N heterocyclic compds., such as N-methylbenzimidazole (MBI), are commonly used as additives to electrolytes for dye-sensitized solar cells (DSCs), but the chem. transformation of additives in electrolyte solns. remains poorly understood. Solid cryst. compd. (MBI)6(MBI-H+)2(I-)(I3-) (1) was isolated from different electrolytes for DSCs contg. MBI as additive. The crystal structure of 1 was detd. by single-crystal x-ray diffraction. In the crystal structure, 1 contains neutral and protonated MBI fragments; iodide and triiodide anions form infinite chains along the crystallog. a-axis. The role of the solvent and additives in the crystn. process in electrolytes is discussed.