DFT molecular modeling studies of D-π-A-π-D type cyclopentadithiophene-diketopyrrolopyrrole based small molecules donor materials for organic photovoltaic cells

Abstract A novel six D-π-A-π-D type compounds containing small molecules from cyclopentadithiophene (CPDT) and diketopyrrolopyrrole building (DPP) units were designed, as donors, for improving the efficiency of bulk hetero-junction solar cells. The geometries of the title compounds were optimized using the density functional theory at the hybrid functional B3LYP in combination with the 6−311 g(d,p) basis set. Electronic structures, photo-physical, optical and intra-molecular charge transfer properties have been investigated. The contour plots of the transition density matrix have been simulated for all compounds and used to evaluate the hole-electron localization, the donor-acceptor interaction as well as the electronic excitation processes in their excited states. The new designed donors have shown a large absorption in the visible range with interesting hole transport properties, resulted from their rigid-planar structures. The open circuit voltage and the fill factor were estimated. The present computational study showed that tuning the building blocks of the organic materials dispose a potential approach for further enhance the performance of small molecules donor materials in bulk hetero-junction (BHJ) organic solar cells.