A Rational design of Dithieno-Benzo-Dithiophene based acceptors for organic solar cells

Abstract

Here, a series of Acceptor–Donor–Acceptor (A–D–A) type compounds are designed. We have theoretically investigated their structural, electronic, optical and photovoltaic properties by employing density functional theory (DFT) formalism. In this regard we have taken Dithieno[2,3−d;2/,3/−d/]benzo[1,2−b;4,5−b/]dithiophene (DTBDT) as donor unit and fused benzothiadiazole along with thiophene (spacer) and cyanoacrylic acid (CAA) (as anchoring group) as acceptor unit. We have investigated different structural and optoelectronic properties viz. dihedral angle, inter-ring bond length, bond length alternation parameters, HOMO-LUMO gap, ionization potential, electron affinity, partial density of states, reorganization energies for holes and electrons, charge transfer rate for holes and electrons, optical absorption and photovoltaic performances of all the designed molecules. Observed reorganization energy and charge transfer rate indicates the electron transporting nature of all the studied molecules. Calculated absorption properties reveal that compounds substituted with different heterocyclic rings in the donor part exhibits the higher value of absorption maximum in the visible range of electromagnetic spectrum. However, the lower values of exciton binding energy and negative Gibb’s free energy change of all the designed molecules indicate the facile charge separation at the donor/acceptor interface. Moreover, the observed photovoltaic properties indicate that all the studied compounds has potential to become candidate for application in photovoltaics. Observed theoretical power conversion efficiency (PCE) reveal that TTPy having maximum PCE of 18.44% will be the best candidate for photovoltaic applications.