In this work, using the density functional theory (DFT) and time-dependent DFT (TD-DFT), we have theoretically studied the electronic structures, quantum reactivity parameters and absorption spectra of the several dyes based on Zn-porphyrin derivatives in the gas phases, methanol (MeOH) and tert-buthanol (t-BuOH). Also, open-circuit photovoltage (V OC), exciton binding energy (EBE), light harvesting efficiency (LHE), the free energy change of regeneration (∆G regen. (d y e)), and the free energy change of electron injection (∆G inject) have been investigated. The studied dyes in the presence of the solvents showed a smaller gap of the highest occupied molecular orbital (HOMO)the lowest unoccupied molecular orbital (LUMO) and lower EBE, a higher intensity and oscillator strength and red shift in the absorption spectra. These changes facilitate the charge transfer (CT) phenomena in the nano-structures of the dyes and improve the solar cell efficiency. Chemical modifications of the dyes by electron donor groups or conjugated system extension, improve the incident photon to current conversion efficiency (IPCE), the energy gap between the LUMO of the dye and the conduction band (CB) of the TiO 2 (eV OC), and the LHE of these dye-sensitized solar cells (DSSCs). Finally, some correlations between the molecular descriptors and solar cell parameters were analyzed.

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In this research, photovoltaic properties of the indoloquinoxaline-based dyes QX22–QX25 as the (D)2-A−π–A structure were investigated dynamically and kinetically. In these structures, two acceptors cyanoacrylic acid and 2-(1,1-dicyanomethylene)­rhodanine, CCRD, and two π-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−π–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/ΔG 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.

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In this work, ten porphyrin derivatives, including free-base zinc-metalised compounds were studied by varying the position of the carboxyl anchoring group and the alkyl substituents length on the remaining three phenyl rings with the aim of the cell efficiency investigation. Theoretical performances of the sensitisers in the dye-sensitised solar cell systems have been discussed by analysis of the optical absorption, the oxidised potential of ground and excited states, light-harvesting efficiency and electron injection efficiency. Due to lower symmetry of free-based porphyrins, they showed broader bands than zinc porphyrins. The second group sensitisers are better than the first one due to the smaller oxidation potential energy, higher open-circuit voltage and light-harvesting efficiency. The influence of long alkyl substituents on the photovoltaic parameters is not perceptible but ortho and meta positions of anchoring group modify the solar cell performance. Finally, some correlations between the quantum reactivity indices and photovoltaic parameters have obtained and discussed.