Phenyl-9H-Phenothiazine and phenyl-9H-Phenoxazine-based metal free dye-sensitizers (D-A2-π-A1) with thieno[3,4-b]pyrazine auxiliary acceptor for Dye-Sensitized Solar Cell applications: DFT and TD-DFT computational studies

Abstract

This work presents computational investigation on the structural, optoelectronic properties and performance characteristics of phenyl-10H-phenothiazine (PPTZ)/phenyl-10H-phenoxazine (PPOZ)-based D-A2-π-A1 dye-sensitizers using DFT/TD-DFT method at B3LYP/6-31G** level. The designed dyes are found to have large charge separations, supported by the frontier orbitals and electrostatic maps, which demonstrate that the donor and acceptor units can engage in intramolecular charge transfer in form of push–pull of electron from donor to acceptor unit. The LHE values are arranged as: PPTZ4 (0.9702) > PPTZ2 (0.9574) > PPOZ3 (0.9562) > PPOZ2 (0.9380) > PPTZ1 (0.9302) > PPOZ4 (0.9291) > PPOZ1 (0.8892) > PPTZ4 (0.7916) > PPTZ5 (0.7861) > PPOZ5 (0.7696). The open circuit (V_OC), injection and regeneration drive forces (ΔG_inject and G_regen), rate of electron transport process (k), total reorganization energy ( $ {\lambda _{total}} $ ${\lambda }_{\mathrm{total}}$) favor PPTZ dyes, which increases $ {J_{SC}} $ $J_{\mathrm{SC}}$ and ultimately lead to high photoexcitation and better performance as dye-sensitizers. The dipole moment, polarizability and hyperpolarizability also show that PPTZ dyes should have higher ICT and electron injection abilities than PPOZ dyes. However, most of the calculated optoelectronic properties favor PPTZ4 and PPTZ5 dyes, although the energy band gap, reorganization energy, injection drive force, coupling constant and rate of electron transfer show that PPOZ5 dyes has outstanding characteristics among PPOZ dyes.