Hybrid halide perovskite semiconductors have proven to be prominent candidates for many optoelectronics applications, spanning from solar cells and LEDs to photodetection and lasing. [1-2] They exhibit a unique combination of fine-tunable traits that cannot be met by any other class of semiconductors, deriving directly from their hybrid nature. Finding a way to generate porosity in this class of materials would allow them to be utilized in currently unexplored applications such as sensing, photonic crystals, integrated waveguides, and solid-state batteries. 

We recently developed a general strategy for generating porosity to hybrid metal halide materials using molecular cages serving as structure-directing agents and counter-cations. [3] The reaction of the [2.2.2] cryptand (DHS) linker with Pb(II) in acidic media gave rise to the first porous 2D metal halide semiconductor with formula (DHS)₂Pb₅Br₁₄. The corresponding material is stable in water for over a year, while gas and vapor sorption studies revealed that it can selectively and reversibly adsorb H₂O and D₂O at room temperature (RT). Solid-state NMR measurements and DFT calculations verified the incorporation of H₂O and D₂O in the organic linker cavities, and shed light on their molecular configuration. In addition to porosity, the material exhibits broad light emission centered at 617 nm with a full width at half-maximum (FWHM) of 284 nm (0.96 eV). The recorded water stability is unparalleled for hybrid metal halide and perovskite materials, while the generation of porosity opens up new pathways toward unexplored applications (e.g. solid-state batteries) for this class of hybrid semiconductors. This work sets the foundation for a new family of versatile hybrid semiconductors, namely porous metal halide semiconductors (PMHS), solving current stability material deficiencies, whereby means of molecular and crystal engineering, the path towards commercialization is open.