Relationship between dye–iodine binding and cell voltage in dye‐sensitized solar cells: A quantum‐mechanical look

Abstract

It has been proposed that iodine binding to dyes may actually decrease the cell efficiency of a dye-sensitized solar cell. A previous experimental study showed that a two-atom change from oxygen to sulfur increased recombination of iodine with injected electrons by a factor of approximately 2. Here, it is shown that iodine binding is a plausible explanation for this effect. The steric and conjugation effects are quantified separately using a set of model compounds. Quantum-chemical calculations show that elongation of the hydrocarbon chain has only an insignificant effect on the iodine and bromine binding to the chalcogen atoms (O, S, Se). The conjugation, however, significantly disfavors the iodine and bromine interaction. Iodine and bromine binding to the dye and model compounds containing sulfur is significantly more favorable than to their oxygen containing counterparts. Bromine binding to dyes is shown to be stronger than that of iodine. Accordingly, bromine binding to dyes may contribute significantly to the observed lower efficiencies in cells using Br(3)(-)/Br(-) as the redox couple.

Enhancing the photoresponse by CdSe‐Dye‐TiO2‐based multijunction systems for efficient dye‐sensitized solar cells: A theoretical outlook

“…The extent of interaction of the dye sensitizers with the TiO 2 as well as the interaction of the Dye‐TiO 2 adsorbed system with the CdSe semiconductor ODs was determined in terms of the interaction energy. The interaction energy calculation was carried out using the following relationship: where Δ G r is the interaction energy for the binding of the dye molecule to the (TiO 2 ) 6 cluster as well as the interaction energy of binding (CdSe) 13 semiconductor OD to the Dye‐(TiO 2 ) 6 system. Furthermore, X 2 represents (TiO 2 ) 6 /(CdSe) 13 and the “molecule” represents the dye molecule/Dye‐(TiO 2 ) 6 .…”

Computational studies on optoelectronic and charge transfer properties of some perylene-based donor-π-acceptor systems for dye sensitized solar cell applications

“…The single point energy scan revealed that the P1 and I 2 show maximum interaction at a bond distance of around 2.6 Å (see Supporting Information Figure S3). The interaction energy calculation was carried out using the following relationship: where ΔG r is the interaction energy for the binding of the donor atom to the iodine molecule. Further, in the Equation 2 represents I 2 and the “molecule” represents the molecule containing the donor atom.…”

Intermolecular interactions between a Ru complex and organic dyes in cosensitized solar cells: a computational study

“…A DFT study of I 2 binding with Ru bipyridyl dyes (K19 and TG6) by Asaduzzaman and coworkers supports this hypothesis. 18 Very recently, O'Regan and coworkers rediscovered that dye layer-electrolyte (I 2 ) interaction is more important than the TiO 2 -electrolyte surface in terms of the recombination. 44 Acceleration of recombination, where electrons in TiO 2 are transferred back to the I 2 in the electrolyte, [45][46][47] lowers V oc .…”

“…The intermolecular interaction energy (DG) was determined as the energy difference between the sum of the isolated monomers and the dimer or the complex. 18 With this definition, the smaller (more negative or less positive) the interaction energy, the stronger the intermolecular interaction.…”