Electrostatic self-assembly as a means to create organic photovoltaic devices

Recently, there has been a significant amount of work done on making photovoltaic devices (solar cells) from thin films of conjugated polymers and other organic systems. The advantages over conventional inorganic systems include the potential to create lightweight, flexible, and inexpensive structures. The challenge, however, has been to create more highly efficient devices. To date, the primary photovoltaic device mechanism that has been utilized is that of photoinduced charge transfer between an electron donor and acceptor. In this study, similar photovoltaic devices are fabricated using a water-based electrostatic self-assembly procedure, as opposed to the more conventional spin-coating and/or vacuum evaporation techniques. In this process, layers of oppositely charged species are sequentially adsorbed onto a substrate from an aqueous solution and a film is built up due to the electrostatic attraction between the layers. The technique affords molecular level control over the architecture and gives bilayer thickness values of the order of tens of angstroms. By repeating this process a desired number of times and utilizing different cations and anions, complex architectures can be created with very accurate control over the thickness and the interfaces. We have examined a number of systems built from a variety of components including a cationic PPV precursor, functionalized C60, and numerous other polyelectrolytes. We report on the device characteristics of these films and on the overall applicability of this technique to the fabrication of photovoltaic devices.