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

Recently, there has been a significant amount of work done on making photov oltaic devices (solar cells) from thin films of conjugated polymers and oth er organic systems. The advantages over conventional inorganic systems incl ude the potential to create lightweight, flexible, and inexpensive structur es. The challenge, however, has been to create more highly efficient device s. To date, the primary photovoltaic device mechanism that has been utilize d is that of photoinduced charge transfer between an electron donor and acc eptor. In this study, similar photovoltaic devices are fabricated using a w ater-based electrostatic self-assembly procedure, as opposed to the more co nventional spin-coating and/or vacuum evaporation techniques. In this proce ss, layers of oppositely charged species are sequentially adsorbed onto a s ubstrate from an aqueous solution and a film is built up due to the electro static attraction between the layers. The technique affords molecular level control over the architecture and gives bilayer thickness values of the or der of tens of angstroms. By repeating this process a desired number of tim es 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 inc luding a cationic PPV precursor, functionalized Co,, and numerous other pol yelectrolytes. We report on the device characteristics of these films and o n the overall applicability of this technique to the fabrication of photovo ltaic devices. Published by Elsevier Science B.V.