Theoretical designing of symmetrical non-fullerene acceptor molecules by end-capped modification for promising photovoltaic properties of organic solar cells

Non-fullerene small molecules must absorb in a broader wavelength range for achieving high efficiencies. This work presents seven indacenodithiophene core-based acceptor molecules (SJA1-SJA7) designed by structurally tailoring the pre-existed SJ-IC molecule. Detailed studies of these newly designed molecules were carried out to analyze the stabilization of energy levels, planarity, UV–Visible absorption, light-harvesting efficiency, open circuit voltage (Voc), and other photovoltaic properties. Structural modification with different acceptors resulted in the narrowing of band gap and broader absorption spectrum. All the newly reported molecules showed significant redshift having λmax values ranging from 686 nm to 722 nm in the gas phase and 742 nm to 792 nm in chloroform as compared to SJ-IC which has λmax values at 675 nm and 732 nm in gas and chloroform medium respectively. Moreover, newly presented molecules exhibited lower excitation energy values and higher oscillator strength than SJ-IC molecule which indicate effective charge transfer between frontier molecular orbitals. Improved charge mobilities were observed as newly developed molecules possessed lower internal reorganization energies. These findings were further confirmed by molecular electrostatic potential (MEP) and transition density matrix (TDM) analysis. In case of Voc, SJA7 emerged as a more proficient molecule due to its higher value (1.440 eV) than SJ-IC (1.42 eV). These results assure the remarkable improvement in optoelectronic properties of designed molecules which makes them a better choice than pre-existing SJ-IC molecule for the development of improved OSCs in the future.