The role of silanized and capped with TiO2 gold nanorods of different aspect ratios in co-sensitized DSSCs for transparent windows applications

Gold nanarods (GNRs) with an aspect ratio equal to 3:1 and 4:1 and a major axis equal to 50 nm, silanized and capped with titania (c-GNRs), were embedded within the 6? thick semiconductor layer of DSSCs based on an organic D-?-A sensitizer dye (L0 or L1) and a squaraine co-sensitizer (SQ2). These dye cocktails and a transparent titania paste were selected to maximize the transmittance of DSSCs in a region of maximum visual acuity. The thickness of the SiO2 layer was consisted of about 4.0 nm and that of the TiO2 layer of about 2.0 nm in order to maintain high the localized surface plasmon resonance (SPR) effects produced by GNRs and to prevent Au corrosion. The slight thickness of both types of capping was not sufficient to preserve the dimensions of the gold nanorods during sintering at 450 °C. Absorbance, transmittance and reflectance spectra of the films were measured after they were dyed. The plasmonic effects were distinguishable both in absorbance and absorptance spectra for all the types of dyes cocktails and GNRs aspect ratios used. Transmittance values depended on the cocktail used and on the adsorption of the dyes on the semiconductor film blended with c-GNRs. When the mix of L1 and SQ2 was used together with GNRs of a 3:1 aspect ratio, we achieved an increase of 23% in DSSC efficiency (from 3.50% to 4.32%) but transmittance values higher than 50% only between 560 nm and 630 nm.