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• New NIR-dyes were designed based on the champion SM315 dye. • 4-(Cyanomethyl)benzoic acid is a promising acceptor group for NIR porphyrin dyes. • The semi-rigid tPa donor brought notable red-shift and increased molar absorptivity. • The designed dyes exhibit excellent CT character and LHE, and high J sc max and V oc. 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 (q CT), charge transfer distance (D CT), and variation of dipole moment (μ CT), 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 J sc max 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-TiO 2 complex (μ d y e - T i O 2 ) and largest spatial separation distance (r) between the TiO 2 surface and hole centroid of K-04 dye estimates its highest V oc 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 J sc max, and largest μ d y e - T i O 2 and r , made K-44 dye the most promising candidate in this series. [ABSTRACT FROM AUTHOR]

Abstract Four novel dyes featuring new semi-rigid triphenylamine donor groups have been synthesized and successfully employed as sensitizers in dye-sensitized solar cells (DSSCs). Opting for the new semi-rigid triphenylamine (tPA) electron-donating unit yielded a better V oc and J sc resulting to a power conversion efficiency (PCE) which is 16% higher compared to a reference dye whose electron-donating group is a conventional tPA unit. Density functional theory (DFT) and time-dependent DFT calculations revealed the more favorable charge-transport properties of the dye based on the new semi-rigid donor unit. Among the synthesized dyes, the DSSC device based on Dhkx-4 dye in conjunction with iodine-based electrolyte achieved a PCE of 6.23%, with V oc of 0.661 V, J sc of 13.31 mAcm−2, and FF of 0.71 under simulated AM 1.5 G condition. Therefore, the novel semi-rigid tPA donor unit presented in this work is a promising donor group for a sensitizer in DSSCs and systematic structural engineering of the presented designs could offer valuable contributions for the development of the photovoltaic devices. Graphical abstract Image 1 Highlights • D-π-A dyes based on a new semi-rigid triphenylamine donor were synthesized for DSSCs. • The new Dhkx-1 dye attained a PCE that is 16% higher than the L1 reference dye. • The experimental data are interpreted well by the results of DFT/TD-DFT calculation. • The solar cell device based on a simple Dhkx-4 dye attained the highest PCE of 6.23%. [ABSTRACT FROM AUTHOR]

The use of theoretical techniques in the structural development of dye-sensitized solar cells helps in the efficient screening of the dyes. To properly rationalize the dye’s design process, benchmark calculations were conducted using long-range corrected exchange–correlation (xc) functionals with varying separation parameters to be able to predict the excited-state energies of triphenylamine-based dyes, namely: PPS, PSP, and PSS, wherein they differ at the π-conjugated bridge using thiophene and/or phenyl moieties. The results show that LC- ω PBE xc functional with an optimized parameter provided better correlation with the experimental results compared to the other functionals. The relative shifts of the absorption spectra, light harvesting efficiency, normal dipole moments, as well as the ionization potentials and electron affinities of the dyes were well-correlated with the experimental data. A new set of dyes was designed in an effort to increase its solar cell efficiency that was patterned after PSS with an additional donor moiety such as fluorene, cyclopentaindole, and pyrene attached asymmetrically at the triphenylamine ring. Among the newly designed dyes, analogs that contain 4-phenyl-1,2,3,4-tetrahydrocyclopenta[ b ]indole (I) and pyrido[2,3,4-5- imn ]phenanthridine-5,10(4 H ,9 H )-dione (P2) as the additional donor moiety produced the best photophysical properties and charge-transfer characteristics for a promising dye for solar cell applications. [ABSTRACT FROM AUTHOR]