Title: Solution Processable Small Molecules for High Efficiency Organic Solar Cells
Speaker：Prof.Guillermo C. Bazan
Time: 10:30 am, April.10,2012
Place: Conference Room, Institute of Polymer Optoelectronic Materials Components
Sponsor: School of Materials Science and Engineering    
 
Abstract：Research on bulk heterojunction organic solar cells has been dominated by the use of conjugated polymers as the donor phase.  It is possible to tune the molecular structures to control the absorption profiles, for achieving proper overlap with the solar spectrum, and the orbital energy levels, for attaining high open circuit voltages with fullerene acceptors.  However, the processing of polymeric systems presents some challenges, in particular because the statistical nature of polymerization reactions yields a distribution of molecular weights and because of batch to batch variations.  Small molecule systems can circumvent these limitations but provide a different set of challenges.  For example, film formation and wetting to underlayers is more problematic.   In response, we have designed a new class of easy to prepare donor materials with intermediate molecular dimensions, which, if properly processed, can yield devices with power conversion efficiencies of 7 %.  Molecular design is critical, as well as the use of solvent additives that influence the morphology of the bulk heterojunction active layer.  These issues will be discussed in some detail, together with the techniques used for obtaining insight into the bulk organization and the internal order of the donor phases.

A short instruction to Prof.Bazan:
Professor Bazan received his Ph.D. from MIT in Inorganic Chemistry in 1991. After a postdoctoral appointment at Caltech, he joined the Chemistry Department at the University of Rochester in 1992. He joined UCSB in 1998. His current research programs are concerned with the photophysics and morphology of the organic solid state and the polymerization of olefins via homogenous catalysis. Of particular interest are strategies that control the organization of intermediate size organic chromophores in the solid state. Such methods are desirable since the relative orientation and distance of conjugated molecules control important useful properties such as conductivity and the photon processing ability of the material. Unfortunately, reliable guidelines that optimize the spatial relationship of organic molecules, especially in circumstances where hydrogen bonding is not an option, are woefully lacking. One ultimate goal is to program the maximum best morphology from the organization of atoms in the individual molecule. In the area of catalysis, the Bazan group is optimizing a multiple catalysts approach to highly branched polyethylene.