Phenanthrene-functionalized 3,6-dithiophen-2-yl-2,5- dihydropyrrolo[3,4c] pyrrole-1,4-diones as donor molecules for solution-processed organic photovoltaic cells

3,6-Dithiophen-2-yl-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (DPP) based organic molecules and polymers have received strong attention as the donor materials of efficient organic photovoltaic cells (OPVs). This paper reports the synthesis and characterization of two DPP-based organic molecules functionalized with phenanthrene and ethynylphenanthrene and their application as the donor materials of solution-processed OPVs. They have band gaps of 1.61.8 eV and appropriate energy levels, and they can be soluble in common organic solvents such as chloroform and tetrahydrofuran. The C≡C triple bond in ethynylphenanthrene has a strong effect on the structure and properties of molecules. It increases the rigidity of molecule, decreases the solubility in organic solvents, and increases the crystallinity of the active layer and photovoltaic performance of the OPVs. The optimal photovoltaic efficiency of OPVs with ethynylphenanthrene-functionalized DPP is 1.71% under AM 1.5 G illumination (100 mW cm^-2), more than double of that of the OPVs with phenanthrene-functionalized DPP.