Molecular Photovoltaic Systems Based on Solid-Supported Phospholipids/Alkanethiol Hybrid Bilayer Matrices: Photocurrent Generation and Modulation

Abstract

Stimulated by the energy crisis and inspired by natural photosynthesis, several molecular photovoltaic (artificial photosynthetic) systems were developed and investigated within the current research. These molecular photovoltaic cells are based on solid-supported hybrid bilayer matrices which are composed of a self-assembled monolayer (SAM) of alkanethiols/octadecyltrichlorosilane and a phospholipid monolayer on gold or ITO substrate. Various chromophores including fullerenes C63, ruthenium tris(bipyridyl) complexes (Ru(bpy)32+) and zinc porphyrin (ZnP) were incorporated in the lipid layer to enable photo-excitation, charge separation and thus photocurrent generation. To further develop and improve these photovoltaics, some natural compounds, such as lutein and cholesterol, were co-assembled in the lipid layer to modulate the photocurrent and photovoltage generation by the photoactive agents. The modulation effect was also successfully applied by altering the underlying SAM layer. A combination of UV-Vis, fluorescence and impedance spectroscopy, cyclic voltammetry (CV), atomic force microscopy (AFM) as well as photoelectrochemical techniques were used to characterize and investigate these systems. This dissertation begins with an introduction to the concept of photovoltaic system and its development, the formation of solid-supported hybrid bilayer as well as the photo-sensitizers commonly used for molecular photovoltaics. Four research projects are then discussed separately, which include the investigation on the photocurrent modulation generated by fullerene C63 through co-incorporating a natural compound lutein in an alkanethiol/lipid hybrid bilayer matrix; the studies with the modulation of porphyrin and fullerene's photocurrent and photovoltage generation by using polar alkanethiol to form the underlying SAM layer as well as the involved mechanisms form several perspectives; the discussion on the dual impacts of cholesterol on lipid membranes and thus induced different effects on the photovoltaic responses of fullerene co-assembled in hybrid bilayer matrices; as well as the photovoltaic systems built on modified Indium Tin Oxide (ITO) and the difficulties of forming well-packed SAM layers on ITO surface. Which is followed by a conclusion and a brief future outlook.