Haibo, in collaboration with colleagues from The Chinese University of Hong Kong has proven that large cations like Guanidium can fit into the perovsikte lattice with simultaneous introduction of the small-size ions like Cs+ and Br.

In this research, FAPbI3 was used as a basic framework and Cs+ and Br as substitutional ions to investigate the role of lattice composition in GA+ incorporation. The key finding is that simultaneous introduction of the small-size Cs+ and Br ions in the FAPbI3 lattice is critical for creating sufficient space to accommodate the large GA ions and that the presence of the Cs+ ions prevents the formation of a GA-contained low-dimensional phase, which both assist GA+ incorporation in the three-dimensional FAPbI3 perovskite lattice. Once entered the perovskite lattice, the GA+ ions can stabilize the lattice structure via forming strong hydrogen bonds with their neighboring halide ions. Such structure modification suppresses halide vacancy-formation, thus leading to improved material properties and also solar cell performance. The combined theoretical and experimental work has been published on Advanced Functional Materials.

Reference: Y. Zhou, H. Xue, Y. H. Jia, G. Brocks, S. Tao and Ni Zhao, Enhanced incorporation of Guanidium in Formamidinium-based perovskites for efficient and stable photovoltaics: the role of Cs and Br, Advanced Functional Materials, 2019, 1905739.