Novel W-Shaped Oxygen Heterocycle-Fused Fluorene-Based Non-Fullerene Acceptors: First Theoretical Framework for Designing Environment-Friendly Organic Solar Cells

Abstract

The increasing demand of energy has expedited the research on developing low-cost and environment-friendly organic solar cells (EFOSCs). The commercial application of non-fullerene-fused ring electron acceptors (FREAs) having the 1,1-dicyanomethylene-3-indanone (IC) end group is limited due to the presence of two highly toxic −C≡N groups. This research projects the first theoretical design and exploration of environment-friendly groups transforming promising end-capped electron acceptor molecules for high-performance environment-friendly organic solar cells. For the first time, we developed FCO-based (acceptor–donor–acceptor (A–D–A)) type, novel W-shaped environment-friendly electron acceptor molecules (W1–W6) by modifying the toxic −C≡N group of FCO (reference synthesized molecule R) with three nontoxic electron-withdrawing (−CF3, −SO3H, −NO2) groups. Frontier molecular orbital (FMO) analysis, density of state (DOS) graphs, electron and hole reorganization energy (λe, λh), open-circuit voltage (Voc), transition energy, transition density matrix (TDM) analysis, and exciton-binding energy values of W1–W6 are computed and compared with those of the recently synthesized highly efficient FCO molecule. Results suggest that the photovoltaic, photophysical, and electronic properties of designed molecules W1–W6 are better than those of R. All developed molecules, especially W6, proved to be the preferable optoelectronic material for EFOSCs owing to their low-energy band gap (2.136 eV), highest λmax values of 709.25 and 792.08 nm in gas and chloroform, respectively, with lowest transition energy (1.75 eV), lowest electron mobility (λe = 0.007657 Eh) and hole mobility (λh = 0.006385 Eh), lowest binding energy (Eb = 0.072 eV), and 1.743 V value for open-circuit voltage (Voc) as compared to reference R as well as other developed molecules. Charge transfer analysis among the W6:PM6 blend proved the superposition of orbitals and successful transfer of charge from the highest occupied molecular orbital (HOMO) (PM6) to the lowest unoccupied molecular orbital (LUMO) (W6). Thus, the developed molecules (W1–W6) depicting outstanding optoelectronic properties are recommended as the best nontoxic alternative materials for developing efficient and environment-friendly organic solar cells.