Diketopyrrolopyrrole based highly crystalline conjugated molecules for application in small molecule donor-polymer acceptor nonfullerene organic solar cells

In order to specifically investigate the low efficiency of small molecule donor-polymer acceptor (M-P) nonfullerene organic solar cells, we have successfully modify the synthesis of a series of D-pi-A-pi-D conjugated molecules containing diketopyrrolopyrrole (DPP) and different end groups. By incorporation of end group with different size of pi-conjugation (benzene, naphthalene and pyrene), we further improved the fill factor (FF) and short current density (J(sc)) of the donors molecule. Our experimental results and theoretical calculations have proven that the size of the end groups can influence the molecule crystallinity, mobility and intermolecular packing by altering the molecular coplanarity. As the result of improved crystallinity, morphology and fine-tuned mobilities, we demonstrated an increased FF, ahigh J(sc) of -4.5 mA/cm(2) and a power conversion efficiency of 2.05%, which is among the highest efficiency reported for M-P nonfullerene solar cells. Our results provide opportunities and possibilities of achieving higher performance M-P nonfullerene solar cells in the future. (C) 2016 Elsevier B.V. All rights reserved.