Influence of Solvent on Dye‐Sensitized Solar Cell Efficiency: What is so Special About Acetonitrile?

Abstract

The selection of solvent for preparing a working electrode (and to act as the electrolyte) is known to influence the efficiency of dye‐sensitized solar cells. In this topical review, results taken from a systematic study are presented from the authors’ own lab examining how protic and aprotic solvents, as well as solvent polarity, affect adsorption of carboxylic dyes on the titanium dioxide nanoparticle surface and electron injection from the dye to the semiconductor. Adsorption of dye molecules on nanoparticle surfaces is measured through second harmonic light scattering and electron injection through ultrafast transient mid‐infrared absorption. It is revealed that protic solvents do not allow direct adsorption of the dye onto the semiconductor surface, due to hydrogen bonding with the dye and competitive binding to the semiconductor surface. Aprotic solvents, on the other hand, support solvation of the dye molecules but also facilitate dye adsorption on the semiconductor nanoparticle. Among aprotic solvents, it is found that solvents with higher polarity result in larger adsorption free energy for the dye and faster electron injection. Overall, these studies reveal that aprotic solvents with high solvent polarity (such as acetonitrile) yield more efficient solar cell devices.

Quantitative Modeling of Electron Dynamics and the Effect of Diffusion in Photosensitized Semiconductor Nanocomposites

“…In our recent work, it was observed that flat Ag nanoplatelets acting as photosensitizers on TiO 2 nanorods (77% anatase phase, 23% rutile phase) exhibit enhanced photocatalytic efficiencies compared to spherical Ag nanoparticles . To understand the origin of this enhanced efficiency, TA spectroscopy (probed at 1900 cm –1 (0.24 eV), pumped at 400 nm (3.1 eV)) , was applied to investigate the electron dynamics in this nanocomposite . As depicted in Figure (inset), the rise of the TA signal, corresponding to the electron injection process, was fit to a single exponential rise function convoluted with the IRF (a Gaussian with a fwhm of 300 ± 10 fs). , The rise time was determined to be 13.1 ± 1.5 fs, which is comparable to the ∼15 fs previously measured for much smaller Ag nanoparticles by Lian and co-workers .…”

Solvent-Dependent Functional Aggregates of Unsymmetrical Squaraine Dyes on TiO2 Surface for Dye-Sensitized Solar Cells

“…The dielectric constant values of solvents change the sensitizing ability of the dyes, which results in different aggregated structures and DSSC efficiencies. , A ruthenium-based N3 dye showed high J SC and low V OC values in acetonitrile and low J SC and high V OC values in a dimethyl sulfoxide sensitizing solvent, due to a change in the TiO 2 conduction band (CB) position and interfacial electron transfer from the dye to TiO 2 . A black dye showed significant changes in device efficiencies with a single solvent and with varying concentrations of two solvents . The Z907 dye showed different device efficiencies when the dye was sensitized into the two or more mixed solvents .…”

“…46 A black dye showed significant changes in device efficiencies with a single solvent and with varying concentrations of two solvents. 44 The Z907 dye showed different device efficiencies when the dye was sensitized into the two or more mixed solvents. 47 With changes in adsorption conditions by changing the sensitizing solvent to either single or mixed solvents and changing the adsorption time, porphyrin dyes showed changes in J SC , V OC , and device efficiencies.…”

“…The solvent systems used during the sensitization of dyes on the surface of TiO 2 play a tremendous role in achieving better J SC , V OC , and device efficiency aside from sensitizers, electrolytes, and counter electrodes. − It is known that solvent–surface interaction controls dye-anchoring modes, which are greatly modulated by the protic and aprotic nature of the sensitizing solvents . The dielectric constant values of solvents change the sensitizing ability of the dyes, which results in different aggregated structures and DSSC efficiencies. , A ruthenium-based N3 dye showed high J SC and low V OC values in acetonitrile and low J SC and high V OC values in a dimethyl sulfoxide sensitizing solvent, due to a change in the TiO 2 conduction band (CB) position and interfacial electron transfer from the dye to TiO 2 .…”

Aqueous Biphasic Dye‐Sensitized Photosynthesis Cells for TEMPO‐Based Oxidation of Glycerol

“…[21,22] The prerequisites for glycerol conversion causes stability issues at the photoanode as the ubiquitously employed carboxylic acid-the best performing anchoring group for dyes to metal oxides-is prone to cleavage under aqueous alkaline conditions leading to dye desorption. [23,24] More importantly, the photovoltaic properties in aqueous dye-sensitized systems typically compare poorly with systems using an organic solvent like acetonitrile, [25] incurring losses in power conversion efficiency, lower injection efficiency and shifts of conduction band levels. [24] To make the DSPEC compatible with alkaline aqueous phase conditions required for glycerol oxidation, we envision a biphasic DSPEC system in which the photoanode is protected by an organic phase gel layer.…”