Photophysical properties of donor(D)-acceptor(A)-donor(D) diketopyrrolopyrrole (A) systems as donors for applications to organic electronic devices

Abstract

Fourteen substituted diketopyrrolopyrrole (DPP) molecules in a donor (D)-acceptor (DPP)-donor (D) arrangement were designed. We employed density functional theory (DFT), time-dependent DFT and the ab initio wave function second-order algebraic diagrammatic construction (ADC(2)) methods to investigate theoretically these systems. The aromatic substituents have one, two or three hetero- and non-hetero rings. We comprehensively investigated their optical, electronic and charge transport properties to evaluate potential applications in organic electronic devices. We found that the substituents based on one, two or three aromatic rings bonded to the DPP core functioning as a donor can improve the efficiency of an organic solar cell by fine-tuning the HOMO/LUMO levels to match acceptors in a bulk heterojunctions with PC61BM and the non-fullerene small-molecule ITIC (3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone)-5,5,11,11-tetrakis(4 hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]-dithiophene) acceptors. Several properties of interest for organic photovoltaic devices were computed. We show that the investigated molecules are promising for applications as donor materials when combined with typical acceptors in bulk heterojunctions because they have appreciable energy conversion efficiencies resulting from their low ionization potentials and high electronic affinities. This scenario allows a more effective charge separation and reduces the recombination rates. A comprehensive charge transfer analysis shows that the D – A (DDP) – D systems have significant intramolecular charge transfer, further confirming their promise as candidates for donor materials in solar cells. The significant photophysical properties of DPP derivatives, including the computed high quantum yields of fluorescence emission, also allow these materials to be used in organic light-emitting diodes (OLEDs).