Improved exchange reaction in an ionic liquid electrolyte of a quasi-solid-state dye-sensitized solar cell by using 15-crown-5-functionalized MWCNT

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Abstract
Nanocomposite, 15-crown-5-functionalized multi-wall carbon nanotubes (denoted as MWCNT-15-C-5) were synthesized and used as an additive along with the ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4) in the electrolyte of a dye-sensitized solar cell (DSSC); the pertinent quasi-solid-state DSSC showed a far superior photovoltaic performance than that of a cell with bare EMIBF4 or with MWCNT-added EMIBF4 (MWCNT/EMIBF4). The heterocyclic structure of the crown ether, 15-C-5, provides its cavities to capture the lithium ions (Li+) in a DSSC, thereby facilitating the dissolution of Li+ and I− in the electrolyte of the cell. This further contributes to an improvement in the exchange reaction of I−/I3 − in the electrolyte with EMIBF4. Consequently, the values of short-circuit current density (JSC) and power-conversion efficiency (η) of the DSSC with both EMIBF4 and MWCNT-15-C-5 in its electrolyte showed an increase from 3.23 ± 0.30 to 5.53 ± 0.38 mA cm−2 and from 1.52 ± 0.04 to 2.11 ± 0.10%, respectively, with reference to the values of a DSSC with bare EMIBF4. Moreover, the at-rest durability of this quasi-solid-state DSSC was found to be unfailing for a period of 1200 h at 100 mW cm−2 illumination. Explanations are substantiated with Raman spectra, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HR-TEM), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS).

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