The use of polystyrene-tethered fullerenes as stabilizers in bulk heterojunctions

Self-assembly of nanoparticles can potentially provide improvements for many current applications and could influence the design of future technologies. The assembly of nanoparticles, which can be controlled through external forces or through molecular interactions, can affect the properties of a material. Nanoparticles can be chemically modified by attaching molecules such as polymers to their surface. The nature and placement of these tethers affects the arrangement of the nanoparticles leading to materials with novel chemical, electrical, and physical properties.;In this research, the assembly of the fullerene (C60) based nanoparticles was modified using polystyrene-tethered fullerenes (PTFs) as additives. Polystyrene (PS) was synthesized via atom transfer radical polymerization and fully characterized by GPC and IR. The PS was attached to C60 using atom transfer radical addition, azide coupling, and by the addition of CN- to the C60 creating a nucleophile that reacted with bromine terminated PS. PTFs were characterized using GPC with a UV-Vis detector and TGA to determine percent C60. This study focuses on the synthesis and characterization of PTFs and the use of PTFs as an additive in organic photovoltaics (OPVs).;The size of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) domains within the bulk heterojunction (BHJ) of OPVs is of great importance to the performance and lifetime of the device. PTFs were used as an additive in the BHJ to reduce the initial PCBM domain size as well as to mitigate the growth of these domains over time that typically results in decreased device efficiency. Films were prepared from a mixture of PCBM:P3HT on silicon wafers to approximate a BHJ system. PTFs were added in concentrations ranging from 0% to 20%. The samples were then annealed at 150°C for varying times ranging from 5 to 60 mins and examined by SEM to determine the average PCBM domain sizes for each sample. As expected, the control sample containing no additive showed significant growth in the PCBM domains as the sample was annealed with a final average domain size of 290 microm2. However, addition of as little as 5% PTFs produced average PCBM domain sizes after 60 minutes of annealing of 28 microm2. Addition of 20% PTF resulted in an average PCBM domain size of 2 microm2. Based on these encouraging results, devices containing these architectures were prepared.;Using PTFs with the PS molecular weights of 1K, 2K, and 6K, devices were fabricated. To reduce the amount of PS, low concentrations (<5%) of the tether were used. The concentration of PTF is based on the amount of PCBM replaced. Devices containing the PTF additives showed significant improvement over the control during annealing. The devices containing 1% 1K and 1% 2K PTFs had a ≈50% increase in energy output, and the devices containing 1% 6K PTF showed a 14% increase in energy output over the annealing period.