In silico end-capped engineering of 4,4′-dimethyl-[2, 2′-bithiazole] core-based acceptor materials for high-performance organic solar cells

Abstract

Organic solar cells (OSCs) have grabbed the attention of researchers due to good power conversion efficiency, low cost, and ability to compensate for light deficit. The aim of the present research work is to increase the efficiency of previously synthesized reference (R) molecule 2,2′-((2Z,2′Z)-(((4,4′-dimethyl-[2,2′-bithiazole]-5,5′-diyl)bis(4-(2-butyloctyl)thiophene-5,2-diyl))bis (methaneylylidene))bis(5,6-dichloro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile by improving its photovoltaic properties via end cap engineering. Five new acceptors, namely, E1, E2, E3, E4, and E5, are used to substitute the end group of reference molecule. Several parameters have been analyzed using density functional theory including the absorption maxima, charge transfer analysis, frontier molecular orbital (FMO), open circuit voltage (V_oc), density of states (DOS), photochemical characteristics, transition density matrix (TDM), and the electron-hole reorganization energies to evaluate the efficiency of specially engineered molecules. All the engineered molecules (D1-D5) had smaller energy gap (4.50–4.71 eV) compared with reference (4.75 eV) and absorption maxima in the range of 443.37–482.67 nm in solvent phase due to end-cap acceptor modification. Fabricated molecules (D1-D5) showed smaller electron reorganizational energy values (0.18–0.27 eV) and V_oc ranging from 1.94 to 2.40 eV. Designed molecule D3 being an acceptor when blended with donor polymer (PTB7-Th) portrayed highest charge transfer capability owing to its smallest energy gap (4.50 eV) among all the engineered molecules. D5 molecule exhibits higher V_oc (2.40 eV), greater LHE (0.9988), and superior result of fill factor (94.15%) as compared with R, which leads to improve the efficiency of OSCs. Theoretical findings illustrated the superior behavior of all the designed molecules making them suitable aspirants to construct efficient OSC devices.