Dye-Sensitized Solar Cells Based on Deep Eutectic Solvent Electrolytes: Insights from Experiment and Simulation

Abstract

In the present study, we examined a choline chloride−ethylene glycol (ChCl−EG) deep eutectic solvent (DES) mixed with different iodide salts as electrolytes in dye-sensitized solar cells (DSSCs) by experiment and atomistic molecular dynamics simulations. The photovoltaic performance of DES-based DSSCs revealed that solar cells with an inorganic iodide source show higher performance than cells with an organic iodide source. In this case, the influence of potassium (K + ) and 1-etyl-3-methylimidazolium (Emim + ) counterions on the DSSC performance in DES-based electrolytes was studied. The photovoltaic and electrochemical properties revealed that the presence of KI salt in the electrolyte solution considerably enhances the DSSC efficiency. In this way, the effect of iodide sources on the viscosity, conductivity, and impedance spectra of DES electrolytes was investigated. Additionally, MD simulations of the TiO 2 /DES electrolyte and Pt/DES electrolyte interfaces suggest that K + cations cover the surface of anatase TiO 2 . Furthermore, the dynamics of iodide anions in the KI system was found to be higher than that of K + cations. The diffusion coefficient of K + in the DES was found to be systematically lower compared to that of Emim + due to the higher coordination of K + ions with chloride ions and EG molecules.

Deep Eutectic Solvents in Solar Energy Technologies

“…The interest in DES-based DSSCs has very recently increased, with a number of reports being published in 2021. M. Heydari Dokoohaki and co-workers studied the effect of an inorganic and an organic iodide source (namely KI and 1-ethyl-3-methylimidazolium iodide, EmimI) in a ChCl/EG 1:2 DES, both with an experimental and an atomistic molecular dynamics approach [ 109 ]. The sensitizer was the commercial N719 ( Figure 4 ) and the electrolyte solutions were composed by (i) 0.6 M KI, 0.02 M I 2 ; (ii) 0.6 M EmimI, 0.02 M I 2 ; (iii) 0.3 M KI, 0.3 M EmimI, 0.02 M I 2 .…”

Highly Efficient Dye-Sensitized Solar Cells Based on Electrolyte Solutions Containing Choline Chloride/Ethylene Glycol Deep Eutectic Solvent: Electrolyte Optimization

“…The best DSSC performance in such systems was reported with an efficiency of 6.9% for a binary mixture of CholCl/phenol DES with MeCN (v/v 20:80) . Very recently, we reported on a combined experimental/theoretical (molecular dynamics­(MD) simulations) study on DSSC electrolytes containing CholCl/EG and showed that the presence of KI leads to a better performance than 1-ethyl-3-methylimidazolium iodide (EmimI) (1.6% vs 0.73% power conversion efficiency in a DSSC based on the dye N719 (bis­(tetrabutylammonium) cis -bis­(isothiocyanato)­bis­(4,4′-dicarboxylato-2,2′-bipyridine)­ruthenium­(II)) . The MD simulations showed that the smaller K + cation adsorbed efficiently to the TiO 2 surface and improved the short-circuit photocurrent density ( J sc ), while the larger Emim + cation showed more pronounced dynamics at the TiO 2 anode and moderately enhanced the open-circuit voltage ( V oc ).…”

“…Mixing of traditional solvents, namely, water, ethanol (EtOH), and MeCN with the viscous DES materials in electrolytes for DSSCs has been shown to improve the redox couple diffusion and thus provides a better photovoltaic performance than pure DES . In this contribution, we report on DES-based electrolytes with a maximum conversion efficiency of a DSSC based on the dye N719 of up to 10%thus beating the 1.6% obtained in the previous studyby using very similar components with the exception of lithium iodide (LiI) instead of potassium iodide (KI), mixing of the DES with MeCN, and varying the components of the electrolyte extensively.…”

“…), propylene carbonate, dimethyl formamide, and dimethyl sulfoxide have been varied with the aim of increasing DSSC performance. − Owing to environmental issues and high volatility of these solvents, the search for more ecologically benign (green) solvents has received increasing interest, and quasi-solid electrolytes based on ionic liquids (gel-type) with good photovoltaic performance and long-term stability have been developed. − Very recently, polysiloxane-based poly­(ionic liquid)­s have been used as quasi-solid electrolytes without iodine and showed an excellent efficiency of 8.3% and retained about 84% of efficiency after 26 months . The so-called deep eutectic solvents (DESs) that are characterized by strong hydrogen bond (H bond) formation and generally comprise a H bond acceptor and a H bond donor have also been proposed as sustainable media to replace traditional solvents − including their use in electrolytes for DSSCs. ,,− Studies on electrolytes containing DESs have become increasingly important because of their physical and chemical features such as high ionic conductivity, a broad electrochemical window, and high thermal stability on one side but also low toxicity, low vapor pressure, nonflammability, good biocompatibility, and low production cost on the other side. − …”

Designing of high‐performance dye‐sensitized solar cells by using a new electrolyte based on deep eutectic solvents

“…The highest η (6.9%) has been obtained using a binary mixture of phenol/choline chloride DES and acetonitrile (AN; volume ratio 20:80) 5 . The application of a choline chloride‐based DES (ethylene glycol/choline chloride) mixed with various iodide salts has also been presented by the research group of Zolghadr et al 20 As measured, the maximum η (1.6%) has been achieved using the inorganic iodide source (KI). In the same year, various alkali DESs have been tested by Branco et al 21 As reported, the best η (2.3%) has been obtained for a DES based on potassium iodide and ethylene glycol.…”