DFT modeling of new (2,2'-(1,4-phenylene)bis(quinazolin-4(3H)-imine) (PBQI) based copolymers for photovoltaic applications

Abstract

In this work, we designed two novel donor-acceptor (D-A) copolymers based on 2,2'-(1,4-phenylene)bis (quinazolin-4(3H)imine) (PBQI) as potential donor materials for organic photovoltaic (OPV) devices. We studied the properties of these copolymers using density functional theory (DFT) and time-dependent DFT (TD-DFT) at the 6–31g (d) theory level. We first examined and compared the optoelectronic properties of the thiophene-alt-PBQI (TH-PBQI) and N-vinylcarbazole-alt-PBQI (VK-PBQI) copolymers. Then, we studied the copolymer resulting from connecting the successive units of 3-thiophene via a carbon bridge, namely the polycyclopentadithiophene-alt-(2,2'-(1,4-phenylene)bis (quinazolin-4(3H)-imine)) (CPDT-PBQI). Finally, in an attempt to improve the optoelectronic properties of CPDT-PBQI, two vinylene groups were inserted as π-conjugated spacers in the main chain of CPDT-PBQI to obtain CPDT-π-PBQI. Interestingly, compared to CPDT-PBQI, CPDT-π-PBQI showed more planar conformation, lower band gap, more spatially delocalized HOMO and LUMO states, and red-shifted absorption. Consequently, we propose CPDT-π-PBQI copolymer as an electron donor for building heterojunction with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as the electron acceptor.