Cis/Trans Geometric Effect on the Electro-Optical Properties and Electron Injection in Indole-Based Squaraine Sensitizers: Quantum Chemical Investigations

Squaraine dyes gained significant attention as dye-sensitized solar cell (DSSCs) materials. In present study; we have studied the important parameters which influence the performance of DSSCs by considering the TiO2 clusters as acceptor material. We have investigated the structural, electro-optical and charge transport properties of six indole-based squaraine dyes (Cis-SQ1-SQ3 and Trans-SQ1-SQ3). The ground state geometries have been optimized by using density functional theory (DFT) then excitation energies and oscillator strengths were computed by time-dependent DFT in solvent. We shed light on the frontier molecular orbitals (highest occupied and lowest unoccupied molecular orbitals), electron injection (ΔGinject), relative electron injection (ΔG inject), electronic coupling constants (|VRP|), light harvesting efficiencies (LHE), short-circuit current density (Jsc) and open-circuit voltage (Voc). The ΔGinject, ΔG inject and |VRP| of six sensitizers have been compared with some previously studied sensitizers. The effect of donor (-OCH3) and acceptor (-COOH) groups has been investigated and discussed on said properties of interests. The Cis/Trans geometric effect has been studied on the structural parameters, absorption wavelengths, ΔGinject, |VRP|, LHE, Voc and factors affecting the Jsc. It has been discussed that which geometric isomer would be more favorable to enhance the performance of DSSCs.