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π-spacer engineering of metal-free PFCH dyes: a computational approach towards efficient indoor–outdoor DSSCs

Javeria Saeed, Riaz Hussain, Muhammad Durair Sajjad Haider, Aniqa Irshad, Maqbool Ahmad, Ajaz Hussain, Riaz Hussain, Khurshid Ayub, and Saleh S. Alarfaji

Department of Chemistry, Ghazi University, Dera Ghazi Khan, Pakistan

E-mail: jsaeed543@gmail.com

Abstract:

This study introduces a computational design of π-spacer modified PFCH (Phenazine-Furan-Carbazole-Heterocycle) dyes (PFCH-α–PFCH-ε), derived from a reference PFCH-Ref dye. This is a low-cost and scalable approach for next-generation Dye-Sensitized Solar cells (DSSCs). Using Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) (B3LYP/6-311G(d,p), the electronic, optical, and photovoltaic characteristics were comprehensively investigated. Structural analysis confirmed enhanced planarity in the modified dyes, as reflected by reduced Molecular Planarity Parameter (MPP) and Span Deviation from the Plane (SDP) values. Meanwhile, Reduced Density Gradient (RDG) and Non-Covalent Interaction (NCI) analyses highlighted the dominant stabilizing interactions. Frontier Molecular Orbital (FMO) results revealed narrowed band gaps (E_g), with PFCH-δ exhibiting the lowest E_g (1.99 eV), supporting efficient charge transport. UV–Vis spectra displayed notable bathochromic shifts, with PFCH-δ achieving the longest λ_max (694 nm), and attaining the strongest Light-Harvesting Efficiency (LHE) = 0.6. Charge migration pathways, confirmed through Transition Density Matrix (TDM), Charge Density Difference (CDD), and electron–hole overlap, established efficient donor–π–acceptor charge transfer in PFCH-δ and PFCH-β. Furthermore, reorganization energies (λ_e/h) and charge transfer integrals (t_e/h) identified PFCH-δ as the most effective carrier transporter. Photovoltaic parameters reinforced its superior performance, with the lowest binding energy (0.21 eV), highest open-circuit voltage (V_oc = 1.75 V), Fill Factor (FF = 0.92), and favorable short-circuit current density. Molecular Electrostatic Potential (MEP) mapping confirmed directional charge transfer, while adsorption studies demonstrated robust dye-TiO₂ interaction, validating strong surface anchoring. Collectively, π-spacer engineering of PFCH dyes enables multifunctionality (DSSC sensitizers and nonlinear optical materials), reduces energy losses via spontaneous ΔG_-inject and low-energy photon harvesting, and ensures spectral adaptability under both solar and artificial light. Hence, it enhances stability through improved hardness, charge transfer directionality, and dye lifetime.

Graphical abstract

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-025-04517-3

Chemical Papers 80 (3) 2307–2332 (2026)