Nanocrystalline TiO2 amphoteric colloidal charged particles and polyelectrolytes have been used to fabricate a dye-sensitized solar cell. Two weak polyelectrolytes, poly(allylamine hydrochloride) and poly(acrylic acid), and two strong polyelectrolytes, poly(dimethyldiallylammonium chloride) (PDAC) and poly(sodium 4-styrenesulfonate), have been utilized to assemble polyion/TiO2 nanocomposite multilayered films by the electrostatic layer-by-layer deposition technique. The layer-by-layer assembly of the TiO2 nanoparticles proceeds linearly as shown by sequential UV−vis absorption and thickness measurements. The morphology of these assemblies was characterized using atomic force microscopy. The nanoporous polyion/TiO2 films were sintered and used as working electrodes for cis-di(thiocyanato)-N,N-bis(2,2‘-bipyridyldicarboxylate)-ruthenium(II) (N3) sensitized solar cells. I−V characteristics of the solar cells made by the calcinated polyelectrolyte/TiO2 electrodes show several interesting results. (i) The short-circuit current does not linearly increase with the thickness of the TiO2 electrode, even though the adsorption behavior of the N3 dye shows a linear increase. (ii) The precursor polyelectrolytes used to assemble TiO2 play a major role in the photovoltaic performance of the solar cells. Thermogravimetric analysis studies show that the thermal stability of the polyelectrolytes may have a direct effect on the overall device efficiency. (iii) The photovoltaic performance of these solar cells is comparable to that of cells made by other methods such as spin casting, the layer-by-layer technique offers unsurpassed control in manipulating the final device thickness. An efficiency of 7.2% was obtained for the solar cell made from PDAC/TiO2 (200 bilayers) precursor film, under 1 sun at simulated Air Mass 1.5 direct irradiation.

The purple membrane (PM) containing bacteriorhodopsin (BR) is a promising biomaterial for many potential optical and optoelectronic device applications. Organized, heterogeneous assemblies using polycationic poly(dimethyldiallylammonium chloride) (PDAC) and PM fragments have been successfully constructed by the spontaneous alternating adsorption of PDAC and PM. The fabrication process of the multilayers was followed by UV−vis absorption spectroscopy and ellipsometry. The results indicate that the deposition process is linear and highly reproducible from layer to layer and that a monomolecular film of PM may be obtained in each PDAC/PM bilayer by controlling the adsorption time. Second harmonic generation measurements from the composite films gave a second-order susceptibility χ(2) of 8.1 × 10-9 esu and confirm that the PM fragments are arrayed with a high degree of orientation and acentric polar order in the films. Atomic force microscopy images provided the surface morphology of sequential layers of PDAC and PM fragments. Relative PDAC/PM bilayer thicknesses of 55 Å were observed, and the homogeneity of the layers was found to improve as the number of layers increased.

Holographic surface relief gratings (SRGs) were fabricated on composite films assembled by electrostatic layer-by-layer (ELBL) deposition of a polyelectrolyte, poly(dimethyl diallylammonium chloride) (PDAC), and an azo dye, Congo Red (CR). Surface modulation and first-order diffraction efficiency of the SRG were found to increase with the thickness of the PDAC/CR films. Polarized absorption spectra indicated an oriented growth of CR on the PDAC film. Analysis of the film thickness, FTIR, and FT-Raman results confirmed that the electrostatic attraction between CR and PDAC, as well as the π−π interaction between CR chromophores resulting in the formation of J aggregates, lead to formation of PDAC/CR composite films. Photochemical changes of the PDAC/CR films after irradiation were investigated by UV−vis absorption, FTIR, and FT-Raman spectroscopy. The results indicate that in addition to trans ⇔ cis photoisomerization of CR in the composite film, an irreversible photochemical degradation of CR also simultaneously occurs. Recording SRG on PDAC/CR films by s- and p-polarized beams show different behavior compared to spin-coated films of polymers containing functionalized azo chromophores. Our results indicate that the volume collapse due to the photodegradation of CR in the polymeric matrix, as well as gradient force-induced migration due to trans ⇔ cis isomerization cycling of CR contribute to the formation of SRG on the composite films. This approach provides a methodology to fabricate SRGs for optical information storage applications by using the facile ELBL technique to assemble commercially available azo dyes and polyelectrolytes.

A simple and general method is reported to tune the multicolour output of lanthanide-ion doped NaYF(4) upconversion nanoparticles within a given composition by controlling the reaction temperature in the thermolysis procedure.