Anchoring Group and a pi-Spacer Effects on the Dynamics and Kinetics of the Photovoltaic Processes in the Quinoxaline-Based Organic Dye-Sensitized Solar Cells

In this research, photovoltaic properties of the indoloquinoxaline-based dyes QX22-QX25 as the (D)(2)-A-pi-A structure were investigated dynamically and kinetically. In these structures, two acceptors cyanoacrylic acid and 2-(1,1-dicyanomethylene)rhodanine, CCRD, and two pi-spacers furan and thiophene have been used. Density functional theory (DFT), time-dependent DFT (TD-DFT), and natural bond orbital (NBO) were used to evaluate the electronic structures and excited state properties of these metal-free organic dyes. The analysis of the dynamics/kinetics of the photovoltaic parameters of the corresponding dye-sensitized solar cells (DSSCs) shows that each moiety of the D-pi-A system has a more specific effect on one of the photovoltaic properties. On the basis of the obtained results, linear correlations of the incident photon to current conversion efficiency (IPCE) to the k(inj)/Delta G(inj) are stronger than that of light harvesting efficiency (LHE). Moreover, a red shift in the absorption spectra and a higher LHE in the DCRD-based dyes are observed. Although thiophene-based dyes showed an improved exciton dissociation rate, R-d, QX22 and QX23 are the preferred candidates to be applied in solar cells due to their optimized quantum chemistry properties and maximum IPCE.