Hopping transport in triphenylamine and indoline based semiconductors in the context of dye sensitized solar cells: A DFT Study

Abstract

Dye-sensitized solar cells (DSSCs) have drawn a significant interest due to their low production cost, light weight, better flexibility in design, and better tunability. Herein, two metal free organic dyes based on donor-π-acceptor (D-π-A) type architecture having methoxy substituted triphenyl amine (TPA) and methyl substituted indoline(IND) as the donor units, cyanoacrylic acid (CA) as the acceptor unit, and 8H-thieno [2^', 3^':4,5]thieno[3,2-b]thieno[2,3-d]pyrrole (TTP) unit as π-bridge are successfully designed for fabrication of DSSCs. To tune the optical properties, structural engineering has been carried out at the TTP unit via substituting different +I groups, viz., -H, -CH₃, -OCH₃, -CH₂CH₂, -SH, and -OH and different -I groups viz. -CF₃, -COCH₃, -COOH and -CN. Various structural, electronic and optical parameters are calculated for the designed dyes. Our study reveals that dyes substituted with electron withdrawing groups possess lower Δ_H-L values for both TPA-CA and IND-CA groups of dyes. Moreover, the ESOP and GSOP values of all the dyes confirm the spontaneity of the electron injection and dye regeneration processes with respect to the conduction band of the TiO₂ surface and redox potential of the I^-/I₃^- redox couple. The absorption properties also manifest the red shift behavior of the designed dyes. Further, from the study of the structural and electronic properties of the dye-Ti₅O₁₀ clusters it is evident that the performance of the dyes get increased upon binding to the TiO₂ surface. Hence, our study provides a good recommendation for further designing of dyes to enhance the performance of DSSCs.

Keywords: Charge transfer rate; Density of states; Dihedral angle; Optoelectronic properties; Δ(H−L).