TD-DFT investigations on structural modification in Carbazole based
organic Photosensitizers to improve electron injection in DSSC
Abstract
Time-dependent density functional theory approach implemented at
hybrid-B3LYP, GGA-PBE and DFTB levels of theory was used to model
photoinjection in organic-dye/TiO2 quantum-dot to explore the prospects
of improvement of DSSC. The photosensitizer used in this study consisted
of six carbazole based organic dyes having acceptor as cyanoacrilic acid
group and oligothiophene π-bridge spacer. The modifications were made in
the dyes by increasing length of the spacer by adding thiophene and
oxadiazole rings at different positions of the donor-acceptor bridge.
The structural variations appeared to alter the electronic and optical
properties of dyes studied via energy levels and excitation spectra. The
UV-Vis spectra calculated for all the dyes in solvents exhibited a red
shift in spectral peaks with increase in polarity of the solvents. The
findings of the study pointed towards photoinjection of indirect nature
studied in dye-(TiO2)96 complex for six different dyes. The substitution
of oxadiazole ring in center and addition of a thiophene ring at the
edge of the spacer produced two dyes which exhibited lowest injection
energies of 0.11eV and 0.17 eV along with the regeneration energies of
1.18 eV and 1.12 eV respectively. The dyes reported herein may have
promising applications in photoanode for enhancing the performance of
DSSC.