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

The intermolecular interactions of a cyclometallated Ru-complex dye (I) and a diketopyrrolopyrrole-based organic dye (2) with iodine species (I-3(-), I-2, and I-2(-center dot)) 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(-center dot) interaction also involves I I bond dissociation by single-electron transfer from the reduced dye to I-2(-center dot) to form a [I- ... Dye ...I-] complex. In most of the reduced dye-I-2 complexes, single-electron transfer from the dye ton 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(-center dot) and I-, by I-2 via the [Dye ... I-2(-)] complex yielding If., or by I-2(-center dot) via the [I- ... Dye ... I-] complex yielding two I-. (C) 2018 Elsevier B.V. All rights reserved.