2D Lead Iodide Perovskite with Mercaptan-Containing Amine and Its Exceptional Water Stability

Two dimensional (2D) hybrid perovskites have attracted a great deal of interest because of their appropriate photovoltaic efficiency and environmental stability. Although some 2D hybrid perovskites with sulfur-containing amines have been reported, the cation having the mercaptan group has not been well explored yet. In this work, cysteamine (Cya, HS(CH₂)₂NH₂), a mercaptan-containing amine, was introduced into 2D hybrid perovskite. Two 2D lead iodides with different structures, (HCya)₂PbI₄ (1) and (HCya)₇Pb₄I₁₅ (2), were isolated as a red low-temperature phase and a yellow high-temperature phase, respectively. X-ray single-crystal structural analysis showed that the red phase 1 is a single layered corner-shared perovskite and that the yellow phase 2 is a corner/edge-shared quasi-2D perovskite. A thermo-induced reversible 1 to 2 phase transition was found in this synthetic system. The configuration of HCya cation greatly influences the crystallization equilibrium, generating different structures of the lead halides. The single-crystal structure of 1 is discussed in comparison with that of (HAE)₂PbI₄ (AE = HO(CH₂)₂NH₂), an analogue of 1. The different effects of OH and SH groups on the 2D frameworks are studied based on their hydrogen bonding properties. More remarkably, although the two perovskites have similar structures, the (HCya)₂PbI₄ (1) has an intrinsic water stability that is much more stable than (HAE)₂PbI₄, which should be attributed to the affinity of the SH group with lead on the surface of the lead halide.