Novel Organic and Polymeric Materials for Solar Energy Conversions

Organic or ‘plastic’ solar cells are attractive for solar photoelectric energy conversion applications where low cost (such as large area), lightweight, and flexible shape are desired. The photoelectric power conversion efficiencies of currently reported organic/polymeric photovoltaic materials are still relatively low (typically less than 10% under AM 1.5 and one Sun intensity), and the three major losses are still severe, i.e., the ‘photon loss’ due to mismatch of materials energy gaps versus the sunlight photon energies, the ‘exciton loss’ and the ‘carrier loss’ due to poor solid state morphologies of existing polymeric donor/acceptor binary systems. Therefore, both molecular frontier orbitals (HOMOs, LUMOs) and phase morphologies need to be engineered to further enhance the efficiency. In this paper, our recent efforts on frontier orbital and energy gap engineering and terminal functionalizations of conjugated polymer blocks, and a donor-bridge-acceptor type block copolymer approach will be reviewed. For instance, a new donor-bridge-acceptor or DBA type conjugated block copolymer system has been successfully synthesized, characterized, and solar cells based on the new materials has been preliminarily tested revealing better performance of the block copolymer system versus the donor/acceptor simple blend system. In addition, dye sensitized polymer and organic/inorganic hybrid nanostructure solar cells were also investigated as dyes absorb more sunlight photon and have more available energy levels and gaps that can better match the solar spectrum than traditional solar cells.