Novel nanoscale organic materials for optimal photovoltaic functions

Covalently linked electron donor (D) and electron acceptor (A) with conjugated organic building blocks are novel materials for potential solar cell applications, because these molecular p-n junctions can minimize the exciton diffusion and transform the charge separation from interdomain to intramolecular processes. Hence, the bottleneck of the exciton diffusion in many bulk heterojuction materials can be eliminated. Meanwhile, these planar conjugated assemblies, such as supermolecules, multiblock oligomers and polymers, have strong tendency to π-π stacking to form continuous channels for charge carriers to hop/diffuse to respective electrodes. A quartet D-A assembly has been synthesized with bis-oligothiophene (BOTH) and bisperylenediimide (BPDI) derivatives attached to a benzo template. The electronic structures and dynamics of photoinduced charge separation and recombination of this quartet molecule and reference compounds in solutions and films were studied at isolated the molecular level in solutions as well as at the molecular assembly level in films with stacked structures. Two different dynamics of charge separation and recombination associated with two types of donor/acceptor pair conformations in solution were observed. This molecular system exhibits a more efficient charge separation than charge recombination processes in both polar and non-polar organic solvents, as well as films. More efficient charge separation and slower charge recombination due to the covalent linkage indicating that the material is a potential candidate for photovoltaic studies in solid-state.