Tuning the optoelectronic properties of dibenzochrysene (DBC) based small molecules for organic solar cells

Abstract

Four different types of dibenzo chrysene (DBC) based molecules (A1-A4) are designed to investigate their photovoltaic properties via quantum simulation. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) analysis is performed to explore various parameter of solar cells i.e. the 3-D geometries of designed molecules, photovoltaic properties, reorganization energies, dipole moment, transition density matrix (TDMs), open-circuit voltage (Voc) and Exciton Binding Energy (Eb). We have performed a comparative study between designed molecules and reference structure to R to conclude our results. Among all designed structures, A4 has shown a red shift with λ max of 797.4 nm and band-gap (ΔH-L) of 1.743eV in CHCl3 by B3LYP/6-31G (d,p) using the IEFPCM model. The internal reorganization energy of all the designed molecules has shown a more effective charge transfer property as compared to R. However, A4 has shown the least value of λe (0.003775 a.u), thus have good charge transferability in the form of electron This high charge transfer ability ascribed to strong electron-withdrawing malononitrile group that enhances the rate of charge transmission among donor and acceptor groups. Transition density matrix (TDM) map results have shown that A2 has weak electrostatic interaction between electron and hole (Eb = 0.1126 eV) showing ease dissociation of exciton in comparison to other molecules. This DFT based quantum simulation explicates that we can amend different properties of solar cells by attachment of different end capped acceptor units around the central donor core. Thus high device performance (PCE) could be achieved by appropriate choice of donor and acceptor units.