Solution Processable Small Molecules for Application to Organic Solar Cells

A novel series of diketopyrrolopyrrole (DPP)-based materials, 4-[{3-(thiophene-2-yl)-6-[5 ''-n-hexyl-(2,2'; 5',2 ''-terthiophene)-5-yl]-2,5-bis(2-ethylhexyl)pyrrolo[3,4-c]pyrrole-1,4(2H, 5H)-dione-5-yl}-N,N-diphenylbenzenamine] (TPA(DPP)), bis[{3-(thiophene-2-yl)-6-[5 ''-n-hexyl-(2,2'; 5',2 ''-terthiophene)-5-yl]2,5-bis(2-ethylhexyl) pyrrolo[3,4-c]pyrrole-1,4(2H, 5H)-dione-5-yl}-p-phenylene]-benzenamine (TPA(DPP) 2' and tris[{3-(thiophene-2-yl)-6-[5 ''-n-hexyl-(2,2'; 5',2 ''-terthiophene)-5-yl]-2,5-bis(2-ethylhexyl)pyrrolo[3,4-c] pyrrole-1,4(2H, 5H)-dione-5-yl}-p-phenylene]amine (TPA(DPP)(3)) has been designed and synthesized for use as donor materials in solution-processable organic solar cells. We describe the effect of modifying the molecular structure of the diketopyrrolopyrrole derivatives on the electronic and optoelectronic properties and the photovoltaic properties of the materials for OPV applications. Under optimized conditions, the DPP-based oligomers show power conversion efficiencies (PCEs) for the OPVs in the range 0.68-1.50% under AM 1.5 illumination (100 mW/cm(2)). Among the three oligomers, the star shaped TPA(DPP)(3) shows a power conversion efficiency of 1.50% with a short circuit current of 5.44 mA/cm(2), a fill factor of 0.44, and an open circuit voltage of 0.63 V.