Sensitizer-controlled charge transfer and optoelectronic properties of thiophene-cyanoacrylic-acid sulfonyl functionalized fragments anchored on TiO2 nanocluster for efficient organic solar cells

Abstract

Herein, a mechanistic molecular engineering strategy was set up to prepare a series of efficient Donor–bridge–Acceptor (D–π–A) sensitizers for dye-sensitized solar cells (DSSCs). The essential core of these dyes is the TCAS₁ reference, with substantial varying donors on the structural molecular chain. To analyze geometrical, optoelectronic and photovoltaic properties of the considered sensitizers (TCAS₁–₆), the DFT/TD-DFT approaches were used. The position of the π-Sulfonyl-bridge on the TCAS structure influenced the optoelectronic properties of DSSCs. The TCAS₁–₆ were adsorbed on the Nanocrystalline TiO₂ cluster surface. The evaluations of the optical charge transfer of TCAS₁–₆ along with different analyses including frontier molecular orbitals (FMOs) and molecular electrostatic potential (MEP) are explored. Indeed, the important parameters including, open-circuit voltage ($V_{oc}$), fill factor ($FF$), short-circuit current density ($J_{sc}$), light-harvesting efficiency ($LHE$), electron injection force ($\Delta G_{inj}$), dye regeneration force ($\Delta G_{reg}$), dye recombination energy ($\Delta G_{rec}$), reorganization energies ($\lambda$), density of states (DOS) and transition density matrix (TDM) maps are estimated to see the effect of π-Sulfonyl-bridge group. Moreover, all of the TCAS₁–₆ dyes showed significant UV–visible absorption and exhibited higher absorption (471–562 nm) compared to the reference TCAS₁ dye (478 nm). The designed TCAS₆ dye shows most enhanced optoelectronic characteristics, with higher band gap energy of 2.37 eV, higher dipole moment ($\mu =10.28Debyes$), higher maximum absorbance (562 nm), higher excited state lifetime $\tau =0.201ns$, and higher open-circuit voltage $V_{OC}=1.11V$ than the other dyes. Furthermore, the similarity of the adsorption energies was observed for all TCAS₁–₆ dyes, which reveal that the adsorption energy is not much, depend on the π-Sulfonyl-bridge insertion but rather on the anchored group. Therefore, the π-Sulfonyl-bridge insertion suggests that the change in π-bridge of dye photosensitizers can be a practical strategy to improve the charge transportation and efficiency in organic electronic materials.