Molecular engineering of benzodithiophene and diketopyrrolopyrrole-contained push-pull small molecules for efficient solution-processed organic solar cells

To investigate the relationships between molecular structures and their photovoltaic performance in solar cells, molecular engineering of push-pull small molecules from D-A to A-D-π-D-A architectures is proposed here using benzodithiophene, diketopyrrolopyrrole and fluorine-substituted phenyl groups as D, A and conjugated π units, respectively. In contrast to BDT-DPP, A-D-π-D-A structured DBDT-DPP-BF not only exhibits largely improved optical properties and matched energy levels, but also displays much ordered molecular packing and balanced hole/electron mobility in transistors. Therefore, compared with the inferior photovoltaic performance for BDT-DPP (PCE = 0.29%), the maximum PCE value of 5.27% with a significantly improved J _sc value of 12.01 mA/cm ² is finally achieved in DBDT-DPP-BF-based solar cells, indicating that manipulating molecular backbone from D-A to A-D-π-D-A architectures in the benzodithiophene and diketopyrrolopyrrole-contained push-pull small molecules here is an efficient method to enhance their photovoltaic performance in solar cells.