Electrolyte Tuning in Iron(II)-Based Dye-Sensitized Solar Cells: Different Ionic Liquids and I2 Concentrations.

Mariia Becker,Edwin C Constable,Catherine E Housecroft

doi:10.3390/ma14113053

Abstract

The effects of different I2 concentrations and different ionic liquids (ILs) in the electrolyte on the performances of dye-sensitized solar cells (DSCs) containing an iron(II) N-heterocyclic carbene dye and containing the I–/I3– redox shuttle have been investigated. Either no I2 was added to the electrolyte, or the initial I2 concentrations were 0.02, 0.05, 0.10, and 0.20 M. The short-circuit current density (JSC), open-circuit voltage (VOC), and the fill factor (ff) were influenced by changes in the I2 concentration for all the ILs. For 1-hexyl-3-methylimidazole iodide (HMII), low VOC and low ff values led to poor DSC performances. Electrochemical impedance spectroscopy (EIS) showed the causes to be increased electrolyte diffusion resistance and charge transfer resistance at the counter electrode. DSCs containing 1,3-dimethylimidazole iodide (DMII) and 1-ethyl-3-methylimidazole iodide (EMII) showed the highest JSC values when 0.10 M I2 was present initially. Short alkyl substituents (Me and Et) were more beneficial than longer chains. The lowest values of the transport resistance in the photoanode semiconductor were found for DMII, EMII, and 1-propyl-2,3-dimethylimidazole iodide (PDMII) when no I2 was added to the initial electrolyte, or when [I2] was less than 0.05 M. Higher [I2] led to decreases in the diffusion resistance in the electrolyte and the counter electrode resistance. The electron lifetime and diffusion length depended upon the [I2]. Overall, DMII was the most beneficial IL. A combination of DMII and 0.1 M I2 in the electrolyte produced the best performing DSCs with an average maximum photoconversion efficiency of 0.65% for a series of fully-masked cells.

Highlights

We have previously shown that an electrolyte composed of LiI (0.18 M), I2 (0.05 M), and the ionic liquids (ILs) 1-propyl-2,3-dimethylimidazolium iodide (PDMII, Scheme 1, 0.60 M) in methoxypropionitrile (MPN) led to a photoconversion efficiency of up to 0.66% for fully masked dye-sensitized solar cells (DSCs) [25]
We have shown that the structure of the IL strongly influprevious investigations, we have shown that the structure of the ILdye strongly encesInthe photoconversion efficiency of DSCs sensitized with the iron(II)
In the first part of the investigation, DSCs sensitized with 1 in the presence of the coadsorbant cheno were fabricated with electrolytes that differed in the ionic liquid present

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Sustainable approaches to energy generation are of critical societal importance and are one of the United Nations Sustainable Development Goals (SDG7) [1]. The conversion of solar to electrical energy is a critical sustainable goal, and an alternative strategy to the well-established silicon photovoltaics is seen in the development of dye-sensitized solar cells (DSCs) [2]. An n-type DSC (Figure 1) employs a wide-bandgap n-type semiconductor, typically TiO2 (anatase), with a sensitizer adsorbed on the surface to extend the absorption of light into the visible region [3,4,5,6]. Sensitizers in DSCs are typically metal-free (organic) or ruthenium(II)-based dyes. State-of-the-art ruthenium dyes reach up to ca. State-of-the-art ruthenium dyes reach up to ca. 12%

Methods

Results

Conclusion