Jin-An He

ELECTROSPUN PHOTOVOLTAIC CELLS

ABSTRACT Electrospinning is a simple technique to form high surface area membranes using large static electric potentials. An application, taking advantage of such a high surface area, is a dye-sensitized photovoltaic cell, wherein a chromophore molecule absorbs light before being oxidized to generate a photocurrent. We report functioning photovoltaic cells made from polyacrylonitrile fibers infused with the azo-dye, Congo Red in a liquid-junction cell assembly. Cell performance of the electrospun cells compared favorably to cells made by spin-coating thin films of polyacrylonitrile and Congo Red. Also reported are the effects of adding nanoparticles of titanium dioxide to the cells. Finally, the maximum amount of dye that can be incorporated into a fiber is presented.

Surface relief gratings from electrostatically layered azo dye films

Surface relief gratings (SRGs) were fabricated on composite films assembled by alternate electrostatic deposition of a polyelectrolyte, poly(dimethyldiallylammonium chloride), and an organic azo dye, congo red. The modulation of SRGs was found to increase with the thickness of the matrix films. Significant photochemical bleaching of the azo dye in the polymeric microenvironment as well as gradient-force-induced migration of the small azo dye contributes to the formation of the SRG structure. This finding demonstrates a facile method to fabricate SRGs for optical and information storage applications using commercially available azo dyes and polyelectrolytes.

Mechanisms of surface-relief gratings formation in layer-by-layer films from azodyes

Surface-relief gratings are photoinscribed on ionically adsorbed layer-by-layer (LBL) films of an azodye, Brilliant Yellow (BY), which was layered alternately with a polyelectrolyte. Photoinscription is performed by impinging an interference pattern of p- or s-polarized laser light with moderate intensity onto the LBL film, which is unlikely to cause thermal effects. Large-scale mass transport occurs due to the force associated with the field gradient of the light pattern. The ionic interactions between adjacent layers appear to provide the means for the chromophores to drag the polymer chains upon photoizomerization. LBL films were produced from two different polyelectrolytes and under two distinct pH values leading to markedly different film properties especially concerning photodegradation. Exposure to the laser light, for instance, leads to higher photodegradation in the poly(dimethyl diallylammonium chloride)/BY system, in comparison to the poly(allylamine hydrochloride)/BY films. Mass transport in the latter case is predominantly light-driven, which is consistent with the higher amplitude of modulation for p-polarized light (70 nm) compared to that caused by s-polarized light (18 nm).

Raman Microscopy and Mapping as a Probe for Photodegradation in Surface Relief Gratings Recorded on Layer-by-Layer Films of Congo Red/Polyelectrolyte

Raman microscopy, mapping, and surface-enhanced Raman scattering techniques have been applied to investigate the degradation of Congo Red (CR) in a surface relief grating (SRG) recorded on an electrostatically assembled layer-by-layer film of CR alternated with poly(dimethyl diallylammonium chloride) (PDAC). Photoinduced degradation was suggested by a decrease in the Raman bands assigned to CR with a concomitant increase in the background signal. More degradation was observed in the valleys of the SRG, which corresponded to the most illuminated areas. In a line mapping across the SRG, the Raman intensity of CR bands follows the modulation of the grating, which indicates that photodegradation of CR contributes at least partially to the SRG formation. Surface-enhanced resonance Raman scattering (SERRS) indicates that the phenyl ring groups are located at the film surface. Mapping of the Raman signal over many periods of SRG shows that, within the limits of detection, the chromophores appear to be oriented in much the same way throughout the film. They have no preferred orientation in the peaks and valleys of the SRG after the recording process has been completed.

Synthesis and Characterization of a Ruthenium(II) Complex for Photovoltaic Cells

We have designed and synthesized a new ruthenium complex, [(5‐amino‐1,10‐phenanthroline)bis(4,4′‐dicarboxylic acid‐2,2′‐bipyridine)]ruthenium(II) by introducing two types of ligands, 5‐amino‐1,10‐phenanthroline and 4,4′‐dicarboxylic acid‐2,2′‐bipyridine. We investigated the electronic, spectroscopic, electrochemical, and photovoltaic properties of the Ru(II) complex. The short‐circuit current density and overall solar‐to‐electric energy conversion efficiency of photovoltaic cells made with this Ru(II) complex were found to be 8.9 mA/cm2 and 2.1%, respectively. A series of analogous Ru(II) complexes have also been synthesized and investigated to compare the effects of functional groups on various ligands. HOMO‐LUMO energies and molecular orbital surfaces have been investigated using semiempirical quantum chemical methods.

Study of a poly-1,6-dicarbazolyl-2,4-hexadiyne nanocrystal film by the fifth-order electroabsorption spectroscopy

Electroabsorption spectroscopy is used to investigate the fifth-order nonlinear optical property of a polydiacetylene poly-1,6-dicarbazolyl-2,4-hexadiyne [poly(DCHD)] nanocrystal film assembled by sequential ionic adsorption. The fifth-order susceptibility spectrum clearly identifies the vibrational states, i.e., the double bond and triple bond stretching, which are not resolved in the linear absorption spectrum. These vibrational energies are consistent with those obtained from poly(DCHD) bulk crystal through Raman and electroreflectance spectroscopy at low temperatures. The contributions from the vibrational states are also included in the expressions of hyperpolarizabilities for the electro-optical process. The fit of the experimental data shows excellent agreement between the model and the experiment.