15 research outputs found
Comparative Interface Metrics for Metal-Free Monolayer-Based Dye-Sensitized Solar Cells
The first quantitative comparison between self-assembled
monolayers of homologous carboxylate- and phosphonate-terminated organic
dyes that are of use in dye-sensitized solar cells (DSSCs) is reported.
(Cyanovinyl)Âphosphonate-terminated oligothiophenes and (cyanovinyl)Âcarboxylate-terminated
oligothiophenes were synthesized on TiO<sub>2</sub> thin film electrodes.
Structurally analogous organics were compared for the effect of the
anchoring groups on photochemical properties in solution as measured
by UV/vis spectroscopy and for reactivity with the electrode surface.
Monolayers were grown on the TiO<sub>2</sub> electrodes either by
“tethering by aggregation and growth” (T-BAG) or by
solution dipping. Surface roughness and homogeneity, elemental composition,
and thickness of the monolayers were evaluated by atomic force microscopy
(AFM), X-ray photoelectron spectroscopy (XPS), and ellipsometry. Molecular
loadings for each monolayer on TiO<sub>2</sub> were quantified by
quartz crystal microgravimetry (QCM), and the stability of bonding
between each class of dyes and the TiO<sub>2</sub> was evaluated by
measuring desorption, also by QCM; the carboxylates underwent significant
dissociation in aqueous media but the phosphonates did not. DSSCs
were prepared from each congener and from simple oligothiophene phosphonates
to determine the effect of the cyanovinyl group on device behavior;
all DSSCs were studied under irradiation from a AM 1.5G solar light
source; the effect of cyanovinyl group termination was comparable
to that of adding a thiophene moiety, and the DSSC using a self-assembled
monolayer of (sexithiophene)Âphosphonate (6TP) had total power conversion
efficiency (η) of ca. 5%