The time‐dependent density functional theory approach, implemented at hybrid‐B3LYP, GGA‐PBE, and density functional‐based tight binding levels of theory, was used to model photoinjection in organic dye/TiO2 quantum dot to explore the prospects of improvement of dye‐sensitized solar cell (DSSC). The photosensitizer used in this study consisted of six carbazole‐based organic dyes, a cyanoacrylic acid group as an acceptor and an oligothiophene π‐bridge spacer. The modifications were made in the dyes by increasing the 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 an increase in the polarity of the solvents. The findings of the study pointed toward the indirect photoinjection of the dye‐(TiO2)96 complex for six different dyes. The substitution of the oxadiazole ring at the center and addition of a thiophene ring at the edge of the spacer produced two dyes that exhibited the lowest injection energies of 0.11 and 0.17 eV, along with the regeneration energies of 1.18 and 1.12 eV, respectively. The dyes reported here may have promising applications in photoanode for enhancing the performance of DSSC.

First principles methods are implemented in order to design new metal free organic dyes with motivation to improve photoinjection in dye sensitized solar cell (DSSC). The simulated structures obey general D‐π‐A structure and various structural modifications are made in π‐bridge as well as donor assembly of the dyes. The addition of benzothiadiazole and pyridine in π‐bridge caused shifting of absorption spectrum of dyes shifted toward lower energies. The analysis of structural and photoelectric properties of the dyes revealed that the dyes containing triarylamine in donor assembly show largest light harvesting efficiencies. The process of photoinjection was modeled by adsorbing the series of dyes on surface of (TiO2)n particles to investigate the injection and recombination kinetics. The dyes having benzothiadiazole in π‐bridge exhibited smallest injection energies while the dyes having pyridine in the in π‐bridge shown highest recombination energies. The detailed investigation of UV‐visible spectra of dye‐semiconductor complex was carried out to explore suitability of the dyes for practical applications in DSSC.

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