DFT/TD-DFT study of novel T shaped phenothiazine-based organic dyes for dye-sensitized solar cells applications

Five novel T shaped phenothiazine-based organic dyes DITP1 similar to 5 with different spacers at N (10) position were designed. The geometries, electronic structures, absorption spectra, electron transfer and injection properties of these isolated dyes and dye/(TiO2)(9) systems were investigated via density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculation. The optimized geometries indicate that these T shaped dyes show non-planar conformations, which are helpful in suppressing the dose intermolecular pi-pi aggregation in device and enhancing thermal stability. The calculated results indicate that type of pi-conjugated spacers can affect the molecular absorption spectra. Introduction of thiophene-benzothiadizole-thiophene unit as pi-conjugated spacer can most effectively shift the light absorption to near infrared region and enhance the light harvesting efficiency (LHE). Moreover, it is found that these dyes show a good performance of electron injection and dye regeneration owing to the proper electron injection driving force (Delta G(inject)) and dye regeneration driving force (Delta G(reg)). The theoretical results reveal that these dyes could be used as potential sensitizers for DSSCs, and DTTP4 would be the most plausible sensitizer for high-efficiency DSSCs due to the narrow HOMO-LUMO energy gap (Delta(H-L)) broad absorption spectrum, high LHE value, and large dipole moment (mu(normal)).(C) 2019 Elsevier B.V. All rights reserved.