Affordable Hole Transport Materials
In order to reduce the cost of hole transporting materials (HTMs) for perovskite solar cells we have prepared triphenylamine-based small molecules using simple amide-bond formation chemistry. Despite the lack of conjugation, our new HTM (EDOT-Amide-TPA) outperforms state-of-ther art materials in performance, showing over 20% power conversion efficiency and stability. The latter is attributed to the amide-bond, which is known to bind Lithium salts and prevent Li diffusion.
State-of-the-art perovskite-based solar cells employ expensive, organic hole transporting materials (HTMs) such as Spiro-OMeTAD that, in turn, limits the commercialization of this promising technology. Herein an HTM (EDOT-Amide-TPA) is reported in which a functional amide-based backbone is introduced, which allows this material to be synthesized in a simple condensation reaction with an estimated cost of <$5 g−1. When employed in perovskite solar cells, EDOT-Amide-TPA demonstrates stabilized power conversion efﬁciencies up to 20.0% and reproducibly outperforms Spiro-OMeTAD in direct comparisons. Time resolved microwave conductivity measurements indicate that the observed improvement originates from a faster hole injection rate from the perovskite to EDOT-Amide-TPA. Additionally, the devices exhibit an improved lifetime, which is assigned to the coordination of the amide bond to the Li-additive, offering a novel strategy to hamper the migration of additives. It is shown that, despite the lack of a conjugated backbone, the amide-based HTM can outperform state-of-the-art HTMs at a fraction of the cost, thereby providing a novel set of design strategies to develop new, low-cost HTMs.
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