Molecular Screening of Different π-Linker-Based Organic Dyes for Optoelectronic Applications: Quantum Chemical Study

In this work, metal-free organic dyes (SZ-1–SZ-5) based on phenothiazine (PTZ) as donor (D) unit and different π-conjugated (π) as spacers and acceptors (A) representing cyanoacetic acid (D-π-A) have been investigated to examine their optoelectronic properties by density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. A favourable electron transfer into the semiconducting material (TiO₂) is effectively obtained by the optimized ground state HOMO-LUMO energy values of the SZ-3 molecule. The photovoltaic (PV) parameters of the oxidation and reduction potential energies (\(E^{dye}\) and \(E^{{dye^{*} }}\)), a driving force of electron injection (\(\Delta G_{inject}\)), dye regeneration (\(\Delta G_{reg}\)), light-harvesting efficiency (LHE), dipole moment (\(\mu_{normal}\)), short-circuit current density (\(J_{SC}\)) and open-circuit photovoltage (\(eV_{OC}\)) were obtained and are discussed in detail. On the other hand, the TD-DFT approach was used to calculate and describe the optical properties of all SZ-1–SZ-5 molecules in terms of absorption energy associated with maximum wavelengths (\(\lambda_{\max }\)), emission spectra (\(\lambda_{emi}\)), oscillator strengths (f) and excitation energies (E). Finally, the theoretical findings represent the various π-spacers in the optoelectronic capabilities of the D-π-A-based dye derivative materials, and they offer useful guidelines for future structures designed for solar cell applications.