Heteroatom-bridged benzothiazolyls for organic solar cells: a theoretical study

On the basis of a typical organic photovoltaic (OPV) building block of 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (DTBT), a series of novel DTBT derivatives were designed following a heteroatom-bridging strategy to take advantage of the diversified interactions between heteroatoms and π-conjugated systems. These heteroatom-bridged DTBTs, whose outer electron-rich thiophene moieties are covalently fastened to the central electron-deficient benzothiadiazole with additional heteroatom bridges, exhibit promising features for OPV applications with rigid molecular structures, properly lain frontier molecular orbitals (FMOs), broad and intense absorption spectra, and adequate charge transport properties, as revealed by systematic theoretical calculations on molecular geometries, FMOs, absorption spectra, and relaxation and reorganization energies. The structure-property relationship investigations show that the mono-/di-heteroatom bridging is effective not only in tuning the rigidity of the molecular geometries but also in adjusting the optoelectronic properties of the resulting materials. Among the studied heteroatoms, the C and Si were found to be the most efficient in designing novel molecules for OPV applications. These theoretical insights may provide a solid basis for experimental synthesis and device investigations of the proposed heteroatom-bridged DTBTs as potential high-performance building blocks for bulk heterojunction OPV molecules.