Triphenylamine-based dyes with chloro groups suitably placed on their π-linkers affect DSSC efficiency.

Substitution at the 4-position of coumarin alters the photophysical, electrochemical and photovoltaic properties of the dyes.

Four new metal free organic Schiff bases employing N-hexyl/Nphenyl carbazole moiety as a donor, 1-chlorobuta-1,3-diene as a π-bridge and 4-amino salicylic acid as an anchor, are designed, synthesized and investigated as photosensitizers in the dye-sensitized solar cell (DSSC). We have studied the combined effect of the introduction of electronegative chlorine group with an additional double bond in π-conjugation and 4amino salicylic acid as a tridentate anchoring group, on the optoelectronic, theoretical and photovoltaic performance of the dyes. The halogen electronegativity and strong polarization of the C-X bond represented interesting acceptor moieties for organic push-pull systems. The designed strategy leads to redshifted absorption maxima and reduced band gap. Density functional theory (DFT) and Time dependent density functional theory (TD-DFT) are used to support the performance of the obtained carbazole based Schiff-base dyes. When compared with the other three dyes, 3b exhibited the smallest band gap (2.86 eV), red-shifted absorption spectra on TiO 2 surface (453 nm) and improved nonlinear optical (NLO) properties. Among the four reported dyes, 3b exhibited the excellent photovoltaic performance, short-circuit current density (J sc ) of 10.60 mA/cm 2 , open-circuit voltage (V oc ) of 0.626 V and fill factor (FF) of 70.0 %, conforming to a total power conversion efficiency of 4.3% under 1 sun light illumination due to the presence of two anchoring groups with multiple binding sites on TiO 2 surface leading to efficient charge injection. NLO properties are examined theoretically and dye 3b exhibited the highest value of the first hyperpolarizability (β) amongst all four dyes which are in good agreement with exhibited highest DSSC efficiency. The present work revealed that the incorporation of electronegative chlorine group in π-conjugation and the use of double acceptors with multiple binding sites for better adsorption on TiO 2 surface are crucial to supplement the efficiency of the dye.

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