Effective electron acceptor materials usually have a deep lowest unoccupied molecular orbital (LUMO) energy level that can split excitons and generate current. A non-fullerene electron acceptor (F8-DPPTCN) was developed, using fluorene as the core with arms of diketopyrrolopyrrole (DPP) having thiophene-2-carbonitrile as the terminal units. The new molecule had a LUMO of -3.65 eV and a narrow bandgap (Eg) of 1.66 eV, owing to the electronegativity of the thiophene-2-carbonitrile group and its conjugation with DPP units. Organic solar cells (OSCs) with F8-DPPTCN as the acceptor and poly(3-hexylthiophene) (P3HT) as the donor were fabricated. A power conversion efficiency (PCE) of 2.37% was obtained with an open-circuit voltage (Voc) of 0.97 V, a short-circuit current (Jsc) of 6.25 mA cm-2, and a fill fator (FF) of 0.39. Structural characterization showed that P3HT and F8-DPPTCN were kinetically trapped in a weakly spearated state whereas thermal annealing led to a crystallization of P3HT and the formation of a network structure with a mesh-size of sevral hundred nanometers. When a solvent additive, diiodooctane, was used and the mixture were thermally annealed, both the P3HT and the F8-DPPTCN crystallized and a multi-length scale network was formed. Though the PCEs were low, the changes in the PCE could be correlated with the morphology changes, opening pathways to increase performance further.
        The paper was published on Journal of Materials Chemistry A.

huixing Li, Jielin Yan, Chang-Zhi Li, Feng Liu,* Minmin Shi,* Hongzheng Chen* and Thomas P. Russell, J. Mater. Chem. A, 2016, 4, 3777-3783.

链接：http://dx.doi.org/10.1039/c6ta00056h