Savvas Hadjikyriacou

Stabilization of film morphology in polymer-fullerene heterojunction solar cells

Abstract The fixation of film morphology is essential for the long‐term stability of heterojunction polymer photovoltaic (PV) cells. An epoxy‐functionalized fullerene C60 derivative was synthesized for this purpose. This material can be polymerized at acidic conditions and was found to stabilize the phase‐separated morphologies within blended polythiophene–fullerene heterojunction films. The phase stability of the films was characterized by UV‐VIS spectroscopy and optical microscope. Crosslinkable polythiophene derivatives were also prepared but these materials were much less effective in stabilizing film morphology when mixed into PCBM (C61‐butyric acid methyl ester). Heterojunction polymer PV cells were prepared from these materials and their performance was compared with cells made from conventional materials.

Synthetic applications of nonpolymerizable monomers in living cationic polymerization : functional polyisobutylenes by end-quenching

Abstract The chemistry and kinetics of 1,1-diphenylethylene (DPE) addition to living polyisobutylene was studied at -80°C in methyl chloride/n-hexanes or methylcyclohexane 40/60 v/v. Only monoaddition occurred even when large (9-fold) excess of 1,1-diphenylethylene was used. The kinetics of addition was established by 1H-NMR spectroscopy and by conductivity measurements. The methanol-quenched polymer of the DPE-capped PIB carried exclusively –OCH3 functionality, suggesting that all diphenyl alkyl chain-ends are ionized, which was confirmed by conductivity studies. It was determined that the diphenyl alkyl chain-ends are completely ionized when [TiCl4]/[chain end] ≥ 2 for chain-end concentrations ≥ 10−3 M. Close to quantitative end-quenching was achieved with 1-methoxy-1-(trimethylsiloxy)-2-methyl-1-propene and 1-cyclohexenyloxy-trimethylsilane.

LIVING COUPLING REACTION IN LIVING CATIONIC POLYMERIZATION. 4. SYNTHESIS OF TELECHELIC POLYISOBUTYLENES USING BIS-FURANYL DERIVATIVES AS COUPLING AGENTS†

The synthesis of telechelic polyisobutylenes (PIB) by coupling with 2,5-bis-(2-furyl-2-propyl)furan is described. Hydroxyl telechelic PIB with controlled molecular weight was obtained by haloboration-initiation of isobutylene (IB) with a BCl3/BBr3 mixture, followed by coupling of the living ends and oxidation of the (CH3O)2B- end groups with H2O2 in alkaline tetrahydrofuran. Vinyl telechelic PIBs were prepared by coupling living PIB obtained using a novel vinyl functional initiator 5-chloro-3,3,5-trimethyl-1-hexene in conjunction with TiCl4 in hexanes/CH3Cl (60/40, v/v) at −80°C. Chlorosilyl telechelic PIBs were synthesized for the first time by employing chlorosilyl Functional initiators (1-chloro-1-methyl)ethyl-3-(1-dichloro-methylsilyl-methyl)ethylbenzene and 1-methyldichlorosilyl-3,3,5-trimethyl-5-chloro-hexane in conjunction with TiCl4 in hexanes/CH3Cl (60/40, v/v) at −80°C. After coupling, the dichlorosilyl groups were converted to dimethoxysilyl groups upon quenching with methanol. The bis-dimethoxysilyl telechelic PIBs were crosslinked by moisture at room temperature in the presence of catalytic amounts of tin(II) 2-ethyl-hexanoate. Extraction of the crosslinked samples with hexanes resulted in negligible soluble content, indicating essentially quantitative crosslinking. † Part 3: Ref. [10]

Aromatic Amines as Co‐sensitizers in Dye Sensitized Titania Solar Cells

Abstract Solar cells based on titania require the use of sensitizing dyes in order to make the absorption band coincident with the solar spectrum. The most successful sensitizing dyes are based on Ru‐bipyridyls and are chosen for their absorption and redox characteristics. In addition to absorbing visible light, the sensitizing dye injects an electron from its excited state into the band gap of the titania. The injected electron must be conducted through the titania to an electrode upon which the titania is coated. One of the energy wasting pathways available to the injected electron is back transfer to an oxidized dye species on the surface of the titania. We have discovered a simple means of alleviating this energy wasting pathway by anchoring aromatic amines, i.e., co‐sensitizers, at low concentration along with the Ru‐based bipyridyl sensitizing dye to the surface of titania nanoparticles. Our results indicate that there is a significant increase in cell efficiency (∼15% at AM 1.5, area ≥1 cm2) primarily due to an increase in current when these species are present on the surface in combination with the dyes. We will report our preliminary results on a series of co‐sensitizers, and we will compare these to literature findings which use similar compounds as either co‐adsorbed species on titania or as substituents on the sensitizing dye molecule itself.

Cationic Macromolecular Design Using Non(HOMO)Polymerizable Monomers

The last half decade’s development in the cationic macromolecular using non(homo)polymerizable monomers is reviewed. This process involves the intermediate capping reaction of living polyisobutylene with non(homo)polymerizable monomers, such as 1,1-diphenylethylene derivatives or 2-alkylfurans. Kinetic and mechanistic aspects of this capping reaction is discussed, and an overview of capping and coupling reactions is presented as advanced tools for the cationic design of macromolecular structures and properties. Examples are given for the synthesis of functional polymers, block copolymers, star-block copolymers, and macromonomers.