Guidelines for Designing Water-Stable Hybrid Lead Bromide Perovskites with Broad Emission

Hybrid lead halide perovskites have generated increasing attention for their high performance in optoelectronic applications. One main drawback of these materials is the sensitivity to moisture, which contributes heavily to the ultimate decomposition. Here, this study takes advantage of the reported representative white-light emitting lead bromide perovskite and three-dimensional (3D) perovskite as the subject of water-stability study. It is reported here that other than observed phase transformation in one case, the majority of these perovskites break down in water rapidly, precipitating out as an inorganic salt compound Pb3Br6[H2O]center dot H2O. As these materials are studied in detail, it is discovered that better coverage of the hydrophobic organic cation enhances the water stability. Taking this idea further, it is demonstrated here that five new one-dimensional (1D) lead bromide compounds have superior water stability, where the longest stability when completely immersed in water is more than one year and counting. This work provides a new mechanism regarding the degradation process when encountering moisture and general guidelines to increase the water stability for the lead bromide hybrids. The degradation pathway and product in water of a series of representative lead bromide perovskites is revealed. Learning from this process where high organic cation coverage is required for better water stability, a series of lead bromide hexagonal perovskites with high water stability have been further demonstrated.image