Dye-sensitized solar cells and complexes between pyridines and iodines. A NMR, IR and DFT study

Interactions between triiodide (I3-) and 4-tert-butylpyridine (4TBP) as postulated in dye-sensitized solar cells (DSC) are investigated by means of 13C NMR and IR spectroscopy supported by DFT calculations. The charge transfer (CT) complex 4TBP·I2 and potential salts such as (4TBP)2I+, I3- were synthesized and characterized by IR and 13C NMR spectroscopy. However, mixing (butyl)4N+, I3- and 4TBP at concentrations comparable to those of the DSC solar cell did not lead to any reaction. Neither CT complexes nor cationic species like (4TBP)2I+ were observed, judging from the 13C NMR spectroscopic evidence. This questions the previously proposed formation of (4TBP)2I+ in DSC cells.

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► Triiodide and pyridines are important electrolyte components in DSCs.
► Complex formation between these species has been previously suggested.
► Observed NMR shifts indicate that no such interaction takes place in CH3CN solution.