Toward Fluorinated Spacers for MAPI-Derived Hybrid Perovskites: Synthesis, Characterization, and Phase Transitions of (FC₂H₄NH₃)₂PbCl₄

Abstract

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.

Benzimidazolium Lead Halide Perovskites: Effects of Anion Substitution and Dimensionality on the Bandgap

“…[8] The transient, photo-induced formation of these self-trapped excitons has been observed to occur on a femtosecond (fs) -timescale and its multicomponent nature has been confirmed by temperature dependent and time-resolved PL measurements. [24][25][26] Note that all compounds studied here show similar levels of distortions of the inorganic sublattice, which is why the observed differences in the PL emission may result from different degrees of lattice "softness" or permanent lattice defects rather than (static) structural distortions.…”

Fluorinated Low‐Dimensional Ruddlesden–Popper Perovskite Solar Cells with over 17% Power Conversion Efficiency and Improved Stability

“…In early days, Mitzi et al adopted fluorinated 2D perovskite to fabricate thin‐film transistors and found that fluorine substitution on the organic cation of perovskite modifies the crystal structure, resulting in different transport properties . The theoretical calculation also predicted that a fluorine‐substituted organic spacer may distort the crystal structure of perovskite . Very recently, during our paper submission process, several latest publications also experimentally demonstrate that the fluorination of organic spacer cations can impact on the perovskite crystal structure and photovoltaic performance …”

“…Previous literature reported that introducing fluorine atoms on the organic cation of perovskite might distort the crystal structure and subsequently modify the optoelectronic properties of perovskite . Thus, we examined the crystal structure of 2D RPPs using X‐ray diffraction (XRD) measurement.…”

Pseudohalide induced tunable electronic and excitonic properties in two-dimensional single-layer perovskite for photovoltaics and photoelectronic applications

“…The van der Waals interaction between organic cations and inorganic anions in 2D perovskite is so large that it takes more energy to destroy the 2D crystal structure, leading to excellent stability compared to the 3D perovskites [17][18][19] . Furthermore, the hydrophobic long alkyl chain or aromatic group can significantly improve their stability to moisture [20] . Tunable electronic properties, intriguing optical properties, and quantum well (QW) structures of 2D perovskites also open new avenues for a variety of applications [21][22][23][24] .…”