Atomistic investigation of structure and optoelectronic properties of hybrid polymer/ZnO interfaces

Hybrid interfaces are attracting increasing interest for photovoltaic applications due to their low cost of production compared to traditional silicon-based systems and easy processability. This is the case of polymer/metal oxide systems. In particular, hybrid P3HT/ZnO can be considered as a possible alternative to organic solar cells because, by replacing the organic electron acceptor with the inorganic metal oxide it is, in principle, possible to improve the stability as well as the durability of the system. In this thesis, by means of a combination of large scale molecular dynamics simulations and ab initio methods, we study at the atomic scale the interface between the polymer P3HT and the ZnO crystalline surface. We investigate the structure and morphology of the polymer at the interface at low and room temperature, we characterize in detail the polymer disorder close to the ZnO surface and we discuss the implications of this disorder on transport properties. Furthermore, we investigate the possible presence of residual molecules of solvent at the interface after the synthesis process, that can affect the properties of the interface. A novel strategy to improve the polymer/metal oxide interface is proposed and investigated. Specifically, we study the deposition and assembling of zinc phthalocyanine molecules on ZnO and we investigate the modification of the P3HT/ZnO interface, induced by the use of a ZnPc optically active molecular interlayer. The structure and morphology of the ZnO/ZnPc/P3HT system, studied by molecular dynamics simulations, are used as starting point for DFT calculations. We discuss the electronic and optical properties of this ternary system reporting indications of an improvement in hybrid photovoltaic devices due to the hindering of the charge recombination and a better exploitation of the solar spectrum. This kind of architecture, theoretically designed by a multiscale predictive modeling in the present thesis, is an example of a novel class of systems whose performances are currently under experimental investigation.