The effectiveness of new a electron acceptor for organic solar cells is demonstrated. The acceptor is a homoleptic zinc(II) complex of 2,6-diphenylethynyl-1,3,7,9-tetraphenylazadipyrromethene. The high power-conversion efficiency obtained is attributed to the acceptor's 3D structure, which prevents crystallization and promotes a favourable nanoscale morphology, its high Voc , and its ability to contribute to light harvesting at 600-800 nm.

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Small internal reorganization energy is desirable for high-performance optoelectronic materials, as it facilitates both charge separation and charge transport. However, only a handful of n-type electron accepting materials are known to have small reorganization energies. Here, DFT calculations were performed to predict the reorganization energy of azadipyrromethene-based dyes and their complexes. All compounds studied were most stable in their anionic state and had high electron affinity, indicating their potential as n-type material. The homoleptic zinc(II) complexes had significantly lower reorganization energies than either the free ligands or the BF2(+) chelates. The low reorganization energies of the zinc(II) complexes are explained by the large and rigid π conjugated system that extends across the two azadipyrromethene ligands via interligand π-π interactions. This work suggests that Zn(II) complexation is a novel strategy for obtaining materials that combine low internal reorganization energy with high electron affinity for the development of novel n-type optoelectronic materials.

Solution-processable conjugated oligomers incorporating red-light absorbing azadipyrromethenes (aza-DIPY) within the main chain were synthesized via palladium-catalyzed Sonogashira coupling reactions. Thin films of these compounds absorbed light up to ∼1000 nm and displayed reversible reductions as ascertained by cyclic voltammetry experiments. Reactions with trifluoroboron etherate yielded materials displaying a unique combination of good solubility in organic solvents, low optical band gaps (∼1.3 eV), and high electron affinity (∼4.5 eV).

A structure–property study of non-fullerene acceptors based on azadipyrromethene derivatives was performed. Power conversion efficiencies between 2 and 4% were obtained when blended with poly(3-hexylthiophene) as the donor.