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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]

• Control of porphyrin aggregation through axial coordination by N-containing ligands. • Increase in absorption intensity and red-shifting indicates complexation of ligands. • Pentacoordinated ZnP–Py complex showed higher PCE than hexacoordinated complex. • Pentacoordinated ZnP-Py complex shows 28% increase in PCE than non-coordinated ZnP. • Bipyridine complex shows 44% increase in PCE than non-coordinated ZnP. Porphyrin dyes are susceptible to aggregation which may cause lower short-circuit current density affecting its photoelectric conversion efficiency (PCE) in dye-sensitized solar cells. In this paper, we harness the inherent property of metallated porphyrins that it can axially coordinate with compounds containing lone-pair of electrons, such as pyridines, through the back π-bonding. The use of pyridine or bipyridine spacers to suppress aggregation in β -functionalized Zn-tetraphenylporphyrin-based dyes showed improvement of PCEs by 28% and 44% for 4-methylpyridine and 4,4′-bipyridine ligands, respectively. This clearly demonstrates the benefits of the simple but effective method in suppressing dye aggregation thereby increasing its efficiency. [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]

Two spiro-like organic dyes linked at the thiophene bridge (KS-11 and KS-12) together with the original rod-shaped D-π-A configuration (C1) were designed, synthesized, and characterized based on their electronic structure, and determine the photophysical and photovoltaic properties for its application in dye-sensitized solar cells. Compared to C1, the double D-π-A spiro-like configuration, which consists of two separated light-harvesting moieties, was found to be beneficial to photocurrent generation provided that they are separated properly to prevent intramolecular exciton annihilation. This was observed when KS-11, which is linked at the β -position of the thiophene moiety of D-π-A, was compared with KS-12, where the two D-π-A are linked with an additional thiophene using a α - β linkage. The results show that KS-12 produced a 20% and 17% increase in photovoltaic efficiency under simulated AM 1.5G solar irradiation compared to KS-11 and C1, respectively. This increase in photovoltaic performance is credited mostly to the reduction of recombination effects and the increase in the density of states at the semiconductor surface due to high dye loading and better charge-transfer properties. [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]

Abstract: Spectroscopic and theoretical techniques were used to examine the effects of adsorption solvents and electrolyte additives on the photovoltaic performance of dye sensitized solar cells of two β-substituted zinc porphyrin analogues (A1-H and A1-M), where A1-M has an added methyl group at the phenyl ring attached to the meso-position of the porphyrin macrocycle. These results showed that the different solvents used in the sensitization process affects how the dyes are aggregated and how much of the dyes are adsorbed on the semiconductor surface. The highest efficiency of 4.2% (30min soaking time) and 4.0% (1h soaking time) was achieved for A1-H and A1-M analogues, respectively. The hypsochromic shift observed in the UV/Vis spectra of the analogues when THF was used as a solvent was due to the partial deprotonation of the hydrogen at the carboxylic moiety of the analogues induced by the interaction of the THF molecule. Theoretical calculations at the B3LYP/6-31G(d) level of theory indicated that when THF was used as an adsorption solvent, it tends to form six- or five-coordinate complexes causing the dyes to be largely separated when attached to the semiconductor thus lowering the amount of dye. The dye molecular plane of A1-M was 13° closer to the TiO2 surface than A1-H due to steric hindrance introduced by the methyl group. This increases the surface area occupied by the A1-M dye, as indicated by the smaller amount of dye adsorbed on the TiO2 surface. The addition of 4-tert-butylpyridine or the replacement of lithium ions with guanidinium thiocyanate decreased the solar cell efficiency by 12 and 37%, respectively, which was attributed to a decrease in the electron injection processes. [Copyright &y& Elsevier]