• Dahlström, Staffan
• Candeias, Nuno R.
• Salunke, Jagadish
• Vale, Joao R.
• Priimagi, Arri
• Guo, Xing
• Nyman, Mathias
• Vivo, Paola
• Österbacka, Ronald
• Chang, Jingjing

Abstract

Halide perovskite solar cells (PSCs) have recently received tremendous attention, due to their low-cost, high flexibility, low-temperature processing, and the skyrocketing rise of their power conversion efficiency (PCE), from 3.8% to 23.7%, in less than a decade.[1] HTMs play a key role in PSCs not only to facilitate the hole-transfer from perovskite to the electrode and to suppress recombination, but also to protect the perovskite surface against its degradation by moisture/oxygen.[2]<br/><br/>To date, most of the high performing PSCs are either based on small molecular 2,2’,7,7’-tetrakis(N,N-di-p-methoxyphenylamine)-9,9’-spirobifluorene (Spiro-OMeTAD) HTM, or on the polymeric poly-[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) HTM. However, these materials are tremendously pricey (320 $/g and 2190 $/g, respectively), being synthesized in modest yields by means of toxic palladium (Pd) catalyzed cross-coupling reactions that require stringent conditions and demanding purification, thus limiting their low-cost large-scale production.[2,3] Hence, designing simple, low-cost, and environmental friendly HTMs would be highly important towards the goal of eco-friendly PSCs.<br/> <br/>We report on two new phenothiazine-based HTMs functionalized with azomethine moieties, namely AZO-I and AZO-II. Both the materials are synthesized in excellent yields from cheap and green precursors, via a Pd-free synthetic route with only water as by-product. To the best of our knowledge, AZO-I and AZO-II are to date the first and the cheapest (~14 $/g) phenothiazine-based eco-friendly HTMs, with a significant gain in cost-effectiveness of nearly 22 times with respect to the commercially available Spiro-OMeTAD. When AZO-I and AZO-II were employed in PSCs, they led to PCE up to nearly 13% and 14%, respectively. Under similar conditions, devices based on the expensive and toxic Spiro-OMeTAD HTM exhibited PCE up to 18.7%. Hence, our results show that, in spite of a small loss in the overall PSC performance, AZO-I and AZO-II are competitive with respect to state-of-the-art HTMs, holding a great potential for future cost-effective, high performing, and eco-friendly HTMs with minimized environmental impact.<br/>

Topics

• perovskite
• surface
• Oxygen
• laser emission spectroscopy
• amine
• power conversion efficiency
• palladium