Multi‐Dentate Carbazole Based Schiff Base Dyes with Chlorovinylene Group in Spacer for Dye‐Sensitized Solar Cells: A Combined Theoretical and Experimental Study.

Abstract

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.

Prediction of Absorption Spectrum Shifts in Dyes Adsorbed on Titania

“…The conjugated spacers based on vinylene, ethynylene, furan, thiazole, thiophene and other fused aromatic segments (indole 87 , fluorene 88 , benzothiadiazole 89 ) showed similar peak shifts in both directions. Other groups such as diphenylquinoxaline 90 , 1-chlorobuta-1,3-diene 91 , dithienobenzotriazole 92 and dithienobenzofurazan 93 found in a limited number of cases were largely associated with red-shifted peaks. On the other hand, those containing linkers based on fused thiophene derivatives such as dithienopyrrolobenzotriazole 94 , cyclopentadithiophene 95 , thienothienopyrrole 96 , silolodithiophene 97 were blue shifted by more than 50 nm compare to the solution.…”

The improved performance of dye‐sensitized solar cells using co‐sensitization and polymer gel electrolyte

“…The CV was performed in an acetonitrile solution containing 0.1 N tetraethylammonium tetrafluoroborate (TEABF 4 ) at a scan rate of 20 mVs −1 . The CV results revealed that the ground state oxidation potentials ( E ox ) or highest occupied molecular orbital (HOMO) of CDIB (vs. Normal Hydrogen Electrode (NHE)) are observed at 0.827 V (Figure 2) which has significantly more positive than 0.4 V in comparison to the redox potential of the iodide/triiodide pair indicating that oxidized sensitizers can be recycled efficiently 88 . In addition, the intersection of absorption spectra was used to determine the zero‐zero excitation energy (E 0−0 ) and obtained value is 2.857 V (vs. NHE).…”

Carbazole based organic dyes as effective photosensitizers: A comprehensive analysis of their structure‐property relationships

“…As a rule, the areas of electrostatic potential in terms of color increase in the order of blue > green > yellow > orange > red. [ 46–47 ] However, the areas of low potential (red color) and the areas of high potential (blue color) are characterized by abundance and dearth of electrons, respectively. From Figure 6, it is evident that the low potential was observed for all the three dyes on the electron‐accepting carboxylic acid (‐COOH) group, thus indicating the abundance of electrons in the red region of the molecule.…”