Abstract
We demonstrate that the performances of dye-sensitized solar cells (DSCs) sensitized with a previously reported N-heterocyclic carbene iron(II) dye in the presence of chenodeoxycholic acid co-adsorbant, can be considerably improved by altering the composition of the electrolyte while retaining an I−/I3− redox shuttle. Critical factors are the solvent, presence of ionic liquid, and the use of the additives 1-methylbenzimidazole (MBI) and 4-tert-butylpyridine (TBP). For the electrolyte solvent, 3-methoxypropionitrile (MPN) is preferable to acetonitrile, leading to a higher short-circuit current density (JSC) with little change in the open-circuit voltage (VOC). For electrolytes containing MPN, an ionic liquid and MBI (0.5 M), DSC performance depended on the ionic liquid with 1-ethyl-3-methylimidazolium hexafluoridophosphate (EMIMPF) > 1,2-dimethyl-3-propylimidazolium iodide (DMPII) > 1-butyl-3-methylimidazolium iodide (BMII) ≈ 1-butyl-3-methylimidazolium hexafluoridophosphate (BMIMPF). Omitting the MBI leads to a significant improvement in JSC when the ionic liquid is DMPII, BMII or BMIMPF, but with EMIMPF the removal of the MBI additive results in a dramatic decrease in VOC (542 to 42 mV). For electrolytes containing MPN and DMPII, the effects of altering the MBI concentration have also been investigated. Although the addition of TBP improves VOC, it causes significant decreases in JSC. The best performing DSCs with the NHC-iron(II) dye employ an I−/I3−-based electrolyte with MPN as solvent, DMPII ionic liquid (0.6 M) with no or 0.01 M MBI; values of JSC = 2.31 to 2.78 mA cm−2, VOC = 292 to 374 mV have been achieved giving η in the range of 0.47 to 0.57% which represents 7.8 to 9.3% relative to an N719 reference DSC set at 100%. Electrochemical impedance spectroscopy has been used to understand the role of the MBI additive in the electrolytes.
Highlights
The field of dye sensitized solar cells (DSCs) has developed significantly [1,2,3] since the pioneering publication of O’Regan and Grätzel [4]
The best performing DSCs with the N-heterocyclic carbene (NHC)-iron(II) dye employ an I−/I3−-based electrolyte with MPN as solvent, dimethyl-3-propylimidazolium iodide (DMPII) ionic liquid (0.6 M) with no or 0.01 M MBI; values of JSC = 2.31 to 2.78 mA cm−2, VOC = 292 to 374 mV have been achieved giving η in the range of 0.47 to 0.57% which represents 7.8 to 9.3% relative to an N719 reference DSC set at 100%
We have shown that the performances of DSCs sensitized with the NHC iron(II) dye 1 originally reported by Gros and co-workers [34], can be significantly enhanced by tuning of the electrolyte composition, while retaining an I−/I3− redox shuttle
Summary
The field of dye sensitized solar cells (DSCs) has developed significantly [1,2,3] since the pioneering publication of O’Regan and Grätzel [4]. The best performing DSCs with the NHC-iron(II) dye employ an I−/I3−-based electrolyte with MPN as solvent, DMPII ionic liquid (0.6 M) with no or 0.01 M MBI; values of JSC = 2.31 to 2.78 mA cm−2, VOC = 292 to 374 mV have been achieved giving η in the range of 0.47 to 0.57% which represents 7.8 to 9.3% relative to an N719 reference DSC set at 100%. The performance parameters and J–V curves for DSCs sensitized with the NHC iron(II) dye 1 and containing electrolytes E1, E1a, E2 and E2a are shown in Table 2 and Figure 1.
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