Environment-friendly metal halide Tin (Sn) perovskite solar cells (PSCs) have attracted much attention and been considered as an ideal alternative of nocuous traditional Lead (Pb) counterparts due to its broader light harvesting range, lower binding energy, and higher carrier mobility. However, the power conversion efficiency (PCE) of Sn PSCs are well below that of their Pb counterparts (25.5% certified). In addition to lower efficiency, the poor stability is another problem in Sn PSCs. Recently, two-dimensional Ruddlesden-Popper (2DRP) Sn perovskites, with multiple quantum wells, have been widely reported to be more stable than 3D Sn perovskite owing to the introduction of hydrophobic bulky spacers and suppressed ion migration/self-doping effect. Taking both lower toxicity and improved stability into consideration, the 2DRP Sn PSCs provide a new way for approaching real industrialization of PSCs.
In 2DRP Sn perovskites, the competition between bulky spacers and ammonium salts (e.g. FA+), in which the bulky spacers prefer to limit crystal grow parallel to the substrate whereas the other ammonium salts tend to expand crystal grow vertical to the substrate, make the crystallization process become more complex and uncontrollable. Therefore, the bulky spacers play an important role in managing the crystallization process due to their unique degree of freedom in 2DRP Sn perovskites. However, the halide ions in traditional bulky spacers have less interaction with perovskite precursors, losing enough ability to control such complex crystallization process, which limit the development of 2DRP Sn PSCs.
In recent, Prof. Yonghua Chen and colleagues in Nanjing Tech University for the first time utilize new ionic liquid bulky spacer, butylammonium acetate (BAAcO), to replace traditional halide spacer, BAI, in 2DRP Sn perovskite to enhance the inter-component interaction and control the crystallization process. The AcO- functional group in BAAcO has a strong interaction with formamidine ions (FA+) and Sn2+ in precursor solution, leading to the formation of intermediates and the delayed crystallization rate. The strengthened interaction enables the high quality 2DRP Sn perovskite with narrow phase distribution and highly vertical crystal orientation. Benefiting from this high quality 2DRP Sn perovskite fabricated from BAAcO, the carrier extraction and transport are more efficient, favoring the PCE of solar cells up to 10.36% (7.16% BAI), which is the highest report in the state-of-the-art 2DRP Sn PSCs. Most importantly, the corresponding devices hold ~90% of initial efficiency after storage in N2 atmosphere for ~600 h without any encapsulation. This work shines new directions toward the exploration of novel bulky spacers for inter-component interaction enhancement and crystallization process control in 2DRP Sn perovskites.
See the article: Qiu J, Lin Y, Ran X, Wei Q, Gao X, Xia Y, Müller-buschbaum P, Chen Y. Efficient and stable Ruddlesden-Popper layered tin-based perovskite solar cells enabled by ionic liquid bulky spacers. Sci. China Chem., 2021, 64, https://doi.org/10.1007/s11426-021-1075-7
Science China Chemistry