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The efficacy of dipyridyl and diphenylamine sensitizers in dyesensitized solar cells (DSSCs) is linked to trends in DFT-based charge transfer and non-linear optical (NLO) properties. We chose DFT and Time-dependent-DFT methods. The planarity is improved by replacing the phenyl ring at the donor site with a thiophene ring. Similarly, cyanoacetic acid acceptor improves planarity over rhodamine-3-acetic acid acceptor. In all cases in HOMO, the electron density is located at the donor and some part of the spacer, and in LUMO, it is shifted to the acceptor. Bond length alternation, bond order alternation, quinoid character, effective charge transferred distance, effective charge transferred, chemical potential, electrophilicity index, and electron correlation descriptors showed direct relation, while hardness and hyperhardness showed an inverse relation with NLO properties. We observed higher β 0 and γ for thiophenebased sensitizers ranging from 248.81 × 10 À 30 to 440.92 × 10 À 30 esu and 777.82 × 10 À 36 to 1442.69 × 10 À 36 esu, respectively. Likewise, more negative values of ΔGinject (À 0.630 to À 0.752 eV), a smaller value of ΔGreg (0.662 to 0.790 eV), and higher LHE (0.959 to 0.976) are observed for thiophene-based sensitizers. Also, thiophene-based sensitizers showed shorter TiÀ O bond lengths than their phenyl-based sensitizers. Photovoltaic parameters are directly related to DSSC efficiency and NLO properties.

Modification of a triarylamine donor group along with variation in the anchoring groups could finely manipulate the photophysical property and tuning the behaviour of D–A′–π–A sensitizers in DSSCs for better efficiency achievement.

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Functional group and position isomers of azo and azomethine were selected to investigate their effect on linear and NLO properties. The azo and azomethine analogs show absorption maxima in the range 460–500 nm and 375–435 nm respectively. They are emissive in green, orange to the deep red region with a large Stokes shift of 100–200 nm. When we compared azo and azomethine chromophores i. e. functional group isomers, azo chromophore shows a bathochromic shift of 50–103 nm, while in case of position isomers azo and azomethine having larger conjugation effect i. e. VA‐2 and VI‐2 show a more bathochromic shift of 28 nm and 42 nm than the corresponding analogs VA‐1 and VI‐1, which show respectively 466 nm and 379 nm. Band gaps evaluated by electrochemical method and DFT method are correlated with the bathochromic shift in absorption maxima. The dyes are thermally stable (up to 280 °C). Open and closed aperture Z‐scan techniques were used to evaluate the third order non‐linear optical (NLO) parameters ‐ nonlinear absorptive coefficient (β), nonlinear refractive index (η2), and third order non‐linear optical susceptibility (χ (3)). NLO properties were theoretically calculated by using DFT method with six different functionals. Mean absolute error (MAE) and standard deviation (SD) were evaluated to get more insight into theoretical calculation. With the set of calculated data points, MAE and SD calculated to check performance of the DFT functional. Different functionals were used to evaluate vertical excitation values and compared it with experimental absorption maxima.

Four donor‐pi‐acceptor (D‐π‐A) type sensitizers containing coumarin as the donor unit and cyanoacrylic acid as the acceptor unit are investigated using density functional theory (DFT) and time‐dependent‐DFT methods. The effect of introducing auxiliary acceptor like benzothiadiazole and spacer bridge like 3,4‐ethylenedioxythiophene (EDOT) is analyzed. The EDOT bridge leads to increase in band gap whereas the introduction of benzothiadiazole lessens the band gap. The frontier molecular orbital diagram also shows an efficient intramolecular charge transfer for non‐EDOT based sensitizers. For benzothiadiazole‐based sensitizers, the electrophilicity index was higher and hyperhardness was lower in the estimated reactivity descriptors. The experimentally determined light harvesting efficiency (LHE) of the sensitizers is correlated with the calculated global descriptors. A direct relation of LHE is obtained with electrophilicity index and an inverse relation for hyperhardness. A reverse trend is seen on comparing these descriptors with the band gap of the sensitizers. The computed non‐linear optical (NLO) characteristics show that the benzothiadiazole acceptor increases NLO response, while EDOT‐based sensitizers show a reduced NLO response. The NLO properties also give a direct relation with the LHE and electrophilicity index. The hyperpolarizability exhibits an inverse relation with the transition energy which is in accordance with the Ouder's model.