Ab Initio Determination of Ground and Excited State Oxidation Potentials of Organic Chromophores for Dye-Sensitized Solar Cells

Ab initio calculations of the ground state oxidation potential (GSOP) and excited state oxidation potential (ESOP) are reported for a set of four triphenylamine-based dyes for dye-sensitized solar cell (DSSC) applications, with increasing degree of charge transfer. The performance of DFT in predicting GSOP is evaluated by employing various exchange-correlation (x-c) functionals, with different amounts of Hartree-Fock exchange and different combinations of correlation functionals. The choice of the correlation part of the x-c functional was crucial in getting accurate GSOPs. For excited state geometry optimizations, needed to calculate the adiabatic excitation energies E0-0 and therefore the ESOPs, the use of hybrid functionals with a large amount (50%) of nonlocal Hartree-Fock exchange has been shown to be mandatory to avoid the formation of artificial minima in correspondence of a twisted geometries with a high degree of charge transfer. Our results show that a proper DFT/TDDFT approach can provide a reliable description, within 0.2-0.3 eV, of both GSOP and ESOP compared to experimental values for dyes of relevant interest for the DSSCs technology. This paves the way, along with the absorption spectra simulation, to the efficient computational screening of new dyes for DSSC devices.