry underlying the functioning of such solar cells.