Heterostructures and interfacial layers for polymer solar cells

This thesis is concerned with the study and the development of bulk heterostructures and interface layers for polymer solar cells. A polymer solar cell structure involves several layers, from the transparent conducting oxide (TCO) to top metallic electrodes, from the hole (HIL) and electron interface layers (EIL) to the active polymers. Starting from the generic structure (TCO/HIL or EIL/Active polymers/EIL or HIL/Metal), a systematic study on over 10 materials, among which different TCOs, metal oxides, organic and inorganic compounds as interface layers, metals as top electrodes and different active polymers, was carried out. Combining the most common materials in over 20 different architectures enabled me to clarify, thanks to support from simulations, the relationship between open circuit voltage and the difference between the work function values of the two opposite interface layers/contacts, a matter that until now was still under debate. Furthermore, innovative electrodes, active polymers and fabrication techniques have been here demonstrated to be promising candidates for polymer photovoltaics (PV). Not only improvement in solar cell performance was achieved, but also investigations on the influence of the electrode/active interfaces were carried out by electroabsorption (EA) spectroscopy to understand the physics behind the enhancement of the solar cell performances. Finally, a study on neutron radiation tolerance of polymer solar cells was investigated to demonstrate the feasibility for space applications. The results of this thesis are an overall study of polymer PV. The approach used in this thesis can be extended to other photoactive and contact layers used in the polymer solar cells in order to clarify the electrode influence on other photovoltaic parameters (i.e. current density, fill factor and power conversion efficiency) and even to develop new promising materials.