Interaction between dyes and iodide mediators in p-type dye-sensitized solar cells

Abstract The intermolecular interactions of a cyclometallated Ru-complex dye ( 1 ) and a diketopyrrolopyrrole-based organic dye ( 2 ) with iodine species (I 3 − , I 2 , and I 2 − ) were investigated using density functional theory. The reduced dyes mainly interact with I 3 − via the reductive cleavage of the I I bond, thus forming [I 2 − ⋯Dye⋯I − ]. The I 2 − interaction also involves I I bond dissociation by single-electron transfer from the reduced dye to I 2 − to form a [I − ⋯Dye⋯I − ] complex. In most of the reduced dye–I 2 complexes, single-electron transfer from the dye to I 2 occurs without I I bond breakage, thus forming [Dye⋯I 2 − ]. These results suggest that both 1 and 2 can be completely regenerated in p-type dye-sensitized solar cells (DSSCs). The regeneration process involves one-electron transfer with an iodide–triiodide redox couple via three different mechanisms: by I 3 − via the transient intermediate [I 2 − ⋯Dye⋯I − ] complex yielding I 2 − and I − , by I 2 via the [Dye⋯I 2 − ] complex yielding I 2 − , or by I 2 − via the [I − ⋯Dye⋯I − ] complex yielding two I − .