New Molecular Donors with Dithienopyrrole as the Electron-Donating Group for Efficient Small-Molecule Organic Solar Cells

Six new molecules with donor–acceptor–acceptor (D–A–A) configuration bearing coplanar electron-donating dithieno[3,2- b:2′,3′- d ]pyrrole (DTP) or aryl-substituted DTP as the D unit and the electron-withdrawing pyrimidine–dicyanovinylene or benzothiadiazole–dicyanovinylene as the A–A block are synthesized. The introduction of aryl groups ( p -tolyl or p -anisolyl) onto the α position of DTP is found to greatly benefit the chemical stability and extend the molecular conjugation of the DTP-based D–A–A molecules. The observed broad absorption spectra and anisotropic molecular orientation in the thin films allow for these new D–A–A molecules to perform good capability of light harvesting. These new D–A–A donors are subject to the fabrication of vacuum-processed small-molecule organic solar cells (SMOSCs). The results showed that the structural modulation on the central A block (pyrimidine versus benzothiadiazole) as well as the terminal substitution ( p -tolyl versus p -anisolyl) give an evident trade-off between the open circuit voltage ( V oc ) and short circuit current density ( J sc ) values. Among them, SMOSC-adopted D–A–A molecule TDPM composed of a p -tolyl terminal group and a D–A–A configuration of DTP–pyrimidine–dicyanovinylene as the electron donor combined with C 70 as the electron acceptor shows a J sc of 11.34 mA/cm 2, a V oc of 0.94 V, and a fill factor (FF) of 0.52, giving a best power conversion efficiency (PCE) as high as 5.6%.