Influence of end groups (4F, 4Br, 4CF3, and 4CBr3)of non-fullerene acceptor molecules on the performance of organic solar cells

The past decades have seen significant progress in organic solar cells based on asymmetric non-fullerene acceptors with power conversion efficiency (PCE) increasing from ≈1 to ≈19%. The Gaussian 09W was utilized to modify a reference acceptor molecule by end groups such as four fluorides, bromides, carbon trifluorides, and carbon tribromides. The DFT and TD-DFT methods were employed to calculate the optical and electronic characteristics of modified acceptor compounds and compare them to the reference compound. The key properties such as frontier molecular orbitals analysis, energy gap, electron affinity (EA), ionization potential (IP), chemical softness (S), chemical hardness (η), chemical potential (µ), electronegativity (χ), fill factor (FF), open circuit voltage (Voc), exciton binding energy, absorption maxima, and light harvesting efficiency (LHE) for acceptor molecules are calculated. The substitution of end groups in the acceptor molecules leads to a decrease in the energy gap from (R = 2.056 eV) to (R-4CBr₃ = 1.969 eV) and an increase in maximum absorption wavelength from (R = 664.416 nm) to (R-4CBr₃ = 699.083 nm). The behavior of our results is consistent with the experimental results, which helps to increase the efficiency of non-fullerene acceptors-based organic solar cells.