Understanding the regeneration mechanism of an oxidized dye with redox couples is significant in improving the efficiency of dye-sensitized solar cells (DSSCs). However, all the previously considered regeneration mechanisms are failed to match the incident photon-to-current efficiency (IPCE) and the UV-vis absorption spectra. Herein, we propose a new regeneration mechanism for organic dyes by assuming the probability of two electron injection from the stable dye-iodide intermediate complex. Thus, the stability and optoelectronic properties of the dye-iodide intermediate complexes of our elementary steps for the regeneration mechanism have been systematically investigated using density functional theory (DFT) and time-dependent (TD)-DFT calculations. Our results highlight the possibility of two electron injection into the semiconductor surface during dye regeneration mechanism, rather than the conventional one electron injection. In addition, the calculated UV-vis absorption spectra for the considered intermediate complexes clearly indicate blue/redshift (see Fig. 1) compared to that of isolated dye, which reflects the IPCE spectra.

Keywords: Dye regeneration mechanism; Organic dye; Electron injection; Dye-sensitized solar cells; Density Functional Theory; UV-vis spectra