Up to now, the market of solar cells has been dominated by the conventional silicon devices. Recently, a new class of solar cells, known as dye-sensitised solar cells (DSSCs) have emerged. They are based on the hybrid chromophore/TiO2 semiconductor interface, and the low cost of manufacturing and the flexibility make them a very promising alternative to the traditional silicon cells. With this thesis, we aim at investigating theoretically, by means of density functional theory atomistic simulations, some of the current challenges in DSSCs. In particular, we will focus on the binding mode of the most common anchoring groups to TiO2, the coating of TiO2 with a second oxide such as Al2O3 to increase the efficiency, the issues related to the island growth mode during the atomic layer deposition of Al2O3 on TiO2, and the use of the delta self-consistent field method for the excitations of natural anthocyanidins. The idea is to provide experimentalists with useful guidelines for the design of devices with improved efficiencies.