The role of the electronic structure and solvent in the dye-sensitized solar cells based on Zn-porphyrins: Theoretical study

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 phase, methanol (MeOH) and tert-buthanol (t-BuOH). Also, open-circuit photovoltage (VOC), exciton binding energy (EBE), light harvesting efficiency (LHE), the free energy change of regeneration (ΔGregen·(dye)), and the free energy change of electron injection (ΔGinject) 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 TiO2 (eVOC), and the LHE of these dye-sensitized solar cells (DSSCs). Finally, some correlations between the molecular descriptors and solar cell parameters were analyzed.