New diketopyrrolopyrrole-based organic dyes for highly efficient dye-sensitized solar cells

Three diketopyrrolopyrrole (DPP) dyes ( ICD-3 , ICD-4 and ICD-5 ) with a D-π-A conjugation were designed and synthesized, where a symmetric phenyl-DPP-phenyl unit was used to connect a substituted diphenylamine and a thienyl acrylic acid, and two n -hexyl or 2-ethyl-hexyl chains were introduced on the periphery of the DPP macrocycle. The dyes were characterized by photophysical, electrochemical, and density functional theory calculations. Among the three dyes, the ICD-5 -based DSC afforded the best photovoltaic performance: a short circuit photocurrent density ( J sc ) of 16.34   mA/cm 2 , an open circuit voltage ( V oc ) of 753   mV, and a fill factor ( FF ) of 0.74, corresponding to an overall conversion efficiency ( η ) of 9.10% using I − / I 3 − redox couple-based liquid electrolyte under AM 1.5 conditions. The experimental results demonstrate that the DPP-based sensitizer is a promising option for DSCs, and rational molecular engineering is crucial for constructing highly efficient charge transfer sensitizers.