On the challenging objective of replacing carbon-based energy by green-renewal energy, sunlight represents a great opportunity. Among the different technologies available to convert sun energy into electricity by exploiting the photovoltaic effect, silicon cells are nowadays the most extended devices.  These devices have however some drawbacks as their high fabrication cost, its fragility, and the difficulties to integrate them in buildings and objects due to their rigidity and opacity.

In 1991 an unexplored direction in the sun energy conversion was introduced by Bryan O'Regan and Michael Grätzel with a conceptually new solar cell device based on the biomimetics of the photosynthesis in plants. In these devices, a dye sensitizer absorbs the solar radiation and transfers the photoexcited electron to a wide band-gap semiconductor electrode consisting of a mesoporous oxide layer composed of nanometer-sized particles, while the concomitant hole is transferred to the redox electrolyte, typically iodide/triiodide in solution or a hole-transporting material in the solid state.


DSSC are coloured-transparent and can use the diffuse light, moreover they are flexible and low cost, making its use very attractive for architecture and design. Although they have lower efficiencies than the conventional Si cells, a great effort is being devoted to their study and development. Under this point of view, theoretical calculations can be of great help in the design of new solar cells sensitizers with improved characteristics, providing a deep understanding of the character of the excited states involved in the absorption and injection processes.

Clearly, the ultimate goal in the theoretical simulation of DSC is the computational modeling of combined dye/semiconductor systems, investigating the dye adsorption mode onto semiconductor, the dye/semiconductor energy levels alignment and electronic coupling, the nature and localization of the excited states at the dye/semiconductor interface, the effect of surface modifications and solvation on the electronic and optical properties and the dynamics of electron injection. A further extension of these studies should also include the electrolyte.

While theoretical and computational investigations of molecular dye sensitizers are nowadays being successfully performed, the simulation of the dye/semiconductor interface is a much more complex problem that requires a multidisciplinary computational approach and a much more limited number of research groups are therefore performing these kind of investigations. We believe that the key to success in this field is definitely represented by a multi-technique computational approach which integrates different codes and techniques bridging quantum chemistry, materials science and solid-state physics.