How Strong Is the Hydrogen Bond in Hybrid Perovskites?

Abstract

Hybrid organic–inorganic perovskites represent a special class of metal–organic framework where a molecular cation is encased in an anionic cage. The molecule–cage interaction influences phase stability, phase transformations, and the molecular dynamics. We examine the hydrogen bonding in four AmBX3 formate perovskites: [Am]Zn(HCOO)3, with Am+ = hydrazinium (NH2NH3+), guanidinium (C(NH2)3+), dimethylammonium (CH3)2NH2+, and azetidinium (CH2)3NH2+. We develop a scheme to quantify the strength of hydrogen bonding in these systems from first-principles, which separates the electrostatic interactions between the amine (Am+) and the BX3– cage. The hydrogen-bonding strengths of formate perovskites range from 0.36 to 1.40 eV/cation (8–32 kcalmol–1). Complementary solid-state nuclear magnetic resonance spectroscopy confirms that strong hydrogen bonding hinders cation mobility. Application of the procedure to hybrid lead halide perovskites (X = Cl, Br, I, Am+ = CH3NH3+, CH(NH2)2+) shows that these compounds have significantly weaker hydrogen-bonding energies of 0.09 to 0.27 eV/cation (2–6 kcalmol–1), correlating with lower order–disorder transition temperatures.

Controlling Homogenous Spherulitic Crystallization for High‐Efficiency Planar Perovskite Solar Cells Fabricated under Ambient High‐Humidity Conditions

“…This mechanism is likely because water has stronger bond affinity to DMF, DMSO, and NMP, respectively, than to itself, resulting in a complex formation . As perovskite structure is held together by weak hydrogen bonding, even weaker bonding is to be expected in the metastable adduct phase, which would make the Lewis bases highly labile to sequestering by water . Figure S2 of the Supporting Information illustrates the proposed mechanism, which is an extension of a previously proposed mechanism of intermolecular exchange of Lewis bases in adduct by organic cation …”

Synergy of Hydrophobic Surface Capping and Lattice Contraction for Stable and High‐Efficiency Inorganic CsPbI2Br Perovskite Solar Cells

“…In just a few years, the most celebrated perovskite solar cells have achieved power conversion‐efficiency (PCE) as high as 23.2% . However, their poor stability has been a challenging problem, mainly due to the inherent instability of their organic components . Gratifyingly, by replacing the organic cation with Cs + , their compositional stability is greatly improved …”

Stability and flexibility of heterometallic formate perovskites with the dimethylammonium cation: pressure-induced phase transitions

“…23 The HB energy is calculated following the procedure described elsewhere. 4,24 The total electrostatic interaction is calculated as the energy required to remove one cation from the unit cell, and the dominating monopole term is estimated as the energy required to remove a single atom cation (here Cs + ) from the same cage. Subtracting the monopole part of the electrostatic interaction from the total electrostatic interactions, the dipole and higher order terms remain, and these are assumed to be dominated by the HBs.…”

“…Subtracting the monopole part of the electrostatic interaction from the total electrostatic interactions, the dipole and higher order terms remain, and these are assumed to be dominated by the HBs. Note that we use the same computational setup here as in previous works 4,24 and the calculated HB energies should thus be directly comparable.…”

“…Structural optimisation is performed using DFT calculations. The optimised unit cell parameters of the DMANaCr and DMAKCr compounds are compared with the experimental values and with the values obtained for the previously calculated DMAZn framework 24 in Tab. S1.…”