Proton-coupled electron transfer in dye-sensitized solar cells: a theoretical perspective

The functionality of the proton-coupled electron transfer (PCET) model was tested on a squaraine-sensitized solar cell. The geometrical parameters, excitations, and electronic structures of free and Ti+4-bound squaraine dye were monitored using a set of pure and hybrid density functional theory (DFT) functionals with diffuse and polarization functions. The infrared spectra showed the dye-metal proton transfer. The UV-Vis spectra of unbound and bound squaraine dye using the pure functional (PBEPBE) are in excellent agreement with the experimental ones. The first photoexcited state charge transfer enhanced the charge density around the anchoring group of neat and bound squaraine dye. The injection of electronic charge into the titanium complex was confirmed by density of states (DOS) and natural bond orbital (NBO) analyses. The comparatively high total hyperpolarizability of the squaraine dye is indicative of a potent nonlinear optical (NLO) devise.