The intrinsic moisture sensitivity of the hybrid perovskite ~ 5.---::--:---:----:--------..., methylammonium lead iodide (MAPI) calls for new synthetic strategies to ~ J..-1--~ J.-)"-enhance moisture resistance and, thus, long term stability. Here, we combine ;. 4 two strategies: (i) transitioning from 3D to 2D hybrid perovskites by inserting . § ~ larger A site cations as spacers and (ii) using fluorinated linkers to enhance the -3 3 hydrophobicity of the material-and identify two new hybrid perovskite type E ,II chloride and organic sublattices, respectively, both having clearly observable fingerprints in the solid state NMR spectra. DFT calculations trace the origin of the observed severe distortion of the inorganic sublattice in (F~H 4 NH 3 ) 2 PbCI 4 back to structural features including the formation of hydrogen bonds. The optical properties of (F~J-4NH 3 ) 2 PbCl 4 were characterized by optical absorption spectroscopy and time resolved photoluminescence measurements with a view toward the interaction between the organic and inorganic soblattices. The broad photoluminescence spectrum as well as specific absorption characteristics are assigned to exciton self trapping due to a strong coupling of the excited states to lattice distortions.• INTRODUCTIONResearch in the field of hybrid perovskites has experienced a rapid revival since the discovery of the superior optical and electronic properties of methylammonium lead iodide (MAPI) as an absorber material in solar cells. Its large absorption coefficient/ medium band gap/ and long hole and electron diffusion lengths, 3 combined with its solution processability, accelerated the development into one of the most important semiconductor materials for solid state solar cells.4 On the way to commercialization of hybrid perovskite solar cells, some challenges still have to be addressed, including the toxicity of lead and the poor moisture stability of MAPI type hybrid perovskites.

Hybrid perovskites have evolved into an exciting materials platform supporting a wide variety of optoelectronic applications including solar cells and light-emitting devices. In spite of their rapid deployment in devices, a detailed understanding of their structure−property relationships is scarce. In this study, we comprehensively analyze the crystal and electronic structures as well as thermal, optical, and electronic properties of a series of 2-(aminomethylpyridinium) lead halides including the isotypic hybrid perovskites (C 6 H 10 N 2 )PbX 4 (X = Cl, Br, and I) and the hybrid compound (C 6 H 10 N 2 ) 6 IPb 5 I 21 •3H 2 O. The thermal transformation of (C 6 H 10 N 2 ) 6 IPb 5 I 21 •3H 2 O into (C 6 H 10 N 2 )PbI 4 was studied by thermal analysis and powder X-ray diffraction and used to reverse engineer a synthesis route for phase-pure (C 6 H 10 N 2 )-PbI 4 . The very broad PL emission of (C 6 H 10 N 2 ) 6 IPb 5 I 21 •3H 2 O is traced back to the largest octahedral distortion found in this compound among all studied 2-(aminomethylpyridinium) lead halides. We further find that (C 6 H 10 N 2 )PbI 4 and (C 6 H 10 N 2 ) 6 IPb 5 I 21 •3H 2 O are mixed ionic−electronic conductors and identify the diffusing ionic species as iodine and protons, respectively, by combining solid-state NMR measurements with a.c. impedance spectroscopy and d.c. galvanostatic polarization measurements.