Theoretical design and characterization of NIR porphyrin-based sensitizers for applications in dye-sensitized solar cells

New porphyrin-based dyes were designed by modifying the acceptor and donor groups of the champion SM315 dye. The modified acceptor units of the new dyes rendered stronger electron withdrawing ability which resulted in better charge transfer and light harvesting properties with reference to SM315. The acceptor design of K-04 dye, composed of benzothiadiazole and 4-(cyanomethyl)benzoic acid, is the most successful in improving the charge transfer property, evidenced by the highest amount of transferred charge (qCT), charge transfer distance (DCT), and variation of dipole moment (μCT), and the most bathochromically shifted broad Q-band with enhanced molar extinction coefficient. For quantitative estimation of the light harvesting ability of the dyes, the LHE curve and Jscmax were calculated revealing that K-04 dye is the best light harvester among the dyes with varied acceptor unit. Moreover, the highest dipole moment of the dye-TiO2 complex ( μ d y e - T i O 2 ) and largest spatial separation distance (r) between the TiO2 surface and hole centroid of K-04 dye estimates its highest Voc within the group. With respect to K-04, changing the donor group to 9,9-dimethyl-10-phenyl-9,10-dihydroacridine, a semi-rigid triphenylamine (tPA) donor named as D1, resulted in a significant bathochromic shift of the Q-band with a remarkably high molar extinction coefficient. Among the derivatives of D1, the D4 donor group functionalized with diphenylamine enforced the push-pull character resulting in the most favorable CT properties and LHE of K-44 dye. These properties, along with the highest Jscmax, and largest μ d y e - T i O 2 and r, made K-44 dye the most promising candidate in this series.