Acceptor–donor–acceptor (A–D–A) structural molecules as donor materials in organic solar cells with improved efficiency: A DFT/TDDFT approach

The low power conversion efficiency of organic solar cells (OSCs) is a major concern in organic solar cell technology. In this work, we consider an acceptor–donor–acceptor configuration of a non-fullerene-based organic molecule; four donor small molecules are derived from the parent donor, DRTB-T. Calculations are performed using Gaussian 16 software at the density functional theory and time-dependent density functional theory levels with the basis set B3LYP/6-31G, with some of the open-circuit voltage (Voc) calculations repeated using an alternative basis set PBE0/def2-TZVP. The properties of the four derived donor molecules and acceptor molecules are examined. The new donor molecules contain 4CP, 4SCH, 4Br, and 4CN substituents and are combined with the IT4F derivative acceptor, which has dibenzotetrathiafulvalene side chains. Relevant quantum mechanical physico-chemical properties, such as the lowest unoccupied molecular orbital and highest occupied molecular orbital energy levels, Voc, reorganization energies, and fill factors, are computed. In addition, UV-VIS spectra analyses are performed to probe the solar radiation absorptivity of the molecules. The cells with 4CN recorded a 2.08 V Voc and a power conversion efficiency (PCE) of 32.89%, while the cells with 4SCH, having a Voc value of 1.92 V, recorded a PCE of 30.03%. These results show that substituting the peripheral thiophene molecules on the parent donor DRTB-T with 4CN, 4CP, 4SCH, and 4Br and combining the donors with the acceptor (IT4F derivatives) improves the open circuit voltage and power conversion efficiency of OSCs.